BOUGHT WITH THE INCOME 
 FROM THE 
 
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 THE GIFT OP 
 
 Henvg W. Sage 
 
 1891 
 
 ..A.-./4335W 2^/2//?^, 
 
Cornell University Library 
 arV18413 
 
 Elementary human physiolog 
 
 3 1924 031 268 620 
 
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Cornell University 
 Library 
 
 The original of tliis book is in 
 the Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924031268620 
 
ELEMENTARY 
 
 HUMAN PHYSIOLOGY 
 
 JOHN GRAY M'KENDRICK, M.D., F.R.S., 
 
 PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF GLASGOW 
 
 WITH 164 WOODCUTS 
 
 W. & R. CHAMBERS, Limited 
 
 LONDON AND EDINBURGH 
 
 1896 
 
Ediuburgli : 
 Printed by W. & R. ChamberSj Limited. 
 
PREFACE. 
 
 Twenty years ago I wrote for Messrs W. & R. Chambers a small 
 Manual on Animal Physiology. The present work is based on that 
 book, but the chapters have been almost wholly rewritten, and they 
 have been rearranged to suit the Syllabus of the First or Elementary 
 Stage issued by the Department of Science and Art. The publishers 
 have been able to place at my disposal a larger number of illustrations 
 than are usually met with in an elementary work ; and I would point 
 out to both teachers and pupils that much valuable information may 
 be derived by a careful study of the descriptions of the woodcuts. To 
 aid in testing the advancing knowledge of the pupil, numerous ques- 
 tions have been introduced, usually at the close of a chapter, and 
 reference is made to the paragraph where an answer may be found. 
 
 The general scope of the work and a statement of my notions as to 
 how Elementary Human Physiology may be effectively taught in a 
 school, will be found in the following extracts (with emendations) 
 from the preface to the book on Animal Physiology. 
 
 It is now universally admitted that an acquaintance with the prin- 
 cipal phenomena manifested by living beings, and more especially 
 with the structure and mode of action of the different parts of the 
 human body, is one of the most important branches of knowledge 
 for men and women in all conditions of life. It is, therefore, no 
 longer necessary to advocate the study of Physiology as a part of 
 general education. 
 
 The object of the present text-book is to aid in this work. It pro- 
 fesses to give such an account of the general mechanism and functions 
 of the human body as ought to be known by every well-educated 
 person. While aiming at brevity and clearness, the author has not 
 attempted to avoid the use of technical terms, because such terms 
 frequently express in a word a meaning which can only be conveyed 
 in familiar language by circumlocution, and with the risk of vagueness. 
 Many of the best of these terms have been handed down to us for 
 generations, and they have become clear and definite symbols of 
 thought. To attempt to teach a science without them will simply 
 result in giving the pupil vague and superficial notions, so that if he 
 should be obliged again to study the subject with the view of entering 
 one of the professions for which it forms a special branch of training, 
 he will find that he has to learn the science anew. Many technical 
 
4 PREFACE. 
 
 terms, however, have been explained, and their derivation given, in 
 the Index. 
 
 To aid both in teaching and in learning, it will be observed that the 
 subject has been broken up into numerous divisions and subdivisions, 
 the headings of which have been so printed in diverse type as to catch 
 the eye, and thus impress the memory. 
 
 To teach physiology efficiently, it will be a great assistance to the 
 teacher to have the following appliances : 
 
 (1) A human skeleton, or the skeleton of any of the higher animals, 
 such as a monkey, a dog, a cat, or a rabbit. Any of these may be 
 obtained by applying to any well-known bookseller or surgical- 
 instrument maker. 
 
 (2) A good microscope, capable of magnifying about 300 diameters. 
 The one recommended by the author is No. IV. of Carl Reichert of 
 Vienna, with objectives Nos. 3 and 7, at a cost of about ;^3, los. By 
 means of this instrument, which ought to be provided by the author- 
 ities as part of the educational appliances of every school, a teacher 
 can demonstrate the simpler tissues and fluids found in the body, and 
 he will also be able to interest his pupils by showing infusoria, the 
 humbler forms of plant life, &c., many of which may be found in the 
 water of every stagnant pool by the roadside. ' 
 
 (3) A set of diagrams. These may be made by copying in Indian 
 ink on a large scale, on cartridge paper, the woodcuts in this work. 
 Photographs may also be easily taken of any of the illustrations, and 
 lantern slides prepared. An occasional lantern demonstration, after 
 the pupils have gone over the part of the subject to be illustrated, 
 will be of great value. 
 
 (4) Dissected preparations. These may readily be procured by 
 dissecting a rabbit. Skin the front part of the body, and also a limb ; 
 clear off the loose tissue covering the muscles of the limb ; separate 
 the muscles from each other ; expose the chief nerves and vessels in 
 the limb ; open the chest and abdomen, so as to be able to point out 
 the appearance and position of the chief organs ; and open the head, 
 so as to expose the brain. 
 
 By such objective methods, after a little practice, the work of the 
 teacher will become easy, and sound notions of anatomical structure 
 and of physiological action will be taught. 
 
 I have to thank my assistant, Dr David Eraser Harris, for reading 
 the proof-sheets. 
 
 JOHN G. M'KENDRICK. 
 
 Universitv of Glasgow, March 1896. 
 
CONTENTS. 
 
 PAGE 
 
 INTRODUCTORY 7 
 
 DIVISION I.— GENERAL PHYSIOLOGY. 
 
 Chapter I. — General View of the Anatomy of the Body — A. 
 The Parts of the Skeleton — Vertebral Column — Vertebrae 
 — Sacrum — Skull — Thorax — Upper Extremity — Lower 
 Extremity — Erect Posture — the Joints — B. The Soft Parts 
 of the Body — the Muscles — the Connective Tissues — the 
 Skin — Mucous Membranes — C. The Internal Organs — 
 the Central Nervous Organs — the Organs of Digestion 
 — the Organs of Respiration — the Genito-urinary Organs 
 — the Organs of the Circulation 1 1-5 1 
 
 Chapter II. — Chemical Constitution of the Body and the Chemi- 
 cal Changes occurring in it — Elementary Constituents — 
 Compounds — Inorganic Compounds — Organic Compounds 
 — Chemical Changes 52-64 
 
 Chapter III. — The Body in Action — Introductory — Heat — 
 Food — Waste of Matter — ^ Waste of Energy — Phenomena 
 in a Muscle — the Blood — Absorption of Waste Matters 
 — Removal of Waste Matters — Formation of Blood — 
 General Influence of Nervous System — Reflex Acts — the 
 Brain and Cord — Erect Posture — Life — Death 65-78 
 
 DIVISION IL— HISTOLOGY. 
 
 Chapter I. — The Structure and Functions of the Elementary 
 Tissues — Molecular Elements — Cellular Elements — Proto- 
 plasm — Epithelium and Endothelium — Pigment — Fat — 
 Fibrous Elements — White Fibrous Tissue — Yellow Elastic 
 Tissue — Muscular Tissue — Work done by a Muscle — 
 Tubular Elements — Cartilage — Bone — Growth of Bone.. 79-100 
 
 DIVISION III.— SPECIAL PHYSIOLOGY. 
 
 Chapter I. — The Blood — General — Microscopical Appearance 
 — Blood-corpuscles of various Animals — Chemical Con- 
 stitution of Plasma — Coagulation — Chemical Composition 
 of Corpuscles 101-104 
 
 Chapter II. — Circulation of the Blood — Structure of Blood- 
 vessels — the Heart — Course of Circulation — Elasticity of 
 Arteries — Contractility of Arteries — Veins — Influence of 
 Respiration — Pulse — Capillaries 105-1 1 7 
 
 Chapter III. — The Alimentary System — General — Food — Air — 
 Water — Classification of Foods — Quantity of Food — Food 
 and Work — Varieties of Foods — Mastication — Insalivation 
 — Deglutition — Stomach — Mucous Membrane of Stomach 
 — Changes in Stomach — Gastric Juice — Alexis St Martin 
 — Absorption — Time required for Digestion — Intestines — 
 
6 CONTENTS. 
 
 PAGE 
 
 Mucous Membrane of Intestines — Villi — Muscular Coat — 
 Bile — Chemistry of Bile — Pancreas — Pancreatic Juice — 
 Intestinal Juices — Micro - organisms in Bowel — Great 
 
 Intestine — Faeces 1 18-142 
 
 Chapter IV. — Absorption of Nutritious Matter — General — 
 
 Chyle 143-145 
 
 Chapter V. — Sanguification — General — Blood-glands — Lymph 
 — Blood, Chyle, and Lymph contrasted — Spleen — other 
 
 Blood-g&nds HS-iJi 
 
 Chapter VI. — The Liver — General Description — Circulation in 
 Liver — Functions of Liver — Bile — Fat — Glycogen — Urea 
 
 —Waste Haemoglobin— Fate of Biliary Matters 151-158 
 
 Chapter VII. — The Respiratory System — General — Conditions 
 of Respiration — Special Anatomy of Respiratory Organs — 
 Respiratory Process — Respiratory Movements — Capacity 
 of Lungs — Abnormal Breathing — Ventilation — Essential 
 
 Nature of Respiratory Process 1 59-1 70 
 
 Chapter VIII. — Nutrition and Secretion 170-172 
 
 Chapter IX. — The Kidneys — General Description — Special 
 Points in Structure — Urine — Mode of Action of Kidney — 
 Quantity of Urinary Constituents — Amount of Urine — 
 
 Bladder 173-176 
 
 Chapter X. — The Skin — General — Secretion of Sweat — Func- 
 tions 177-178 
 
 Chapter XL — Animal Heat 179-180 
 
 Chapter XII. — Animal Mechanics — Mechanical Arrangement of 
 Muscles — Levers of First Order — Levers of Second Order 
 — Levers of Third Order — Equilibrium — Locomotion... 1 80- 184 
 Chapter XIII. — The Senses — Introduction — Touch — General 
 — Nature of Touch — Sensations of Temperature — Taste — 
 General — Conditions of Taste — Smell — General — Physical 
 Causes of Smell — Conditions of Smell — Sight or Vision 
 — General — Anatomy of Eye — Mechanism of Vision — 
 Accommodation — Blind Spot— Defects of Vision — Sub- 
 jective Phenomena of Vision — Position of Objects on the 
 Retina — Sizes of Objects — Binocular Vision — Hearing — 
 Anatomy of Ear — Structure of Internal Ear — Structure 
 of Cochlea — Functions of Parts of Ear — Range of Hearing 
 
 — The Muscular Sense 1 84-2 1 1 
 
 Chapter XIV. — The Nervous System — General Description — 
 Nervous Matter — Nerves — Nerve-cells — Functions of a 
 Nerve-fibre — Development of Nervous System in Animal 
 Kingdom-— Nervous System of Invertebrates — Nervous 
 System of Vertebrates — the Human Brain — Functions of 
 different parts of Brain — Motor Areas — Functions of 
 Nerves — Cranial and Spinal Nerves — the Spinal Cord — 
 
 Sympathetic System 211-230 
 
 Chapter XV. — Voice and Speech 230-233 
 
 INDEX 234-240 
 
ELE M ENT ARY 
 
 HUMAN PHYSIOLOGY. 
 
 INTRODUCTORY. 
 
 When we examine the natural objects by which we are 
 surrounded, we have little difficulty, as a rule, in distinguish- 
 ing those which are dead from those which are living. 
 Living things have certain properties not possessed by dead 
 things. Thus, living things are produced, in the first 
 instance, by living things like themselves, and they increase 
 in size and grow by taking dead matter into themselves and 
 making it alive ; there are constant exchanges taking place 
 between them and the outer world — in other words, they 
 eat, and breathe, and excrete, taking in matter and giving 
 it out again ; they often move about apparently spon- 
 taneously ; they produce more or less heat by chemical 
 changes in their tissues; and, lastly, they usually pass 
 through a kind of cycle in their life history. They are 
 produced, they grow, they reach maturity, they decline, and 
 they die. All living things do not manifest these properties 
 to the same degree, and some of these properties may be 
 so hidden as not to be readily observed. Still it is true 
 that all living things — the lichen on the wall, the sea-weed, 
 the flowering plant, the tree on the one hand, and the sea 
 
8 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 anemone clinging to the rocks, the limpet, the fish, the 
 snake, the bird, the rabbit, the ox, and man, on the other — 
 show the same essential phenomena of life. The science 
 that studies and describes these phenomena is called 
 Physiology, an old term meaning a description of nature, 
 and once embracing all physical phenomena, but now 
 limited to those met with in living beings. The science 
 consists of two great divisions — Animal Physiology and 
 Vegetable Physiology. As the latter belongs to the pro- 
 vince of the botanist, we have nothing directly to do with 
 it in this work, which will be devoted to a short exposition 
 of the chief facts relating to the mechanism of the animal 
 body, and more especially to that of the body of man. 
 
 Anatomy. — We may examine the body when it is 
 dead by the art of dissection, as practised by the anatomist. 
 He opens the cavities, separates one part from another, 
 describes the position and relations of the various organs, 
 and thus obtains knowledge of the general build or frame- 
 work of the body. This constitutes the science of 
 Anatomy, and it is clear that, before we can hope to ex- 
 plain how the body works, we must know something of the 
 structure of its parts. An engineer could never thoroughly 
 understand the working of a steam-engine unless he had 
 seen an engine built up bit by bit, wheel and piston and 
 axle and bolts all mutually adjusted. 
 
 When the body of a man is looked at by the uninitiated, 
 it appears to be so complex in structure as almost to baffle 
 investigation ; but, in the course of ages, men have suc- 
 ceeded by dissection in obtaining a tolerably accurate 
 knowledge of the parts of which it is composed, so far as 
 these can be seen by the naked eye. In more recent 
 times, also, the microscope has been used for the examina- 
 tion of the minute structure of every organ and tissue ; so 
 that, while the department of microscopic anatomy is still 
 far from having been completely worked out, every year is 
 
INTRODUCTORY. 9 
 
 adding to our knowledge. In describing the general 
 anatomy of the body, therefore, it is convenient to divide 
 it into (a) what may be seen with the naked eye ; and (i) 
 what can only be recognised with the microscope. In 
 this Elementary Course the microscopical structure of the 
 tissues and organs will be discussed very briefly. 
 
 Chemistry. — We obtain information regarding the nature 
 of many things by submitting them to analysis, and resolv- 
 ing them into the chemical elements of which they are 
 composed.' Thus the chemist is able to tell us that a piece 
 of chalk consists of carbonate of lime, which in turn may 
 be decomposed into calcium, oxygen, and carbonic acid. 
 In like manner, we may submit matter that was once alive, 
 such as a bit of muscle or bone, to analysis, and ascertain 
 the chemical compounds and the elements that exist in it. 
 Such a proceeding, however, although it yields valuable 
 information, does not teach much as to the chemical 
 changes that occurred in matter when it was alive. Thus 
 an analysis of muscle or flesh does not throw light on 
 the chemical changes that occur in living muscle, nor does 
 an analysis of the tissue of the lung tell us much about 
 the changes in respiration. To understand the chemical 
 changes in living matter which are intimately associated 
 with the phenomena of life, we must analyse the substances 
 that enter living matter, and the substances that issue from 
 it, and then draw conclusions as to the changes that 
 probably occur. For example, the true nature of respira- 
 tion can be understood only by an analysis of the air before 
 it enters the lungs in inspiration and after it has issued from 
 the lungs in expiration, and by analysing the gases that 
 exist in the blood flowing through these organs. We thus 
 find that the essential change in breathing is that oxygen 
 gas passes from the air into the blood, and that carbonic 
 acid gas passes from the blood into the air. Thus, by 
 studying (a) the chemical composition of the body and (i) 
 
10 ELEMENTARY HUMAN tHYSIOLOGY. 
 
 the chemical changes that occur in it, we are able to draw 
 some conclusions as to the chemical phenomena or changes 
 that appear to lie at the basis of all vitality. 
 
 The Body in action. — Having studied the analytical 
 structure of the body, its chemical constitution, and the 
 chemical changes that occur in it, we next proceed to view 
 the body in "action. We find it is composed of certain 
 parts that are devoted to special uses. Such parts are 
 termed organs, and each organ performs one or more 
 FUNCTIONS. By the function of an organ, we mean the 
 part it has to play in the general mechanism. Thus the 
 heart is a kind of pump for driving the blood through the 
 vessels ; the lungs are organs concerned in respiration ; and 
 the kidneys have as their function the elimination of water 
 and other substances. Again, we find groups of organs 
 associated in systems or groups for special purposes, as the 
 bones and muscles in locomotion ; the heart, arteries, and 
 veins in the circulation ; and the stomach and intestines in 
 digestion and absorption. All the organs and systems of 
 organs are more or less under the control of the nervous 
 system, which includes the organs known as the brain, 
 spinal cord or marrow, the nerves, and the organs of 
 sense. 
 
 It will thus be seen that there is a general and also a 
 more special way of viewing the mechanism of the body. 
 We shall discuss first those matters of general importance 
 that relate to its anatomical structure, chemical constitu- 
 tion, and mode of action as a whole, and then we shall take 
 up the function of the organs and systems of organs more 
 in detail. The subject is thus divided into General and 
 Special Physiology. 
 
 Questions. 
 
 What do you understand to be the distinctions between the 
 
 sciences of Anatomy and Physiology ? 
 Define the terms ' organ,' ' function,' and ' system.' 
 
11 
 
 DIVISION I.— GENERAL PHYSIOLOGY. 
 
 CHAPTER I. 
 
 GENERAL VIEW OF THE ANATOMY OF THE BODY. 
 
 The body contains fluids and solids. The fluids are 
 very abundant, existing not only in certain vessels or tubes 
 fitted for their reception, but permeating the solid parts. 
 Without these fluids the solid parts of the body would die. 
 -The solid parts consist chiefly of hard resisting parts termed 
 the bones, of softer structures forming muscle or flesh, 
 and of the various organs of the body, such as the brain, 
 the lungs, or the heart. 
 
 The Locomotive Apparatus consists of two kinds of 
 organs — the bones and the muscles. The bones, which are 
 hard firm structures, form levers joined to each other 
 by firm or movable articulations or joints, which often 
 permit the bones to move on each other with great facility. 
 The muscles constitute the chief part of what is usually 
 called flesh, and they possess the property of contract- 
 ing or shortening so as to move the bones to which 
 their ends are attached. The bones may be called the 
 passive, and the muscles the active, organs of locomotion. 
 
 A. THE PARTS OF THE SKELETON. 
 
 1. The Skeleton as a whole. — The whole of the 
 bones in their natural position form the skeleton, which may 
 be divided into the trunk and the limbs. The entire 
 skeleton of an adult consists of two hundred bones, 
 namely : 
 
ELEMENTARY HUMAN PHYSIOLOGY. 
 
 CERVICAL VERTEBRA- 
 
 DORSAL 
 ERTEBR>G 
 
 Fig. 1. — Human SJceleton viewed in front. 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. I3 
 
 1. The spine or vertebral column, including the sacrum 
 
 and coccyx 26 
 
 2. The cranium 8 
 
 3. The face 14 
 
 4. The hyoid bone, sternum, and ribs 26 
 
 5. The upper extremities 64 
 
 6. The lower extremities 62 
 
 The trunk consists of, first, the 
 spine or vertebral column (figs. 1, 
 2), a flexible stalk formed of a 
 number of distinct bones articu- 
 lated one below the other ; 
 second, the head, containing the 
 brain and organs of sense, and 
 consisting also of numerous 
 bones ; and third, the thorax or 
 chest, composed of detached 
 arches called the ribs, and which 
 are connected in front, by carti- 
 lage or gristle, with a single bone, 
 the sternum. The thorax con- 
 tains the principal organs of 
 respiration and circulation. 
 
 The limbs, four in number, are 
 termed superior and inferior. In 
 man, the inferior limbs support 
 the trunk, while the superior bear 
 the hands, which serve as organs 
 of prehension ; but in the lower 
 mammalia, as in the horse or dog, 
 all four support the trunk. The 
 superior limbs are divided into 
 the shoulder, the arm, the fore- 
 arm, and the hand. The inferior 
 limbs comprise the haunch or 
 pelvis, the thigh, the leg, and 
 
 200 
 
 DR 
 
 Fig. 2. — Axis of Spine, A, A : 
 
 C, cervical (neck) vertebrae^ 
 
 D, dorsal (back) vertebrae ; 
 
 L, lumbar (loin) vertebrae : 
 
 S, sacrum ; Coc, coccyx. 
 
14 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 the foot. In birds, the anterior or superior limbs con- 
 stitute wings. 
 
 2. The Vertebral Column. — This consists of twenty- 
 four free bones called vertebrae, and of two bones at the 
 lower extremity, each composed of several vertebrae, termed 
 the sacrum and coccyx. Superiorly, it supports the skull ; 
 laterally, it has attached to it the ribs, through which 
 it supports the weight of the upper limbs; and at its 
 lower extremity it rests on the bones of the pelvis, which 
 
 Fig. 3. — Dorsal Vertebra 
 viewed from above : 
 
 I, body : 2, pedicels ; 3, lam- 
 inae ; 4, ring ; 5, spinous 
 process ; 6, transverse pro- 
 cess : 7, articular process for 
 next vertebra ; f, facet for 
 head of rib ; d, facet for 
 tubercle of rib. 
 
 Fig. 4. 
 
 Section of Intervertebral Disc : 
 
 f£, f2, vertebrae ; h^ disc ; r, spinous process. 
 
 transmit the weight of the body to the lower limbs. It 
 also affords support and protection to the spinal marrow 
 by enclosing it in a canal of bone. The bones of which it 
 is composed are bound together by ligaments or bands, and 
 by elastic discs of a fibrous and gristly substance called 
 the intervertebral discs (fig. 4, b). There is thus secured 
 great strength combined with flexibility. A certain amount 
 of movement occurs between individual vertebrae, more 
 especially in the cervical region. 
 
 3. General Characters of a Vertebra. — Each verte- 
 bra has more or less the form of a ring, and presents 
 a body (fig. 3, i), which is placed anteriorly ; a ring, 4 — 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 1 5 
 
 containing the spinal cord and its membranes — which is 
 formed by the body, i ; the pedicels, 2 ; the laminse, 3 ; 
 and the spinous process, 5. Attached to the ring we 
 find the transverse processes, 6, placed one on each side, 
 and the articular processes, also one on each side, 7, two 
 superior and two inferior, for connection with the adjoining 
 vertebrae. 
 
 4. Characters peculiar to groups of Vertebrae. 
 — The vertebrae are divided into three groups — cervical, in 
 
 Fig. 5. — First Vertebra or Atlas: Fig.6. — Second Vertebra or Axis: 
 
 A, ring for spinal cord ; B, ring for r, odontoid process; 2, articulation for 
 
 odontoid process of axis ; dotted line atlas ; 3, canal for vertebral artery ; 
 
 indicates ligament ; i, articulation 4, spinous process ; 5, articulation for 
 
 for occipital bone ; 2, transverse pro- third cervical vertebra, 
 cess : rt, canal for vertebral artery. 
 
 the neck ; dorsal, in the back ; and lumbar, in the loins. 
 Of the first there are seven ; of the second, twelve ; and of 
 the third, five (fig. 2). The first cervical, which supports 
 the head, is called the atlas (fig. 5), and the second, the 
 axis. The atlas has no body, and development shows that 
 
 Fig. 7. — Cervical Vertebra : 
 I, body : J, ring ; 3, bifid spinous pro- 
 cess ; 4, transverse process ; 5, canal 
 for vertebral artery. 
 
 Fig. 8. — Lumbar Vertebra : 
 
 i, body ; 2, transverse process ; 3, spinous 
 
 process ; 4, articulation for next ver- 
 
 for vertebral artery. tebra. 
 
 the process called the odontoid process of the axis (fig. 6, i) 
 
i6 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 is in reality the body of the atlas connected with the body 
 of the axis. The atlas, bearing the head, rotates round 
 this process when the head is moved 
 from side to side. The general 
 characters of a cervical vertebra are 
 seen in fig. 7, the two chief points 
 being the notched spinous process, 
 3, and the canal in the transverse 
 process for the vertebral artery, 5. 
 The chief character by which a 
 dorsal vertebra may be recognised 
 on the body or 
 
 Fig. 9. — Front of Sacrum: Jg the 
 I , upper end : 2, lower end for 
 
 presence 
 transverse process of an articulatina; 
 
 coccyx : vi — V5, vertebrae * ^ 
 
 united ; a, foramina or surfacc for the head Or angle of the 
 
 holes for sacral nerves; 3, ^b (seC fig. 3, C, d). The lumbar 
 articulation of pelvic bone. ^ *^ n\ ^ , . , ,. 
 
 vertebrae (fig. 8) have their bodies 
 more massive than those of the dorsal, and the spinous 
 
 D Fig. 10. —Side View 
 
 of Human Skull : 
 
 a, frontal bone ; 5, pari- 
 etal bone : c, occipital 
 bone ; d, temporal 
 bone (squamous por- 
 tion) ; £, sphenoid 
 bone ; ^ malar bone ; 
 ffj nasal bone ; /i, 
 superior maxillary or 
 upper jaw-bone ; /, 
 inferior maxillary or 
 lower jaw-bone. 
 
 BD, height of cranium ; 
 GO, length of crani- 
 um ; BN, basi-nasal 
 length ; BA, basi-al- 
 veolar length. (These 
 measurements are 
 supposed to be made 
 in a straight line from 
 point to point.} 
 
 processes are large, flat, and point directly backwards 
 instead of downwards (fig. 2, L). 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 1 7 
 
 5. The Sacrum (figs. 1, 2, and 9) is placed below the 
 last lumbar vertebra, above the coccyx, and between 
 the pelvic bones (fig. 1). It consists in early life of five 
 vertebrae, which in the adult are united into one bone. 
 The coccyx, at the lower extremity of the vertebral column, 
 consists of four rudimentary vertebrae, which diminish in 
 size from above downwards (figs. 2 and 18). 
 
 The average length of the vertebral column is about 
 28 inches, and it presents four curves in its course, the 
 convexity being forwards in the neck and loins, and back- 
 wards in the back and pelvis (fig. 2). 
 
 6. The Skull is sup- 
 ported on the vertebral 
 column, and is formed of 
 a number of bones, all of 
 which, with the exception 
 of the lower jaw, are firmly 
 fixed together by surfaces 
 termed sutures. It is di- 
 vided into two portions — 
 tlie cranium and the face. 
 The cranium protects the 
 brain; the face surrounds 
 the nose and mouth, and 
 contains several of the 
 organs of sense. The 
 cranium (fig. 10) is com- 
 posed of eight bones — 
 namely, the occipital, c; 
 the two parietal, b; the 
 frontal, a; the two tem- 
 poral, d; the sphenoid, e ; 
 and the ethmoid. The 
 sphenoid forms part of the 
 base of the skull (a little in front of 5, fig. 11), and the 
 
 Fig. U.— Base of Skull : 
 
 i, superior maxillaries ; 2, 2, palate ; 3, 
 vomer ; 4, wing of sphenoid ; s, basilar 
 process of occipital ; 6, foramen magnum ; 
 7, foramen ovale ; S, temporal ; 9, 11, 
 styloid process of temporal; 12, mastoid 
 process. 
 
i8 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 ethmoid is found (immediately above and behind N in fig. 
 10) between the orbital plates of the frontal bone, and 
 enters into the formation of the orbits and the nasal cavities. 
 The /ace is composed of fourteen bones, of which twelve are' 
 in pairs, the two superior maxillary (fig. 10, A, and fig. 
 11, ., i), the malar (fig. 10,/), the nasal (fig. 10, g), the 
 
 9.8.,'^, 
 
 Fig. 12.— The Ribs, in situ : 
 I and 2 are the upper and the middle parts of the 
 sternum or breast-bone ; 3, its ensiform cartilage ; 
 4, the first dorsal, and 5 the ]a£t (or twelfth) 
 dorsal vertebra ; 6, the first rib ; 7, its head ; 8, 
 its neck, resting against the transverse process 
 of the first dorsal vertebra ; g, its tubercle ; 10, 
 the seventh or last true rib; 11, the costal car- 
 tilages of the true ribs ; 12, the last two false 
 ribs or floating ribs. 
 
 palate (fig. 11, .<, 2), 
 the lachrymal (a little 
 to the right of ^ in the 
 orbit, fig. 10), and the 
 inferior turbinated in 
 the nose ; and two 
 single, namely, the 
 vomer, a bone forming 
 a partition between 
 the two nostrils (fig. 
 II, 3), and the inferior 
 maxillary (fig. 10, i). 
 
 7. The Cranial 
 Cavity is seen on 
 sawing off the roof of 
 the skull. The walls 
 consist of two layers 
 of compact tissue, the 
 duier and inner tables, 
 and between these 
 a cellular structure 
 
 known as the diploe. 
 The tipper part of 
 the cranial cavity 
 forms an arch, and the lower is divided into three parts 
 having different levels, called the anterior, the middle, and 
 the posterior fossae, in which the anterior and middle lobes 
 of the cerebrum and the cerebellum rest. The base is per- 
 forated by numerous openings for the passage of nerves 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 
 
 19 
 
 and blood-vessels. The most notable of these openings 
 is the foramen magnum (fig. 1 1, e), for the passage of the 
 spinal marrow and of certain blood-vessels. 
 
 8. The Thorax, or chest, consists of the dorsal verte- 
 brae, the sternum or breast-bone (fig. 12), the ribs, and the 
 cartilages connecting these with the sternum, known as 
 the costal cartilages. The sternum, 1-3, is situated in the 
 median line at the fore-part of the thorax, and is con- 
 nected with the rest 
 of the trunk by the 
 costal cartilages of 
 the seven highest 
 pairs of ribs, n, n. 
 The ribs are twelve 
 in number on each 
 side. They are long 
 slender curved bones 
 which extend for- 
 wards from the spine, 
 some of them join- 
 ing the breast-bone 
 or sternum. The 
 seven upper ribs, 
 which join the ster- 
 num by cartilages, 
 are termed the ' true ' 
 ribs ; while the lower 
 five, which do not 
 join the sternum, are termed the ' false ' ribs (see fig. 
 12, 12). Each rib has a double attachment to the back- 
 bone posteriorly; byits head, which unites with the body 
 of the vertebrae (fig. 3, c), and by a rounded prominence, 
 called the tubercle, with the transverse process of the 
 vertebra (fig. 3, ct). The ligaments binding the ribs to the 
 vertebral bones are seen in fig. 13. The costal cartilages 
 
 Fig. 13. — A Front View of the Articulations 
 of the Ribs with the Spinal Column ; 
 
 I, i, dorsal vertebrae ; 2, i, intervertebral cartilages : 
 3, 3, anterior common ligament; 4, neck, and 5, 
 head of rib ; 6, 7, 8, flat bundles of ligamentous 
 fibres (removed in the lowest rib shown in the 
 figure) ; 9, articulation between the tubercle of 
 the ribs and the transverse vertebral process. 
 
20 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 are continuations of the ribs. They give elasticity to the 
 framework of the thorax. In advanced life they become im- 
 pregnated with earthy matter, partially lose their elasticity, 
 and thus diminish the force and depth of respiration. 
 
 9. The Bones of the Upper Extremity. — The upper 
 extremity consists of the shoulder, the arm, the fore-arm, 
 
 and the hand. The bones of 
 the shoulder are the scapula 
 (fig. 1) or shoulder-blade, 
 and clavicle or collar-bone 
 (fig. 1) ; in the arm, is the 
 humerus (fig. 1) ; in the fore- 
 arm, are the radius and ulna ; 
 and in the hand, three groups 
 of bones — the carpus, meta- 
 carpus, and digital phalanges. 
 The scapula (fig. 14), placed 
 on the upper and back part 
 of the thorax, is attached 
 directly to the trunk only by 
 the clavicle, and from it the 
 
 ^. , , „ . ,r. r ^^ humcrus is suspended. The 
 Fiff. 14. — Posterior View of the , . , .' , ,. , . , 
 
 Left Scapula: '^'''"''' '« ^ l°"g cylindrical 
 
 The parts designated by the figures i, =, bonC placed On Cach sidc of 
 
 4, 6, 8, IP, II, 12, are sufficiently de- the neck, and Connecting the 
 
 scribed in the text; 3 is the superior . , -_ -, *\ . 
 
 border; 5. the external or axillary StCrnum With 12 (fig. 14), the 
 
 border ; 7, the inferior angle ; 9, the acromion prOCeSS of the 
 internal or vertebral border ; 12, the \ /c 1 r- \ mi 
 
 acromion process; 13, one of the SCapula (fig. 15, c). The 
 
 holes for the passage of an artery into humerUS (fig. 15, K) is an 
 
 the bone ; 14, the coracoid process. ■ _ r 1.1 1 • j • i i 
 
 imperfectly cylindrical bone, 
 extending from the shoulder to the elbow-joint In the 
 figure it is seen as it is placed when the arm is hanging 
 down and the palm turned forwards. It consists of a 
 head which articulates with the scapula at 6 (fig. 14), of 
 a shaft, and of a lower end, which supports the radius 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 21 
 
 and ulna. The two bones of the fore-arm are seen in fig. 
 15. They consist of the radius, r, which is the external 
 of the two bones of the fore-arm, and the tdna, u, which 
 is the internal. The radius articu- 
 lates above with the humerus, and 
 below with two of the bones of the 
 carpus, or wrist. The ulna articu- 
 lates with the humerus and the 
 radius, but is not directly connected 
 with the carpal bones, a thin, fibro- 
 cartilaginous disc being interposed 
 between its lower end and the 
 
 Fig. 15. — Bones of the 
 Human Arm : 
 h, humerus ; r, radius ; tt, ulna ; 
 w, wrist-joint; hd^ hand: f, 
 scapula ; c^ clavicle or collar- 
 bone. 
 
 Fig. 16.- 
 
 -Posterior Aspect of 
 , Left Hand. 
 For description, see text. 
 
 cuneiform bone (fig. 16, c). Wlien the arm and hand 
 hang downwards, the palm being directed forwards, the 
 position is called supination ; but when in the same posi- 
 tion the back of the hand is directed forwards, the posi- 
 tion is called pronation. These movements are effected 
 by the rotation of the radius on the lower end of the 
 humerus. The. carpus, or wrist, consists of eight short 
 
22 
 
 feLfiMENTARY HUMAU fHYSIOLOCV. 
 
 bones, arranged in two rows. Enumerated from the 
 radial or thumb side, they are (fig. 16), in the first row, 
 the scaphoid, sc; the semilunar, /; the cuneiform, c; and 
 pisiform, / ; and in the second row, in the same order, the 
 trapezium, / ; the trapezoid, t^ ; the os magnum, m ; and 
 the unciform, u. The metacarpus, forming the palm, con- 
 sists of five shafted bones which support the fingers, Wj, 
 ^2, OTg, m^, and m^. The digital phalanges are fourteen 
 in number, three for each finger, except the thumb, which 
 
 Fig. 18.— Pelvis : 
 
 I, lower lumbar vertebrae ; 2, 3, 4, sac- 
 rum : 6, 6, innominate bones ; 5, coc- 
 cyx : g, acetabula ; f^ symphysis 
 pubis ; I i Ijk k, brim of pelvis. 
 
 Fig. 17. — Outer Aspect 
 of Right Os Innomin- 
 atum or Iliac Bone : 
 
 A, ilium ; B, ischiiim ; C, pubis ; i, 
 crest of ilium; 2, anterior superior 
 spine ; 3, anterior inferior spine ; 4, 
 posterior superior spine ; 5, posterior 
 inferior spine ; 6, acetabulum ; 7, sym- 
 physis pubis : 8, descending ramus of 
 pubis ; 9, obturator foramen ; 10, as- 
 cending ramus of ischium ; 11, tuber- 
 osity of ischium. 
 
 has only two. In each instance, the proximal phalanx, /j, 
 is longer than the second, p^, and the second longer than 
 the third, p^. 
 
 10. The Bones of the Lower Extremity. — The 
 lower limb is divided into the haunch or hip, the thigh, 
 the leg, and the foot The haunch-bone on each side, 
 with the sacrum wedged in between, and bearing the coccyx 
 
General vie* of the anatomy of the body. 23 
 
 at its lower extremity, forms the peivis, which transmits the 
 weight of the body to the lower limb. It is usually called 
 the imiominate bone, or os coxm (fig. 17). The pelvis, at 
 basin (fig. 18), contains the urinary and generative organs 
 and the lower end of the alimentary canal. Its upper open- 
 ing is termed the inlet, and its lower the outlet pf the pelvis. 
 In the erect position (fig. 1), the pelvis is so inclined that 
 the plane of the brim forms an angle of from 60° to 65° 
 with the horizontal. 
 The line of pressure 
 of the weight of the 
 body on the sacrum 
 is downwards and 
 forwards towards 
 the junction of the 
 two innominate 
 bones termed the 
 symphysis pubis 
 (fig. 18,/), and the Fig. 19.— Front View Fig. 20.— Front View 
 pressure is com- of the Right Femur : of Right A, Tibia, 
 
 municated to the 
 heads of the thigh- 
 bones, which are 
 lodged in deep 
 depressions termed 
 the acetabula (fig. 
 17, e; fig. 18, 9; and fig. 1). The form and size of the 
 pelvis differ in the two sexes, as it is broader, more 
 expanded, and shallower in the female than in the male. 
 
 The femur, or thigh-bone (fig. 19), the largest bone of 
 the skeleton, articulates, 2, above with the acetabulum of 
 the OS innominatum (figs. 17, a, and 18, 9). In the erect 
 position it inclines inwards and slightly backwards, and 
 it is divisible into a shaft, having at one end a head, 2, 
 attached to it by a neck, 3, and bearing two rough promi- 
 
 :, shaft ; 2, head; 3, neck; 
 4, greater, and 5, lesser 
 trochanters ; 6, external, 
 
 1 and 7, internal tuber- 
 osity : 8, articulation for 
 tibia and patella. 
 
 and B, Fibula : 
 A — I, shaft ; z, articulation 
 with femur ; 3, articula- 
 tion with astragalus. B 
 — 4, shaft : 5, head ; 6, 
 lower end. Observe fork- 
 shaped cavity at lower 
 end for astragalus. 
 
24 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 nences for the attachment of muscles, called respectively 
 the great, 4, and the small, 5, trochanters ; and at the other, 
 or inferior extremity, a broad, irregularly shaped surface 
 called the external, 6, and internal, 7, condyles, for articula- 
 tion with the tibia. 
 In the female, from 
 the greater breadth of 
 the pelvis, the thigh- 
 bones converge more 
 towards their lower 
 extremity than in the 
 male. 
 
 'Y\\&patella or knee- 
 pan (fig. 1) is situated 
 in front of the knee- 
 joint, ^nd may be 
 regarded as a mass of 
 bone developed in the 
 tendon or sinew be- 
 longing to the great 
 muscle in front of the 
 thigh by which the 
 leg is extended on the 
 thigh. 
 
 The bones of the 
 leg are two in number, 
 the inner termed the 
 tibia or shin-bone (fig. 
 1, and fig. 20, A), 
 and the outer, the 
 The tibia alone com- 
 
 Fig. 21. — Upper View of Left Foot : 
 :, the astragalus, its upper articular surface ; 2, its 
 anterior extremity^ which articulates with 4, the 
 scaphoid bone ; 3, the os calcis, or heel-bone ; 
 4, the scaphoid bone ; 5, the internal cuneiform 
 bone ; 6, the middle cuneiform bone ; 7, the 
 external cuneiform bone ; 8, the cuboid bone ; 
 g, the metatarsal bones of the first and second 
 toes ; 10, II, the first and second phalanges of 
 the great toe ; 12, 13, 14, the first, second, and 
 third phalanges of the second toe. 
 
 fibula, or clasp-bone (fig. 20, B), 
 municates the weight of the trunk to the foot. It articu- 
 lates inferiorly with one of the bones of the ankle termed 
 the astragalus (fig. 21, i). The fibula is much more slender 
 than the tibia. 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 25 
 
 The foot is divided into the tarsus, the metatarsus, and 
 \he phalajtges. The tarsus consists of seven bones — namely 
 (fig. 21), the OS calcis, or heel-bone, 3; the astragalus, 
 which receives the weight of the body from the leg, i ; the 
 cuboid, so named from its shape, on the outer side of the 
 foot, 8 ; the scaphoid or navicular bone, 4, and the three 
 cuneiform or wedge-shaped bones intervening between the 
 scaphoid and the metatarsals, s, 6, 7 ; the metatarsal bones, 
 9, are five in number, and they bear the phalanges of the 
 toes, 10, II, 12, 13, 14. 
 
 The foot as a whole is admirably adapted for receiving 
 the weight of the body, and for affording stability. It is 
 arched from behind forwards, the posterior support of the 
 arch being formed by the heel, and the anterior by the 
 
 Fig. 22. 
 
 Section through the lower end of the tibia a, and through- the astragalus b, the 
 heel-bone c, the scaphoid bone </, the internal cuneiform bone e, and the bones of 
 the great toe^ 
 
 balls of the toes — indeed, the arch may be regarded as 
 having a single pier behind and a double in front (fig. 22). 
 II. Adaptation of the Skeleton of Man to the 
 ERECT POSITION. — The skull of man is nearly balanced on 
 the vertebral column (fig. 2), whereas in the lower animals 
 it is suspended, as it were, from the extremity of the column, 
 and is sustained by an elastic ligament (ligatnentum iiuchc£), 
 which runs from the spinous processes of the vertebrae to a 
 protuberance on the occipital bone. The body is balanced 
 
26 ELEMENTARY HUMAN fHYSlOLOGV. 
 
 on one or both of the lower limbs, which can be extended 
 in a straight line at the knee-joint. The foot of man alone 
 possesses an arched instep, and the great toe is not intended 
 for grasping, as in the monkeys, but for supporting weight 
 and giving elasticity to the step. The great length of the 
 femur enables the body to be balanced as in crouching, and 
 the great breadth of the pelvis enables the equilibrium to 
 be maintained even during considerable lateral movements. 
 The spinal column, by becoming broader inferiorly, is fitted 
 to sustain weight, and by means of its curvatures elasticity 
 and strength are secured, while a wide range of movement 
 is permitted. In man, the articular facet on the scapula 
 for the head of the humerus looks outwards, so as to allow 
 a free play of the upper extremity at the shoulder-joint. 
 Mobility, lightness, and delicacy of movement are permitted 
 by the structure of the upper limb, as contrasted with 
 strength and firmness in the lower, as may be seen on 
 comparing the shoulder, elbow, and wrist, with the hip, 
 knee, and ankle. 
 
 THE JOINTS. 
 
 12. General Description.— A joint is the union of any 
 two segments of the skeleton through the intervention of a 
 structure or structures of a different nature. Bone forms the 
 fundamental part of all joints ; strong bands or ligaments hold 
 the bones firmly together ; and in joints in which there is free 
 movement, we find the ends of the bones covered by cartilage or 
 gristle, and the joint lined by a smooth membrane termed a 
 synovial membrane. This membrane secretes a thin, watery 
 fluid, synovia, which lubricates the surfaces and diminishes 
 friction. Joints are divided into three classes : (i) those in 
 which the parts are continuous and there is no synovial mem- 
 brane between the bones, as seen in the construction of -the 
 skull (fig. 10) ; (2) those in which there is an intervening sub- 
 stance between the bones in the form of a disc or cushion 
 of fibro-cartilaginous substance, allowing a certain degree 
 of mobility, as in the articulations between the bodies of 
 
GENERAL VIEW Ot tHE Af^ATOMV OF THE 60DV. 2'J 
 
 the vertebrae (fig. 4) ; and (3) those in which we find a com- 
 plete joint having the ends of the bone covered with car- 
 tilage, the surface of which is lubricated by the synovial 
 fluid secreted from the delicate synovial membrane which 
 lines the fibrous coverings and all parts of the articulating 
 cavity except the cartilage (figs. 15, 22, and 23). In mov- 
 able joints the degree and nature of the movement are very 
 various, but four varieties may be noted : (i) Shifj^ng joints, 
 where there is merely a gliding motion between the ends of the 
 bones, as seen in the articulations between the bones of the 
 carpus or tarsus. In these cases the surfaces are plane, or one 
 is slightly concave while the other is slightly convex ; and the 
 motion is limited in extent and direction by the ligaments of 
 the joint, or by some projecting point of one of the bones. 
 (2) Ball and socket Joints, ■wh&iQ one hone presents a cup-like 
 depression, while the termination of the other assumes a hemi- 
 spherical or more or less globular shape, as in the hip-joint. 
 In such a joint, the ball is kept in apposition with the socket 
 by means of what is termed a capsular ligament (fig. 23, 14. 14), 
 which is an expansion of ligamentous structure, attached by its 
 extremities around the margins 
 of the articular surfaces com- 
 posing the joint, and forming 
 a complete investment of it, 
 but not so tight as to restrict 
 its movements too much. Fig. 
 23 shews the hip-joint, where 
 in addition we find a strong 
 round fibrous cord termed the 
 round ligament, 12, passing 
 from a depression in the head 
 of the femur to the -margin of 
 
 the acetabulum or articular ^ . , , , , ^ ,,. . . 
 
 ^, ... Section through the Lelt Hip-ioint. 
 
 cavity on the os tnnomtnat- ° ^ ' 
 
 , , ■ - i iL Eor description see text. 
 
 um, II. In such- a joint the 
 
 pressure of the air on the external surface assists in maintaining 
 apposition, for when a hole is bored through the floor of the 
 acetabulum so as to admit air into its cavity, the head of the 
 thigh-bone at once falls away as far as the ligaments will allow 
 
 Fig. 23. 
 
28 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 it. (3) Hinge joints, in which the contiguous surfaces are 
 marked by elevations and depressions, which exactly fit into 
 each other, so as to restrict motion to one direction. The 
 elbow and ankle joints are the best examples of this variety. 
 The knee-joint is not a pure hinge joint, because it admits of 
 a certain amount of rotation when the leg is slightly bent at 
 the knee. (4) Rotatory joints, which admit only of rotatory 
 motion. A pivot and ring are the essential parts of this joint, 
 the ring being generally composed partly of bone and partly of 
 ligament. The best example of this articulation is that between 
 the atlas (fig. 5, B) and the odontoid or tooth-like process of 
 the axis (fig. 6, i). 
 
 Questions. 
 
 I. Enumerate the bones found in the skeleton. 
 3, 4. Describe a vertebra, and point out the peculiarities which 
 distinguish a cervical from a dorsal vertebra. 
 
 6. Enumerate the bones entering info the formation of the skull. 
 
 7. What is the structure of one of the flat bones of the skull ? 
 
 8. Describe how the ribs are attached to the back-bone and to the 
 
 breast-bone. 
 
 9. Describe the bones entering into the formation of the elbow-joint 
 
 Enumerate the bones of the carpus. 
 
 10. Describe the general structure of the pelvis. What bones form 
 
 the ankle-joint ? 
 
 11. Show how the skeleton of man is adapted to the erect position. 
 
 12. Enumerate the different kinds of joints. Describe the hip-joint, 
 
 as regards bones, ligaments, and movements. 
 
 B. THE SOFT PARTS OF THE BODY. 
 
 a. THE MUSCLES. 
 
 13. Clothing the framework formed by the bones of the 
 skeleton, we find what is usually described as the flesh. 
 When this is carefully dissected, it is found to consist 
 mainly of certain organs termed the muscles. If we remove 
 the skin from one of the extremities, say the arm, we find 
 underneath it a strong fibrous covering termed the fascia, 
 which sends sheaths between the muscles, so that each 
 muscle is completely surrounded by it. The fascia is 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 29 
 
 usually divided into superficial and deep, the first being a 
 layer of loose tissue placed imniiediately below the skin 
 all over the body, and the latter is 
 that stronger layer of fibrous tissue 
 which lies close to the muscles, and 
 invests them in the manner already 
 indicated. On carefully removing 
 the fascia, the muscles may be dis- 
 played, as seen in fig. 24, which 
 represents the muscles of the human 
 arm. If we examine a single muscle, 
 as the biceps, o, it is found to be con- 
 nected with the bones at its two 
 extremities, and to present a fleshy 
 mass between the two attachments, 
 which are more tendinous or sinewy 
 in character. Each muscle may be 
 regarded as an organ having a special 
 function to perform. When irritated 
 during life, it possesses the property 
 of contracting or shortening itself, 
 and consequently of bringing its two 
 attachments nearer to each other. 
 
 If there be a joint between the two „. _ , „, , ,,, 
 
 Z ..... Fig. 24. — Muscles of the 
 
 attachments, the bones of this jomt Human Arm : 
 
 are moved upon each other in a aic, deltoid muscle ; rf, cor- 
 
 definite direction, and thus locomo- aco-brachiaiis musck ; n >■, 
 
 . triceps; e, i, extensors of 
 
 tlOn IS etieCteu (ng. <aO;. wrist and long supinator of 
 
 the hand ; k, m, flexor of 
 14. The various muscles found in the fingers and radial and ulnar 
 
 body may be conveniently classified sides of the wrist, and /, 
 
 ,. ,. , .. ,. palm of the hand, or pal- 
 
 accordmg to their mechanical action as ^^^^ ,„„g„,. ^_ p^,^^,;, 
 
 follows : Flexors, or those which bend brevis ; q, palmar fascia ; 
 
 the limbs, such as the biceps (fig. 24, ". Weeps. 
 
 o) ; extensors, which straighten the limbs, such as the 
 
 triceps, the fleshy mass on the back of the upper arm, r, r; 
 
3° 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 adductors, and abductors, which produce angular movement 
 to and from the median plane of the body such as the muscles 
 
 Fig. 25. 
 
 Shows a weight supported 
 on the palm of the hand, 
 ^ and raised iii the direc- 
 tion of the arrow by the 
 contraction of the biceps 
 muscle, d. Observe the 
 attachment of lower end 
 of iiicesps at e, and the 
 position of the elbow 
 joint 
 
 which enable us to move the thigh outwards and inwards 
 from the hip ; and rotators, which effect movement of a bone 
 round its axis without any great change of situation. As an 
 ' example of rotation, take those of pronation and supination 
 already referred to (p. 21). In pronation {pronus, with the 
 
 Fig. 26. 
 
 The Upper Limb, with the forearm and hand 
 in the state of supination : A, pronator muscle. 
 2) The same in a state of pronation : 6, the 
 supinator muscle. In both figures, a plumb-line 
 from the outer condyle of the humerus is found 
 to traverse the lower end of the ulna and the 
 ring-finger. - 
 
 face downwards), we turn the palm of the hand downwards as 
 in picking anything from the table ; in supination {supinus, 
 with the face upwards), we' turn the palm upwards, as for the 
 purpose of receiving anything that may be placed in it These 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY, 3 1 
 
 Fig. 27. — Muscles of Human Body. Deep muscles shown on left side : 
 a, flexors of hand and fingers; h, extensors of hand and fingers-; c, biceps; rf, 
 
 triceps ; f, deltoid ; /, pector^lis major ; g, serratus magnus ; h, gluteus ; /, t^ectus ; 
 
 k, extensorsofleg; /, sartorius; /«, gastrocnemius; «,tendo Achilles ; 1?, o, ligament* 
 
32 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 movements are effected by certain muscles causing the radius, 
 which bears the hand, to rotate round a longitudinal axis (see 
 fig. 26). One of the three muscles (A) passes from a projecting 
 process on the inner side of the humerus, at its lower end, to 
 the outer edge of the middle of the radius. When it con- 
 tracts, the radius rotates and rolls over in front of the ulna (as 
 in 2), and it is called a pronator muscle. A second muscle 
 (B) passes from a projecting process on the outer side of the 
 humerus to the inner side of the radius near its upper part. 
 It runs therefore in an opposite direction to the former muscle, 
 and produces an opposite effect, rolling the radius and hand 
 back into the position of supination. Hence it is called a 
 supinator. The third muscle, the biceps (fig. 24, 0), not only 
 bends the elbow, but from the mode in which its tendon is in- 
 serted, it also rotates the radius so as to supinate the hand, as 
 when we turn a screw or draw a cork. Supination can only be 
 performed to its full extent by man ; monkeys can partially effect 
 the movement, and in most of the lower animals the part corre- 
 sponding anatomically to the hand is constantly in a state of 
 pronation. Sometimes the combined action of various groups 
 of muscles may take place, as when we swing the arm round 
 and round in the shoulder-joint. This is termed circumduction, 
 when the limb is made to describe a cone by rotation round an 
 imaginary axis, the apex of the cone being in the joint. 
 
 A general view of many of the muscles of the human body 
 is given in fig. 27. 
 
 b. THE CONNECTIVE TISSUES. 
 
 15. This term is applied to various kinds of tissue that 
 bind together and support the other tissues of the body. 
 They vary very much in appearance in the fully formed 
 condition, but when we study their origin they are found 
 to spring from a tissue that has always the same general 
 characters, sortie of which will be afterwards described. 
 Thus we find that bone, cartilage, the tissue that forms 
 tendons or sinews, the tissue forming the ligaments that 
 bind the bones together, the tissue that forms the fasciae 
 and sheaths of muscles already alluded to, the tissue cori- 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 33 
 
 taining the fat below the skin, and the tissue consisting of 
 fine fibres that forms a supporting structure in nearly all 
 the organs of the 
 body, must all be re- 
 garded as belonging to 
 the connective tissue 
 group. The soft parts 
 consist largely of this 
 kind of tissue. 
 
 OTHER SOFT TISSUES. 
 
 16. Distribute d 
 among the muscles and 
 the connective tissues 
 -already noticed, we 
 find blood-vessels, or 
 tubes for the distribu- 
 tion of blood, con- 
 sisting of arteries, 
 capillaries, and veins. 
 We also find numerous 
 nerves. These soft 
 tissues will be fully 
 described when we 
 consider the circula- 
 tion of the blood, 
 nutrition, and the 
 functions of the 
 nervous system (fig. 
 28). 
 
 d. THE SKIN. 
 
 17. Clothing the 
 surface of the body, 
 we find the skin, 
 
 Fig. 28. — A, superficial, and B, deep, 
 
 dissected view of Left Artn : 
 veins; b, h, nerves; c, fascia or membrane; 
 dt biceps : e^ brachial artery ; f, radial artery ; 
 gi ulnar artery ; h^ arteries in palm. 
 
 This organ consists of certain layers, 
 C 
 
34 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 to be afterwards described, and it is richly supplied 
 with minute blood-vessels and with nerves. The skin 
 protects the parts situated beneath it; it contains the 
 organs by which we appreciate contact or touch; it con- 
 tains also certain glands that secrete the sweat and the 
 oily substance called sebaceous matter, and it has important 
 functions in connection with the regulation of the tempera- 
 ture of the body. At certain places, such as the openings 
 of the mouth and nostrils, the anus, and the opening of the 
 urinary passages, the skin becomes continuous with the 
 membrane that lines the alimentary canal, the respiratory 
 and other passages. 
 
 e. MUCOUS MEMBRANES. 
 
 1 8. These are thin membranes lining passages and 
 cavities that communicate with the exterior. They are 
 covered or protected by a somewhat viscid or sticky fluid 
 termed mucus. Such a membrane always consists of a 
 layer of connective tissue covered with one or more layers 
 of cells known as epithelial cells, and thus it follows that no 
 foreign substance can pass into the tissues of the body, say 
 from the cavity of the stomach or bowels, without passing 
 through such a layer of epithelium. The chief mucous 
 membranes are the gastro-fulmonary a,w6i the genito-urinary. 
 The gastro-pulmonary lines the alimentary canal from the 
 mouth to the anus, and it also extends into the air passages 
 and lungs, lining the windpipe, bronchial tubes, and air- 
 cells in the lung, where the respiratory exchanges between 
 the blood and the air take place. The respiratory mucous 
 membrane passes also from the interior of the nose into 
 the tear ducts or lachrymal passages, and it covers the 
 front of the eyeballs and lines the eyelids under the name 
 of the conjunctiva. From the back of the throat the 
 membrane passes into the Eustachian tube, a canal com- 
 municating with the middle ear or tympanum. Lastly, 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 35 
 
 the gastric mucous membrane lines the ducts" of all the 
 secreting glands that open into the alimentary canal, such 
 as the salivary glands, the pancreas, and the liver. 
 
 19. The genito-urinary mucous membrane passes from 
 the orifice of the urethra, or opening of the urinary passage, 
 through the urinary tract to the bladder, and from thence 
 through the ureters to the kidneys, and it also lines the 
 generative passages of the female. The minute structure 
 of mucous membranes will be further described. 
 
 Questions. 
 
 13. 16. What tissues form the so- called _/?«j^ of a limb ? 
 
 14. Give an example of each of the different kinds of muscles. De- 
 
 scribe the movements of pronation and supination. 
 
 15. What do you understand by connective tissue? 
 
 17, What glands occur in the skin ? 
 
 18. What is a mucous membrane? Describe the general distribution 
 
 of the gastro-pulmonary mucous membrane. 
 
 0. THE INTERNAL ORGANS. 
 
 20. The body without the limbs is divided into the trunk 
 and head. These are cavities containing certain internal 
 organs. The cavity of the head contains the brain. The 
 trunk is subdivided into the thoracic, abdominal, and pelvic 
 cavities. The thoracic cavity, usually called the chest, 
 contains the trachea or windpipe, the lungs, the heart, the 
 oesophagus or gullet, and the great blood-vessels entering 
 into and issuing from the heart (fig. 29). A membranous- 
 muscular partition, the diaphragm (O, fig. 29), separates 
 the thoracic cavity from the abdominal cavity. The 
 abdominal cavity contains the stomach, liver, gall-bladder, 
 spleen, pancreas, kidneys, and small and large intestines, 
 &c. (fig. 29). The pelvic cavity contains the bladder, 
 rectum or lower bowel, and the generative organs. 
 Another mode of gaining a conception of the cavities of 
 the body is to suppose it to be divided by a vertical 
 
36 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 plane passing through the bodies of the vertebrae from 
 the base of the skull downwards (fig. 30, A). The body 
 is thus divided into anterior and posterior cavities. The 
 posterior cavity in the head contains the brain, while the 
 anterior is represented by the cavities of the mouth and 
 
 Fig. 29. — Contents of the Chest and Abdomen : 
 
 O, diaphragm ; C, heart ; A, B, lungs ; N, windpipe ; P, liver ; R, spleen ; 
 
 S, stomach ; W, W, small intestine ; T, U, V, large intestine. 
 
 nose. In the trunk, the posterior cavity is occupied 
 by the spinal cord, while the anterior consists of the 
 cavities of the thorax, abdomen, and pelvis. With 
 the exception of the cavities of the mouth and nose, 
 which are the openings of the alimentary and respiratory 
 
GENERAL VIEW OP THE ANAtoMY OP THE B013Y. 37 
 
 systems respectively, the cavities are shut off from direct 
 communication with the exterior, and each is lined by a 
 thin serous membrane (so called because it secretes a 
 watery fluid like that 
 found after blood has 
 clotted), which is re- 
 flected over the surfaces 
 of most of the organs 
 contained in the cavity. 
 The serous membrane 
 consists of a thin layer of 
 connective tissue covered 
 by a single layer of flat- 
 tened cells. A small 
 amount of a watery fluid 
 is secreted or formed by 
 these cells, thus moisten- 
 ing the surface and 
 diminishing friction when 
 the inner surface of the 
 wall of the trunk touches 
 or rubs against the outer 
 surface of the organs Fig- 30.— (A) Vertical and (B) Trans- 
 contained in the cavity. ""^^ Sections of the Human Body : 
 
 The cavities of the "' '''"" ' '' *' ''='■'='"■=« '' ^> '''^'" = '^' =p'"^' 
 ine cavities OI me cord; «, abdomen ;y;/y^ digestive system; 
 
 body contain important *, heart ; k, sympathetic nervous system ; 
 . i_ „ 1 • »/, mouth ; t^ chest. 
 
 organs, the general post- ' 
 
 tion of which and their relation to other parts should be 
 
 known before we proceed to consider their functions. 
 
 Questions. 
 
 20. Enumerate the organs found in the thorax Enumerate the organs 
 found in the abdomen. Make a drawing showing what may be 
 seen in a transverse section of the body. 
 
38 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 1. THE CENTRAL NERVOUS ORGANS. 
 
 21. The central nervous system is sometimes called the 
 cerebrospinal axis, and is contained partly within the cavity 
 of the cranium, and partly within the canal formed by the 
 rings of the vertebrae called the vertebral canal (see figs. 
 3 and 30). It is divided into the large mass placed 
 in the cranium called the brain, and the spinal cord 
 within the vertebral canal. Both the brain and spinal cord 
 consist of a right and left half, which are symmetrical and 
 very similar in structure to each other, each half being 
 connected with the other by bands of nervous matter, so as 
 to form one complete organ. The brain and cord are 
 protected by the bony walls of the skull and vertebral 
 column, and they are surrounded by three membranes 
 which give additional protection and aid in the nutrition of 
 the organs. 
 
 22. The spinal cord or spinal marrow is in the vertebral 
 canal, extending from the margin of the foramen magnum of 
 the occipital bone to the lower part of the body of the first 
 lumbar vertebra. Above, it is continuous with a part of the 
 brain called the medulla oblongata or bulb, and below it ends 
 in a long slender filament. The cord lies in the canal sur- 
 rounded by sheaths, and from its sides issue the thirty-two 
 pairs of spinal nerves, each nerve having an anterior and a 
 posterior root. The length of the cord in an adult is from 
 fifteen to eighteen inches (fig. 30, c, d). 
 
 23. The brain, sometimes called the encephalon, is situ- 
 ated within the cranial cavity, and it is divided into the 
 medulla oblongata or bulb, the pons, the cerebellum, and the 
 cerebrum. The bulb is the lower part, continuous with 
 the upper end of the cord, and lying on the lower part 
 of the occipital bone, within the foramen magnum (see 
 fig. 11). The cerebellum occupies the hindermost fossa or 
 depression in the base of the cranium. It is connected 
 
GENERAL VtEW OF THE ANATOMY OF THE BODV. 39 
 
 below with the bulb, above with the cerebrum, and in front 
 with the pons. The pons is a bridge-like mass of nervous 
 matter above the bulb, and related to the two halves of the 
 cerebellum, while nerve fibres pass upwards and downwards 
 connecting the bulb with the cerebrum. 
 
 24. The cerebrum is the largest part of the brain, and 
 occupies the space represented by the vault of the skull. 
 It consists of two hemispheres, the surfaces of which show 
 folds called the convolutions, and its internal structure shows 
 certain cavities and enlargements which it is not necessary 
 here to describe. (For illustrations of brain, see Nervoits 
 System.) The brain is protected by membranes, and it is 
 richly supplied with blood. 
 
 II. the organs of digestion. 
 
 25. These form a long canal, the alimentary canal, ex- 
 tending from the mouth to the anus. It is situated in front 
 of the vertebral column, commences at the face, passes 
 through the neck and chest, enters the abdominal cavity, 
 in which the chief digestive organs are situated, and ends 
 at the outlet of the pelvis, in front of the coccyx, by the 
 anal orifice. In its upper part the alimentary canal is 
 related to the organs of respiration, and in the lower to the 
 genito-urinary apparatus. The canal is in length from 
 seven to eight times that of the individual, while its diam- 
 eter is not the same throughout, being in some places con- 
 tracted to a tube, and in others dilated into a sac or bag. 
 The upper part, above the diaphragm (the musculo-mem- 
 branous partition between the chest and abdomen), through 
 which the food passes to the stomach, is straight ; and the 
 part below the diaphragm is much convoluted, becoming 
 again straight near its termination (fig. 29). The part above 
 the diaphragm includes the mouth, the pharynx, and the (eso- 
 phagus or gullet (fig. 31). The part below the diaphragm 
 is formed by the stomach, the small intestine, subdivided 
 
40 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 into the duodenum, the jejuimm, and ileum, and the large 
 intestine, which is composed of the ccecum, the colon, and 
 the rectum. Connected with the alimentary canal we find 
 certain glandular organs, the chief of which are the salivary 
 
 Fig. 31. — Section through Mouth, Nose, &c. ; 
 
 a, sphenoid bone ; ^, Eustachian tube ; f, soft palate ; d, uvula ; e, nasal 
 
 passage ; y, upper jaw ; ^, lower jaw ; h^ epiglottis ; w, mouth. 
 
 glands, the ducts of which open into the mouth, the liver 
 and pancreas, related to the duodenum, and numerous glands 
 found in the mucous membrane of the bowel itself. 
 
 26. The mouth is at the entrance of the digestive canal. 
 It pccupies the lower part of the face, and is situated 
 between the two jaws, below the nose, between the cheeks, 
 behind the lips, and in front of the pharynx (fig. 31). It is 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 4t 
 
 concerned in tasting by the tongue, chewing or masticating by 
 the jaws and teeth, insalivation by the saUva formed by the 
 sahvary glands, and in articulate speech. The roof of the 
 mouth is formed in front by the hard palate, behind by the 
 soft palate, and its floor is constituted by the tongue and 
 soft parts. From the soft palate two pillars pass down to 
 the back part of the tongue on each side. The posterior 
 orifice of the mouth is 
 the opening of \ht fauces 
 or throat. Its sides are 
 formed by the pillars of ' 
 thefauces,]\i5t mentioned, 
 the floor by the base of 
 the tongue, and the roof 
 by the posterior border 
 of the soft palate, with 
 the uvula in the centre. 
 Between the pillars of 
 the fauces lie the tonsils. 
 These are small gland- 
 like structures. 
 
 27. In the floor of the 
 mouth we find the tongue 
 (fig. 32, 12), an organ 
 concerned in touch, taste, 
 mastication, and speech. 
 It will be afterwards 
 more fully described. 
 
 28. The lining membrane of the mouth contains numer- 
 ous small glands, the labial (lips), buccal (cheeks), and 
 palatine (palate) glands. There are also six large glandular 
 organs, three on each side, named the parotid, submaxil- 
 lary, and sublingual glands. The parotid is situated 
 below and in front of the lobe of the ear, behind the 
 edge of the ascending part of the lower jaw (fig. 32, 1). 
 
 Fig. 32.— The Salivary Glands : 
 
 the parotid gland ; 2, the submaxillary 
 gland; 3, the sublingual glnud; 4, Steno's 
 duct ; s, Wharton's duct ; 6, Bartholin's 
 duct ; 7, masseter muscle ; 8, mastoid pro- 
 cess ; 9, digastric muscle ; 10, internal jugular 
 vein; 11, external carotid artery; 12, the 
 tongue. 
 
42 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 Its duct, called the duct of Stem, opens into the mouth 
 between the first and second molar teeth in the upper 
 jaw, 4. The submaxillary gland, =, is situated just behind 
 the body of the lower jaw and its duct, known as the 
 duct of Wharton, opens into the mouth by a very narrow 
 orifice below the tongue and behind the incisor teeth 
 of the lower jaw, s- The sublingual gland, 3, consists 
 
 Fig. 33. 
 
 Microscopic structure of A, a mucous, and B, a serous salivary gland. 
 
 For description see text. 
 
 of a group of small glands found below the tongue and 
 its excretory ducts, called the ducts of Rivinus, seven or 
 eight in number, open in the loose tissue below the tongue. 
 The largest of these is called the duct of Bartholin. 
 
 The salivary glands differ in the characters of their secretion 
 and also in their structure. When the secretion is thick and 
 mucous-like, as we find in the fluid flowing from the ducts of the 
 sublingual gland, the gland is called a mucous gland ; but when 
 it is thin and watery, as is the case with the fluid flowing from 
 the parotid gland by Steno's duct, the gland is said to be a 
 serous gland. The little pouches of both kinds of glands are 
 lined with living secreting cells. The cells secreting a mucous 
 fluid, as in fig. 33, A, are large and clear, while those secreting 
 a serous fluid are very granular, as in fig. 33, B. Mucous 
 glands have also peculiar cells, like half-moons, adhering to 
 the side of the pouch (fig. 33, A, b). The ducts are lined with 
 columnar cells (fig. 33, B, c). 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 43 
 
 29. The pharynx is a muscular and membranous bag 
 which forms a space common to the digestive and respira- 
 tory passages be- 
 tween the cavities of 
 the mouth and nose 
 on the one hand 
 and the oesophagus 
 and larynx on the 
 other (fig. 31). It 
 changes its form both 
 in swallowing and 
 in the production 
 of voice. Opening 
 from the pharnyx we 
 find the (esophagus or 
 gullet, a tube passing 
 from the pharynx 
 into the stomach 
 (fig. 34, e). It runs 
 through the neck and 
 the thorax, and passes 
 through the dia- 
 phragm to terminate 
 in the stomach. When 
 at rest, the anterior 
 and posterior walls of 
 the oesophagus are 
 in contact, and dur-"' 
 ing swallowing the 
 bolus or mass of food 
 dilates successive 
 portions as it passes along. 
 
 30. We now reach the stomach, a dilatation of the alimen- 
 tary canal between the oesophagus and the duodenum. It 
 fills the upper part of the abdominal cavity. It lies below 
 
 Fig. 34. — Diagram of Digestive Organs : 
 a, salivary glands ; d^ pharynx ; c, windpipe ; d, 
 vein ; e^ gullet ; /, thoracic or chyle duct ; ^, 
 spleen ; A, stomach ; z, pylorus ; ky liver ; /, gall- 
 bladder ; m^ duodenum ; n, pancreas ; o, large 
 intestine ; p, small intestine ; r, absorbents ; f, 
 vermiform appendix. 
 
44 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 the diaphragm, and is separated by it from the heart. To 
 the right of the stomach lies the liver, an organ which over- 
 laps the stomach to some extent. In front the stomach is 
 
 covered by the wall 
 of the abdomen, 
 where there is a well- 
 known depression — 
 ihcepigastrium. This 
 depression, some- 
 times called the pit 
 of the stomach, often 
 contains a part of 
 the liver, while the 
 stomach lies lower 
 down, and is below 
 the lower point of 
 thebreast-bone. The 
 
 Fig. 35. — Section of the Stomach : 
 
 a^ ducts of liver ; ^, pylorus ; c, bile-duct ; 
 
 d^ pancreatic duct ; «, cardiac orifice. 
 
 great end of the stomach, to the left, is in contact with the 
 spleen. 
 
 31, We next pass on to the intestines, which are divided 
 into the small and the large, according to their calibre. 
 The small intestine includes that part of the alimentary 
 canal between the stomach and the great intestine, and it is 
 divided into three portions — the duodenum, jejunum, and 
 ileum. The duodenum, about ten inches in length, begins 
 at the pyloric aperture of the stomach, to the right of the 
 first lumbar vertebrae, forms a bend which grasps the head 
 of the pancreas, and ends in the jejunum at no very precise 
 point (figs. 35 and 37). The jejunum and ileum, together 
 about twenty feet in length, fill almost the whole of the 
 abdomen, and this portion of the small bowel is almost 
 surrounded by the large intestine (fig. 29). The large intes- 
 tine, divided intd the cmciim, colon, and rectum, is from 
 four to five feet in length, and commences in the right 
 iliac region (or portion of the abdomen a little above 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 45 
 
 the groin on the right side), passes upwards to the right 
 
 hypochondrium (lower border of the ribs), then, having 
 
 reached the liver, it makes a bend and runs transversely 
 
 from right to left to the left hypochondrium, below 
 
 the position of the spleen ; there again it makes a 
 
 sharp bend, becomes vertical, and runs down to the 
 
 left iliac region, where, after twice bending on itself, 
 
 like the letter S, it dips into the pelvis and ends at the 
 
 anus. The first part, the ccecwn, 
 
 lies in the right iliac region, and 
 
 between it and the last part of 
 
 the small intestine, the ileum, 
 
 there is a valve, the iko-ccecal valve, 
 
 which prevfints matters from 
 
 passing backwards from the large 
 
 to the small intestine (fig. 36). 
 
 Connected with the caecum there is 
 
 a small narrow tubular structure, 
 
 like an earthworm, known as the 
 
 appendix vermiformis. The colon 
 
 constitutes the greater part of 
 
 ,, i • i i- i J' Fig. 36. — Caecum inflated, 
 
 the great mtestme, extendmg % . , , j » u 
 
 " ' ° dried, and opened to show 
 
 from the caecum to the rectum, the arrangement of tlie 
 and it is usually divided into the valve : 
 
 ascending or right lumbar colon, "• termination of the ileum ; b, 
 
 , J- , ascending colon ; .:, c£cum ; rf, 
 the transverse colon or arch of the ^ transverse construction project- 
 
 Colon, and the descending colon '"g into the caecum ; e/, lIps of 
 
 . , , . -7/7 T 1 ^'^ valve separating the small 
 
 With the sigmoid flexure. Lastly, f„,„ the large intestine : e, ver- 
 
 we find the rectum, situated in the miform appendix of the caecum. 
 
 pelvis and in front of the sacrum and coccyx. 
 . 32. We have now shortly to consider the position of the 
 great glands associated with the alimentary canal. The 
 chief of these is the liver, which is the largest gland in 
 the body. It lies near the duodenum, below the six 
 lower ribs op the right side, and separated from the 
 
46 ELEMENTARY HUMAN PHYStOLOGY. 
 
 organs in the thorax by the diaphragm. It is an irregu- 
 larly shaped organ, divided into lobes, weighing in the 
 adult from three to four pounds, and measuring in its 
 longest diameter, the transverse, from ten to twelve inches. 
 It is from four to five inches from above downwards, and 
 about six or seven inches thick, from before backwards. 
 Connected by membranous folds with the wall of the body, 
 it is capable of a small amount of movement, as in inspira- 
 tion and by change of posture. Its excretory apparatus 
 consists of the hepatic duct or true bile duct, the gall- 
 bladder, with its duct called the cystic duct, and a duct 
 
 Fig. 37. — Relations of Liver and Pancreas to Intestine : 
 <;, u^ liver ; 3, gall-bladder ; r, duodeniini ; d^ pancreas ; f, spleen. 
 
 known as the common bile duct, formed by the union of the 
 cystic duct with the hepatic duct (fig. 37). The gall- 
 bladder is a reservoir for the bile, lying on the under surface 
 of the right lobe of the liver, in form like that of a pear, so 
 placed that its broad end looks forwards, downwards, and 
 to the right, and its small end backwards, upwards, and to 
 the left. The common bile duct opens into the duodenum 
 (fig. 37). 
 
 33. The pancreas is an elongated gland situated trans- 
 versely and deeply behind the stomach, and in front of the 
 lumber vertebrae. In order to see it, the stomach must be 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 47 
 
 turned upwards. It is an oblong body, flattened from 
 before backwards, wider at the right end than at the left. 
 The head lies in the centre of the duodenum, while the 
 tail touches the spleen. It weighs from three to four 
 ounces. Behind the pancreas there are several structures 
 separating it from the vertebral column — namely, portions 
 of the diaphragm, the great vein (vena cava) on the right 
 side, and the aorta on the left. To the left of the spine 
 the pancreas is near the left kidney. The duct of the 
 pancreas runs through the substance of the gland, from the 
 tail to the head, and joining the common bile duct, opens 
 into the duodenum (fig. 37, d). 
 
 34. The spleen is a spongy soft organ placed behind and 
 to the left of the great end of the stomach (fig. 37, e). 
 It has no duct This organ, as will be hereafter explained, 
 is concerned in the formation and purification of the blood. 
 
 III. THE ORGANS OF RESPIRATION. 
 
 35. These consist of (i) the lungs, situated in (2) the 
 thorax or chest, a cavity having its walls capable of ex- 
 panding and contracting, thus forming a kind of bellows ; 
 and (3) a tubular arrangement by which the air spaces in 
 the lungs communicate with the external air, comprising 
 the nasal fossce, the pharynx, the larynx, the trachea or 
 windpipe, and the bronchi or bronchial tubes. 
 
 36. The thorax has been already described (see p. 19). 
 Th^ pharynx, also described at p. 43, is common to both 
 the digestive and respiratory passages. The nasal fossce, 
 or nares, are the passages by which the air enters the 
 respiratory organs, and they are also the seat, in their upper 
 parts, of the sense of smell (fig. 31). 
 
 37. The lungs, two in number, occupy the thoracic 
 cavity, and are placed on each side of the heart (fig. 29). 
 Their size corresponds exactly with the capacity of the 
 thorax, their outer surfaces being always in close contact with 
 
4-8 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 the inner surfaces of the chest wall. The surface of the lung 
 is covered with a fine serous membrane which is reflected 
 over the inner surface of the wall of the chest. Two 
 serous membranes, the layers of the pleura, are thus in 
 contact, and the space between them (which in health can 
 scarcely be said to exist, seeing both surfaces are in con- 
 tact) is called the pleural cavity. Each lung is shaped like 
 a cone, deeply depressed on the inner side, with the apex 
 above and the base below. The left lung is divided into 
 two lobes, a superior and inferior ; and the right into three 
 lobes, a superior, middle, and inferior. The inferior lobe 
 of each lung forms the base, and the base is concave, 
 moulded on the convexity of the diaphragm. The superior 
 lobe forms the apex, which projects into the neck above the 
 first rib. The inner surface of each lung shows what is 
 called the root of the lung, that is, the part at which it com- 
 municates with the trachea, through the bronchi, and by 
 which blood-vessels enter into and issue from the lung. 
 Behind the root there is a space called the posterior 
 mediastinum, in which we find, on the left side, the 
 descending aorta, upper part of the thoracic duct, and 
 left vagus nerve, and on the right side the azygos vein, 
 the oesophagus, the lower part of the thoracic duct, 
 and right vagus nerve. In front of the root we find 
 another space, called the 7niddle mediastinum, in which 
 the heart rests. 
 
 38. The trachea, or windpipe, is the tube passing from 
 the larynx to the air tubes in the lungs, or bronchi. From 
 four to five inches in length, it extends from about the 
 level of the fifth cervical to the third dorsal vertebra, 
 almost in the median line of the neck, and it divides below 
 into the two bronchial tubes (fig. 38). Near its upper 
 end it is covered by a gland called the thyroid glatid; an 
 important artery, the comvion carotid artery, and a nerve 
 palled the vagus or prieuniogastric, are in contact with it 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 49 
 
 on either side. The trachea is flattened behind, and lies 
 almost in front of the oesophagus (see fig. 34). In the 
 thorax, it lies in the space extending up from the root of 
 the lung called the superior mediastinum ; behind it, we find 
 the oesophagus, which separates it from the spinal column, 
 and it is surrounded by many 
 glands and vessels and loose 
 connective tissue. It divides 
 into the right and left bron- 
 chus, tubes passing one to 
 each lung. These bronchi 
 divide and subdivide in the 
 lung, becoming smaller and 
 smaller, as will be afterwards 
 described. 
 
 39. The larynx is a box 
 formed of various pieces of 
 cartilage movable on each 
 other. It is in the middle 
 line of the neck, opening into 
 the pharynx above and into 
 the trachea below. It is the 
 upper end of the respiratory 
 tube, and specially concerned 
 
 in the production of voice, windpipe and "one of the Lungs : 
 The larynx is very prominent „, windpipe ; b, bronchi ; 
 
 in the throat of the male, ^, bronchial tubes. 
 
 forming the pomum Adami, or Adam's apple ; in the 
 female it is smaller. The differences in size affect the 
 pitch of the voice in the two sexes (fig. 31), 
 
 IV. THE GENITO-URINARY ORGANS. 
 
 40. These consist of two secreting glands called the 
 kidneys ; two ducts, the ureters; a reservoir for the urine, 
 the bladder; and an excretory canal, the urethra. 
 
 D 
 
 Fig. 38. 
 
so ELEMENTARY HUMAN PHYSIOLOGY. 
 
 41. The kidneys, of well-known form, are deeply placed 
 in the lumbar region, one on each side of the vertebral 
 column. They are usually cov- 
 ered with fat, and are connected 
 with vessels which enter and emerge 
 from them. Each kidney is from 
 three and a half to four inches in 
 length, two inches in breadth, and 
 one inch in thickness, weighing 
 from two to four ounces. The 
 right kidney is a little lower than 
 the left, owing to the presence of 
 the liver, by which it may be 
 covered. It may also touch the 
 gall-bladder. On the right side, 
 the kidney is also in close relation 
 with the duodenum. On the left 
 side, the kidney is near the spleen 
 and the great end of the stomach. 
 The structure will be afterwards 
 described. The duct that carries the urine from the 
 kidney is called the ureter, passing from the concave side 
 of the kidney to the bladder. It is about the thickness of 
 a crow's quill. It runs down to the level of the base of 
 the sacrum, where it enters the bladder. 
 
 Immediately above each kidney there is a small gland, 
 having no duct, known as the suprarenal capsule. These 
 bodies have to do with the elaboration of the blood. The 
 bladder lies in the pelvis, in the middle line, behind the 
 pubis. When empty it lies in the pelvis, but it rises into 
 the abdominal cavity as it fills. It is oval in form, the 
 great end being directed upwards. The anterior wall is 
 behind the symphysis pubis ; the posterior wall, in the 
 male, is in front of the rectum, and in the female in front 
 of the uterus, or womb. 
 
 Fig. 39. 
 
 •Urinary Apparatus : 
 
 Uj inferior vena cava ; b^ h 
 
 kidneys ; c, aorta ; d^ ureter 
 
 e, bladder. 
 
GENERAL VIEW OF THE ANATOMY OF THE BODY. 51 
 V. THE ORGANS OF THE CIRCULATION. 
 
 42. These consist of the heart, arteries, capillaries, and 
 veins. The general position of the heart has already been 
 indicated (pp. 36 and 47), and the arrangement of the 
 organs of the circulation will be best considered when 
 we discuss the circulation of the blood. 
 
 Questions. 
 
 21. Describe the general position in the body of the cerebrospinal 
 
 axis. 
 
 22. What do you mean by spinal cord and medulla or bulb ? What 
 
 is the connection of the spinal nerves with the spinal cord ? 
 
 23. What are the parts of the encephalon ? 
 
 25, 26. Describe the parts forming the mouth and found in the mouth. 
 
 26. Describe what you see if you open your mouth wide before a 
 
 looking-glass. 
 
 28. Describe the position and ducts of the salivary glands. Make a 
 
 drawing showing the different appearances of a mucous and a 
 serous gland. 
 
 29. Give an account of the pharynx, showing its position and the 
 
 openings communicating with it. Show by a drawing the 
 position in the neck of the trachea and oesophagus. 
 
 30. Make a drawing of the shape of the stomach. 
 
 31. Give a short account of the position of the different parts of the 
 
 alimentary canal. What and where is the ileo-ctecal valve? 
 What is its use? Where is the appendix vermiformis ? 
 
 32. Give an account of the position of the liver. What are its ducts ? 
 
 Where is the gall-bladder ? 
 
 33. What is the position of the pancreas ? 
 
 35 1 36> 37- What do you understand by the pleural cavity? 
 38. What is the origin, course, and mode of termination of the trachea ? 
 41. Give an account of the position and relation to other organs of the 
 two kidneys. 
 
52 
 
 CHAPTER II. 
 
 CHEMICAL CONSTITUTION OF THE BODY, AND THE 
 CHEMICAL ACTIONS OCCURRING IN IT. 
 
 In connection with this department of physiology, we 
 shall briefly discuss (i) the chief elementary constituents of 
 the human body; (2) the chief compounds which have 
 been isolated by the chemist ; and (3) the chief chemical 
 changes which occur in the living organism. 
 
 43. If the body, or a portion of it, were submitted by a 
 chemist to complete analysis, it could be resolved into the 
 chemical elements of which it is composed, or into compounds 
 formed by certain of those elements. By an element is 
 meant a substance that cannot be further decomposed by 
 any means at present known to the chemist. Thus carbon, 
 oxygen, hydrogen, and nitrogen are elements. By no 
 known means can carbon be resolved into other bodies ; 
 and the same remark applies to all elements. Sixty-nine 
 or seventy elements are known to exist, and of these not 
 more than eighteen or twenty have been found in living 
 matter. Chief among these are the four already named 
 — carbon, oxygen, hydrogen, and nitrogen. Carbon at 
 ordinary temperatures is a soUd. The other three exist 
 in ordinary circumstances as gases ; but at very low tem- 
 peratures, and under great pressure, they also may pass 
 into the liquid, and finally into the solid state. Oxygen 
 unites readily with hydrogen, carbon, and nitrogen, to form 
 compounds ; hydrogen and carbon do not unite with other 
 substances readily at ordinary temperatures ; and nitrogen 
 is remarkable for its inertness — that is to say, it does not 
 unite readily with other bodies, and the compounds it 
 forms are not very stable, but are liable to decomposition. 
 Seeing that no matter can exist in the living state that 
 
Chemical constitution op the body. 53 
 
 does not contain nitrogen, and that living matter is chemi- 
 cally in a state of constant flux or change, the loose bonds 
 that nitrogen forms with other substances may explain the 
 instability and tendency to change so characteristic of 
 living matter. 
 
 ELEMENTARY CONSTITUENTS. 
 
 44. The principal elementary constituents, then, are car- 
 bon, oxygen, hydrogen, and nitrogen. Those next in 
 importance, or at all events in frequency, are sulphur, 
 phosphorus, chlorine, sodium, potassium, calcium, and iron. 
 The first four are met with in all the fluids and solids of 
 the body ; sulphur in albuminous matters, blood, and in 
 most secretions ; phosphorus in blood, nervous matter, 
 bone, the teeth, and in most liquids ; fluorine in bone and 
 the teeth ; chlorine everywhere ; sodium everywhere ; potas- 
 sium in the muscles, coloured blood-corpuscles, nervous 
 matter, and secretions ; calcium in bone, teeth, and fluids ; 
 magnesium usually accompanies calcium ; iron in the 
 colouring matter of the blood, bile, urine, &c. The rarer 
 bodies are silicon, lithium, manganese, copper, and lead. 
 It is interesting to classify these substances — the bricks 
 of which the edifice is composed — according to the 
 method of the chemist. Thus, of the hydrogen group, we 
 find hydrogen and chlorine ; of the oxygen group, oxygen 
 and sulphur ; of the nitrogen group, nitrogen and phos- 
 phorus ; of the carbon group, carbon and silicon ; of the 
 alkaline bodies, sodium and potassium ; of the alkaline earths, 
 calcium and magnesium ; and of the metals, only one, iron. 
 Of fifteen non-metals, nine are represented ; while of the 
 fifty-four metals, only one, iron, is indispensable, and other 
 three or four may be present — namely, manganese, copper, 
 and lead. The earth's crust consists chiefly of oxygen, 
 silicon, aluminium, iron, calcium, magnesium, sodium, and 
 potassium ; water is formed of oxygen and hydrogen ; and 
 
54 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 living matter contains all of these elements, with several 
 in addition. 
 
 COMPOUNDS. 
 
 45. The elements are so combined in living matter as 
 to constitute compound bodies, which may be separated as 
 such by chemicat processes. Such compounds are termed 
 proximate principles. For example, phosphate of lime is a 
 proximate constituent of bone, but phosphoric acid and 
 oxide of calcium, which together form phosphate of lime, 
 do not exist individually in bone. Chief among these 
 proximate constituents is water. There are two classes of 
 compounds : Inorganic, such as water and phosphate of 
 lime, and organic, such as albumin and urea. 
 
 Inorganic Compounds. 
 
 46. These may be divided into water, inorganic acids, 
 inorganic bases, and salts. 
 
 Water forms about two-thirds of the weight of the body, 
 so that a body weighing about 165 lb. will contain about 
 no lb. of water. Certain tissues contain very little 
 water, such as the substance of tooth, bone, &c. ; whereas 
 others, such as brain-matter and muscles, contain a great 
 amount. 
 
 Inorganic Acids. — These are hydrochloric, hydrofluoric, 
 phosphoric, sulphuric, and silicic. None of these occur in 
 the free state (except the first in the juice of the stomach), 
 but are combined with sodium, potassium, calcium, &c. 
 One of the most important substances belonging to this 
 group is carbonic acid. It is formed by a union of carbon 
 with oxygen, and at ordinary temperatures and pressures 
 it is a colourless gas. It can be liquefied and solidified 
 by pressure or cold, or by both combined. Carbonic acid 
 is one of the chief products of combustion or burning, the 
 carbon of the substance uniting with the oxygen of the air. 
 
CHEMICAL CONSTITUTION OF THE BODY. 55 
 
 It is also formed in large quantity by all living tissues, 
 whether of plants or animals. All living matter breathes — 
 that is to say, it takes in oxygen, and this gas unites with 
 the carbon of the tissues (many complicated chemical 
 processes occurring) to form carbonic acid, which is then 
 thrown out. If we blow air from the lungs into lime water, 
 the water becomes white and turbid from the formation of 
 carbonate of lime by the carbonic acid of the breath 
 uniting with the lime in the lime water. The air contains 
 about -04 volumes per cent, of carbonic acid — that is to say, 
 in 100 volumes of ^ir we would find, not one volume, but 
 Y^th of one volume. Thus loo cubic inches would contain 
 ^th of a cubic inch. Carbonic acid also exists in water of 
 rivers and springs (more especially the latter) and in the 
 ocean. The gas in the air is decomposed by the green 
 colouring matter of plants under the action of the sun's 
 rays, the carbon being built up into chemical compounds 
 forming the tissues of the plant, while the oxygen is liberated. 
 This must be distinguished from the true breathing process 
 of the plant, which is like that of animal tissues, oxygen 
 being taken in and carbonic acid given out. 
 
 Inorganic Bases. — These are soda, potash, ammonia, 
 lime, and magnesia. None occur free, but are combined 
 with acids to form salts. Ammonia is a compound com- 
 posed of nitrogen and hydrogen. Thus ammonium (the 
 base) consists of four volumes of hydrogen united with one 
 volume of nitrogen, and we may regard ordinary ammonia 
 as being formed of three of hydrogen with one of nitrogen. 
 Ammonia is a gas. It is readily soluble in water, and, 
 acting as a base, it forms salts, such as ammonium 
 phosphate, sulphate, and chloride, &c. As will be seen 
 later on, many complex organic bodies that contain nitro- 
 gen are bodies of the nature of ammonia, or rather they 
 are compound ammonias. The important fact to remember 
 is that it is from ammonia that the living matter in plants 
 
56 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 receives the nitrogen that is absolutely necessary for the 
 phenomena of vitaUty. In turn, the Uving matter of animals 
 receives its nitrogen from the nitrogen of plants. 
 
 Salts. — These are numerous, but the chief are chloride 
 of sodium, chloride of potassium, chloride of ammonium, 
 fluoride of calcium, phosphates of sodium and , potassium, 
 phosphate of calcium, phosphate of magnesium, and sul- 
 phates of sodium and potassium. The most important as 
 regards amount is the chloride of sodium, or common salt, 
 of which about 3086 grains, or over six ounces, exist in 
 an average human body. 
 
 Organic Compounds. 
 
 47. Such may be divided primarily into those containing 
 nitrogen, or nitrogenous, and those not containing nitrogen, 
 or the non-nitrogenous. The nitrogenous (grouped under 
 the name of proteids) include albumins, globulins, and 
 albuminoids. The non-nitrogenous include certain or- 
 ganic acids, animal sta,rch and the sugars, the fats, and 
 the alcohols. All proteids consist of carbon, hydrogen, 
 oxygen, nitrogen, and sulphur, and there are certain allied 
 substances containing phosphorus. The albumins com- 
 prise such substances as common albumin (familiar as 
 white of egg), found in blood, chyle, lymph, &c., and 
 casein, obtained from milk. The globulins, of which myosin, 
 in muscle, is an example, occur in muscle, blood, &c. The 
 albuminoids are so termed because, while they have proper- 
 ties peculiar to each, they have certain general properties 
 resembling those of the albumins. The chief are gelatin, 
 obtained by boiling skin, sinew, &c. ; chondrin, got by 
 boiling cartilage ; and elastin, made by the prolonged boil- 
 ing of elastic tissue. There are other nitrogenous bodies 
 which do not form a constituent part of any tissue, but as 
 they are made in the economy by those chemical dissolu- 
 tions of more complex substances on which vital activity 
 
CHEMICAL CONSTITUTION OF THE BODY. 57 
 
 would seem largely to depend, they are always found either 
 in the solids or in the excretions. The chief are urea and 
 uric acid, two substances in the urine which will be after- 
 wards described ; leucin, iyrosin, cystin, and taurin, found 
 in bile; kreatin and kreatinin, existing in muscle-juice; 
 and lecithin and cerebrin, found in nervous matter. These 
 will be subsequently referred to in treating of the juices in 
 which they occur, 
 
 48. The non-nitrogenous substances, consisting of carbon, 
 oxygen, and hydrogen, in varying proportions, comprise 
 four different kinds of bodies — namely : 
 
 Organic Acids. — Certain organic acids, which are usually 
 united with bases forming salts. The chief of these are 
 carbonic, formic, acetic, propionic, butyric, palmitic, stearic, 
 oleic, lactic, oxalic, succinic acids, &c. 
 
 Carbo-hydrates. — These are bodies so called because they 
 consist of carbon united with hydrogen and oxygen in the 
 proportions in which these latter exist in water. Thus, take 
 starch as an example. Water is formed of hydrogen and 
 oxygen in the proportion of 2 to i, and we write H2O — that 
 is, hydrogen 2 and oxygen i. Starch is CjHjqOj — that is, 6 
 of carbon, with hydrogen and oxygen in the proportion of 
 2 : 1, or HjgOj -^ 5 = SHjO. Animal starch or glycogen has 
 the same chemical formula as common starch. It is found 
 in the liver and muscles, and also in the tissues of the em- 
 bryo. Of sugars there are four varieties to be met with in 
 the body : maltose (malt sugar), and glucose (grape-sugar), in 
 the alimentary canal; inosite (muscle-sugar — not a true 
 sugar), found chiefly in the heart ; and lactose (milk-sugar), 
 found in milk. 
 
 Fats. — Chemically considered, a fat is glycerin in which 
 one, two, or three of the atoms of hydrogen are replaced 
 by the radicle of a fatty acid. Thus the chemical repre- 
 sentation of glycerin is CgHgOg, and 3 of H's may be re- 
 placed by the radicle of a fatty acid. This radicle is a group 
 
S8 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 of atoms, such as CjgHgjO, existing in stearic acid. Take 
 ordinary beef fat. It consists chiefly of stearin, and stearin 
 is glycerin in which 3 of the H's are replaced by three 
 of the group (CigHg^O). This gives us C3H5(Ci8H350)303. 
 If stearin is boiled with an alkali such as soda, the alkali 
 unites with the fatty acid to form a soap, and glycerin is 
 set free. It is especially worthy of notice that a fat contains 
 bulk for bulk much more carbon in proportion to the 
 oxygen than a carbo-hydrate. Thus in starch we have 6 
 of carbon to 5 of oxygen, whereas in fat we have 57 to 6 — 
 that is to say, in starch the proportion of C to O is about 
 1:1, but in fat it is nearly 10 : i. To burn a given 
 weight of fat, therefore, more oxygen is needed than to 
 burn the same weight of starch. Carbonic acid will be 
 produced in both cases, but more with fat than with starch, 
 and, lastly, as heat is evolved by combustion, fat when 
 burned will give out much more heat than would be evolved 
 by burning the same weight of starch. All this is of import- 
 ance in considering the values of fat and starch in foods for 
 purposes of heat production. Of such compounds in the 
 body there are three — stearin, palmitin, and olein, which 
 are found in all fatty matter. Four or five pounds of fatty 
 matter may be found in a body of average size and weight. 
 
 Alcohols. — In the body only two compounds are known 
 which physiological chemists refer to this ^ow^— glycerin, 
 which is the basis of all the fats, and cholestrin, which 
 exists in bile, and in a solid state forms the chief con- 
 stituent of gall-stones. 
 
 Waste Bodies. — Numerous substances are thrown out of 
 the body as useless, which would be even injurious if they 
 were allowed to accumulate. Of these some are nitro- 
 genous, while others are non-nitrogenous. The chief 
 representative of the non-nitrogenous waste bodies is car- 
 bonic acid, already referred to ; and the most important of 
 the nitrogenous group is urea. 
 
CHEMICAL CONSTITUTION OF THE BODY. 59 
 
 49. Urea. — This body, found chiefly in the urine, is 
 met with in small amount in blood, and also in many 
 of the liquids and solids of the body. It is a crystalline 
 substance in the pure state. It is inodorous, and has a 
 bitterish saline taste. It is readily soluble in water. It 
 consists chemically of i atom of carbon, 2 of nitrogen, 4 
 of hydrogen, and i of oxygen, and chemists represent it 
 by the formula CNjH^O. The importance of urea arises 
 from the fact that it is the substance by which nearly the 
 whole of the waste nitrogen of the body is eliminated. The 
 amount of urea thrown out of the body is influenced chiefly 
 by the quantity of proteid taken in the food, and it is 
 interesting, therefore, to compare the percentage composi- 
 tion of such a proteid as the albumen of white of egg with 
 urea. Thus in two parts of 
 
 Carbon. Hydrogen. Oxygen. Nitrogen. Sulphur. 
 
 Proteid 53 7-3 23-04 15-53 1-13 
 
 Urea 20 6-6 26-67 46-67 
 
 Urea therefore contains about three times as much nitrogen 
 as proteid (15-53 x 3 = 46-59), or 100 parts (grains or 
 ounces) of urea contain as much nitrogen as 300 parts of 
 proteid. 
 
 CHEMICAL CHANGES IN THE LIVING ORGANISM. 
 
 50. A little reflection will at once indicate how difficult 
 it is to attempt to investigate the chemical changes occur- 
 ring in a living tissue or in a living being. True it is, we may 
 collect and analyse every excretion, we may examine the air 
 before and after breathing, and we may analyse the food, 
 and give such food as we think may vary the conditions of 
 the inquiry ; but these procedures throw little light on the 
 chemical compositions and decompositions in the tissues 
 and organs which we know do take place. Still, without 
 direct evidence perhaps, but supported by all the known 
 facts and justified by all analogies, we can say that in the 
 
6o ELEMENTARV HUMAN PHYSIOLOGV. 
 
 body the chemical changes may be classified as follows : 
 Oxidations, decompositions, reductions, syntheses, and fer- 
 mentation or zymolysis. 
 
 51. Oxidations. — These constitute the great majority of 
 the chemical changes occurring in the body. By oxid- 
 ation is meant the union with oxygen of one or more 
 constituents of a complex substance, so as, in most cases, to 
 form one less complex. Oxidations may go on step by step, 
 each gradation being simpler than the one immediately pre- 
 ceding it. Thus the terminal products of the oxidation of 
 albuminous substances are urea, water, and carbonic acid, 
 and of the fats, water and carbonic acid. By artificial pro- 
 cesses of oxidation the chemist has succeeded in producing 
 many simpler compounds, and thus he has imitated the pro- 
 cesses going on in the body. From albuminous matter he 
 has formed leucin, tyrosin, glycocoU ; and from uric acid, 
 urea, oxalic, and carbonic acids, &c. The agent in processes 
 of oxidation is, of course, oxygen introduced by respiration. 
 These processes seem to be essential to the production of 
 all vital actions. 
 
 52. Decompositions. — By decomposition is meant the 
 splitting up of a substance into two or more components, 
 the combined weight of which represents exactly that of the 
 compound. Thus one of the acid substances found in the 
 bile, taurocholic acid, splits up into taurin and cholalic 
 acid, and the sum of the atomic weights of the latter two 
 is exactly equal to that of the former. Some substances 
 lose one or more molecules of water, and thus become 
 chemically changed. For example, kreatin and kreatinin, 
 compounds found in muscle-juice, differ only by a molecule 
 of water. Such a process of abstracting water is called 
 dehydration. Recently it has been conjectured that some 
 processes occurring in the body are what the chemist 
 terms dissociation, by which is meant a decomposition 
 occurring at a certain temperature and pressure or tension, 
 
CHEMICAL CONSTITUTION OF THE BODY. 6 1 
 
 in which the substances which have been separated will 
 re-unite to form the primitive compound when the former 
 conditions as to temperature and pressure are re-established. 
 Thus the colouring matter of the blood, called haemoglobin, 
 united with oxygen in the lungs, becoming oxy-haemo- 
 globin, and gives up the oxygen again to the tissues, as the 
 blood circulates through these, again becoming haemo- 
 globin. 
 
 53. Reductions. — By the term reduction is meant the 
 removal of oxygen from a complex substance. It rarely 
 happens apparently in the animal body. 
 
 54. Syntheses. — The formation of compound bodies by a 
 process of building up or synthesis is less understood than 
 processes of, decomposition. Sometimes this process simply 
 consists of one of hydration — that is, a compound unites 
 with water to form a more complex body. Thus kreatin 
 combines with a molecule of water and becomes kreatinin. 
 Chemists have synthetically produced many of the sub- 
 stances formed naturally in the body, such as urea, hippuric 
 acid, taurin, sarcosin, kreatin, oxalic acid, succinic acid, 
 acetic acid, 8z:c., but little is known as to the steps by which 
 these bodies are formed in the body. 
 
 55. Ferment-like Actions, or Zymolysis. — A \xv.t. ferment is 
 a living organism that has a powerful effect on certain 
 kinds of matter, sphtting it up into simpler bodies, while 
 at the same time the organism constituting the ferment 
 grows and multiplies. The common yeast used in 
 breweries and distilleries is an example. Yeast consists of 
 minute vegetable organisms or cells, constituting a group of 
 the fungi, and known as Saccharomycetes cerevisice. These 
 cells live on the sugar in the wort, changing it into alcohol 
 and carbonic acid chiefly, although small quantities of other 
 substances are formed. Certain cells in the body, especi- 
 ally the cells of certain glands, also produce substances 
 which act like ferments, but the difference is that the sub- 
 
62 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 Stance formed by the cell is not alive, but in a peculiar 
 state of molecular activity. The substance thus formed in 
 living cells is called a zymogen, to distinguish it from a true 
 ferment. The zymogen, in certain circumstances, yields 
 a ferment-like body called an enzyme, and the action of 
 the enzyme is called zymolysis, to distinguish it from true 
 fermentation. During the process the enzyme does not 
 increase in quantity. Both ferments and enzymes are killed 
 by the temperature of boiling water, and even at a lower 
 temperature. Any substance that arrests or destroys 
 growth of living organisms, like corrosive sublimate or 
 thymol, will check fermentation, but will have no effect 
 on zymolysis. Many examples of zymolytic changes 
 occur in the body. The enzymes are produ(;ed by living 
 cells in certain glands. Thus we have ptyalin, the enzyme 
 of the saliva, formed in the salivary glands; pepsin, the 
 enzyme formed in the gastric glands of the stomach, &c. 
 Their chemical constitution resembles that of albuminous 
 matters, but they contain no sulphur. The following are 
 examples of such processes : (i) The transforrpation 
 of starch into dextrin and into glycose, produced by the 
 action of ptyalin and pancreatin, and also under the 
 influence of all albuminous matters, especially in the act 
 of decomposition ; (2) the transformation of fats into fatty 
 acids and glycerin, accomplished by a pancreatic enzyme ; 
 and (3) the transformation of albuminates into peptones, 
 or soluble modifications of proteids, as happens under the 
 action of the pepsin of the gastric juice and of a pancreatic 
 enzyme. For the accomplishment of zymolysis certain 
 conditions of moisture and temperature are required. 
 These conditions exist in the animal body, so that 
 the chemical transformations of food during the process 
 of digestion are due to the action of soluble enzymes. 
 Probably also, similar changes occur in the more obscure 
 processes of nutrition, and in the actions of certain glands, 
 
CHEMICAL CONSTITUTION OF THE BODY. 63 
 
 such, for example, as the liver, where apparently an enzyme 
 is formed which converts glycogen or animal starch into 
 sugar. 
 
 56. Instability of Organic Compounds. — Certain proxi- 
 mate principles are the same as those met with in the crust 
 of the earth, or in the water of oceans and rivers, such as 
 chlorides of sodium and potassium, sulphates of soda and 
 potash, phosphates of soda, potash, lime, and magnesia. 
 The proximate principles more characteristic of plants and 
 of animals are composed of carbon, hydrogen, and oxygen, 
 such as starches, sugars, fats ; or are formed of carbon, 
 hydrogen, oxygen, nitrogen, and sulphur or phosphorus, 
 such as albumin in white of egg and the gluten of flour. 
 Compounds formed of three elements only have, especially 
 in the dry condition, a considerable amount of stability ; 
 on the other hand, compounds containing four or more 
 elements are much less stable. They tend to fly to pieces. 
 They exist only within a limited range of temperature and 
 pressure, and under the action of bodies in a more active 
 state (the enzymes) the complex organic substance falls to 
 pieces, not resolving itself into its elements, but into simple 
 groups of elements. Thus egg-albumen may split up into a 
 large number of simpler bodies — leucin, tyrosin, &c. — and 
 these last into still simpler, until we reach water and urea. 
 This instability, or tendency to change, is one of the 
 essential conditions of life. A living body is continually 
 undergoing a series of chemical changes, of composition 
 and decomposition, building up and pulling down, as a 
 result of which there is an incessant renovation of the 
 molecules of the organism. Chemical changes are a neces- 
 sary condition of the action of living matter, or it may be 
 said that the living state is always associated with chemical 
 change ; part of the living matter dies, is decomposed (or 
 rather its decomposition is its death), and the dead matter 
 is then thrown out of the organism. New matter is added 
 
64 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 from without, and then there is a perpetual exchange be- 
 tween the organic or living world and the inorganic or 
 dead world, which may be termed a circulation of matter. 
 
 Questions. . 
 
 43. Describe the general characters of the chief elements of which the 
 
 body is composed. 
 
 44. Classify the chemical elements of which the body is composed. 
 
 45. What is understood by the term ' proximate principle ?' 
 
 46. What amount of water occurs in the body ? What are the acids 
 
 found in the body ? What are the chief bases and salts found 
 in the body ? 
 
 46. 47. What is the difference between an organic and an inorganic 
 
 proximate constituent ? 
 
 47. Mention some of the chief nitrogenous bodies found in the tissues. 
 
 Where are gelatin, chondrin, and elastin found ? 
 
 48. What is a carbo-hydrate ? Give examples. What is the chemical 
 
 nature of a fat ? Why is a fat a better source of heat than a 
 carbo-hydrate ? 
 
 49. What is the chief nitrogenous waste matter found in the urine ? 
 
 Describe the chief physical "characters of urea. Show the 
 relation of urea to a proteid. 
 SOj 5') 5^1 S3j S4- Enumerate the chief, chemical processes 6ccurring 
 in the body. 
 
 51. What is an oxidation? What are the last products of the oxida- 
 
 tion (a) of proteids, and {Jb) of carbo-hydrates and fats ? 
 
 52. What do you mean by dehydration and dissociation ? 
 
 53. 54. What is understood by synthesis and reduction ? 
 
 55. Distinguish between zymolysis and fermentation. What does the 
 
 yeast plant do ? What is an enzyme ? Mention the chief 
 zymolytic processes occurring in the body. 
 
 56. What do you understand by the ' instability of organic compounds?' 
 
 What is the ' circulation of matter ?' 
 
6s 
 
 CHAPTER III. 
 THE BODY IN ACTION. 
 
 57. Introductory. — Having considered the structure 
 of the body, and the nature of the chemical changes 
 happening in it, we are now in a position to view its mode 
 of action as a whole. In the first place, we see that the 
 animal body moves apparently spontaneously. Animals 
 run, leap, walk, fly, swim; they move about from place 
 to place ; and they may move only one part of the body, 
 as when we open or close the mouth, or lift a pencil from 
 the table with the fingers. We soon observe, also, that 
 there are movements occurring in the body itself, often 
 rhythmic in their character (that is to say, they are repeated 
 over and over again), as the movements of the thorax in 
 breathing, and the beating of the heart, which we can feel 
 by placing the hand over the left side. Thus one of the 
 most remarkable characteristics of the living body is 
 movement. 
 
 58. Heat. — We next notice that the body of the higher 
 animals — and we take as an example the human body we 
 are specially studying — is warm. Suppose we place the 
 bulb of a thermometer in the armpit, and leave it there for 
 a few minutes, we shall find that in health it registers a 
 temperature of about 98-4 degrees on the Fahrenheit scale, 
 and a few observations made on a healthy person would 
 convince us that this temperature does not vary much (not 
 more than a fraction of a degree) during the twenty-four 
 hours. Still more remarkable, we would find that the 
 change of temperature is very slight at different seasons of 
 the year. During the heat of summer, or the cold of 
 winter, we would not find a greater change, up or down, 
 than a degree or a fraction of a degree. The body of man, 
 
66 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 therefore, is not only warm, but it maintains a uniform 
 temperature, although the temperature of the external air 
 may vary very much. Now, a hot body cools by giving oflf 
 heat to surrounding objects; and if the human body is 
 hotter than the surrounding air, it must constantly be 
 losing heat. But the temperature is uniform, as we have 
 seen; although the temperature of the surrounding air may 
 change. It follows, therefore, that a quantity of heat must 
 be produced in the body to make up for the quantity lost. 
 This shows us two things : (i) that the living body pro- 
 duces heat; and (2) that there are arrangements for main- 
 taining a uniform temperature — in other words, for balanc- 
 ing the income and the output of heat. 
 
 59. Food. — Further, we find that a living body requires 
 food. If an animal is starved, it becomes thinner and 
 thinner, the fat being used up in the first instance, and in 
 course of time all the tissues become wasted. During 
 starvation an animal feeds upon itself. In ordinary circum- 
 stances, however, this wasting is prevented by new supplies 
 of material introduced in the form of food. Along with 
 that which is usually called food, the process of breathing 
 introduces into the body large supplies of oxygen, and this 
 oxygen is as necessary as food for the well-being of the 
 body. No animal will live in an atmosphere where there 
 is no oxygen. Food and oxygen are thus introduced daily. 
 
 60. Waste of Matter. — Not only is new matter daily 
 introduced, but old matter is daily removed from the body. 
 This we may call waste matter. This waste matter is of 
 various kinds, and it is separated by various organs. 
 Thus we find the lungs separating water and carbonic 
 acid; the skin, water, carbonic acid, saline matters, and 
 certain organic substances, chiefly of a fatty nature ; the 
 LIVER, water, saline matters, some colouring matters, and 
 some organic substances ; and the kidneys, water, nitro- 
 genous substances, chiefly urea, saline matters, colouring 
 
THE BODY IN ACTION. 67 
 
 matters, and to a small extent carbonic acid. Certain matters 
 are also separated by the intestinal canal, and, chief 
 among these, the materials of food that have not been 
 digested or absorbed ; but although the latter have passed 
 through the intestinal canal, they have never really entered 
 into, or become part of, the body. If we examine these 
 waste substances carefully, we find they may be grouped 
 thus : water, saline matters, non-nitrogenous matters, and 
 nitrogenous matters. As most of the water and saline 
 matters are introduced in the food, they can scarcely be 
 classed as substances arising from the tear and wear of 
 the tissues. The chief non-nitrogenous waste substance 
 is carbonic acid, given off mainly by the lungs, and the 
 representative nitrogenous substance is urea. Both of 
 these substances may be regarded as waste products. 
 As we have seen, carbonic acid is composed of carbon 
 and oxygen, and the amount of carbonic acid given 
 off daily, chiefly by the lungs, is the measure of the 
 amount of carbon eliminated. Thus an adult doing a 
 moderate amount of work gives off by the lungs about 
 3600 grains of carbon ; to this we must add about 300 
 grains separated by the skin, and also the carbon in the 
 urea and other nitrogenous waste matters, amounting to 
 about 120 grains, or 3600 + 300-1- 120= 4020 ; or, say, 
 4000 grains. In a similar way, the amount of urea is the 
 measure of the quantity of nitrogen given off. An adult 
 man eliminates about 300 grains of nitrogen. The sub- 
 stances eliminated contain about 90 grains of hydrogen 
 and about 10,000 grains of oxygen. Add to this about 
 480 grains of saline matters, such as chlorides, sulphates, 
 and phosphates of soda, lime, magnesia, &c., separated by 
 the kidneys and bowels, and we find a total of nearly 
 15,000 grains, or about 2 pounds' weight, of matter elimin- 
 ated from the body daily. 
 
 61. Waste of Energy.- — When the body works, it 
 
68 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 expends energy. This it does chiefly in two ways : (i) as 
 heat, and (2) as mechanical work. We have already 
 considered heat. As regards mechanical work, the body 
 expends energy in moving about, as in locomotion, in lifting 
 weights, and, in short, in many ways of doing work, as in 
 the daily life of a labouring man. All this expenditure is 
 in doing what we may call outside work ; but the body, 
 considered as a machine, does inside work as well. Thus 
 work is done by the beating of the heart, and by the move- 
 ments of respiration. The body is thus always losing 
 energy, just as it is always losing matter. It is possible, 
 also, to measure this expenditure of energy, and to express 
 it in terms we can understand. The unit of energy usu- 
 ally employed is the foot-pound — that is, the amount of 
 energy required to lift one pound one foot high. Suppose 
 we take the case of a labouring man doing a fair amount 
 of hard work during eight hours. During 24 hours 
 the amount of work done by his heart may be stated at 
 361,500 foot-pounds; add to this the work done in the 
 movements of respiration, 84,591 foot-pounds; to this, 
 again, add the work actually done during eight hours of 
 labour, 903,750 foot-povmds; and, last of all, add the 
 energy represented by the amount of heat produced by 
 his body during 24 hours, 4,482,600 foot-pounds. The 
 total energy expended in 24 hours thus amounts to 
 nearly 5,000,000 foot-pounds. To make up for this daily 
 expenditure of energy by an adult man, fresh energy must 
 be introduced. This is accomplished by the food. Food 
 may be regarded as matter containing energy stored up in 
 it, or, as it is expressed, energy in the potential state, and 
 it is liberated by the body, appearing as motion and heat. 
 Now we can estimate the income and the output of matter 
 daily, and a balance can be struck, showing that, when the 
 body remains approximately at the same weight from day 
 to day, the amount of the income is that of the output. 
 
THE BODY IN ACTION. 69 
 
 III like manner, we can estimate the amount of energy 
 stored up in a given quantity of food. If we burn an 
 ounce of starch, we can measure the amount of heat pro- 
 duced, and from that calculate the amount of energy 
 represented. If this be done with the diet of a labouring 
 man, who expends in 24 hours the energy above indicated, 
 we find that it supplies all the energy required; that 
 is to say, we can strike a balance as regards income and 
 output of energy, just as we can strike a balance between 
 income and output of matter. 
 
 62. The Phenomena in a Muscle. — The facts stated 
 generally in the last few paragraphs will be better under- 
 stood if we consider shortly some of the phenomena that 
 happen in a living muscle. As we have seen, muscles, by 
 their power of contracting, are the organs by which the 
 movements of the body are effected. Each muscle has 
 its own proper work to do. Take, for example, the biceps 
 muscle in front of the upper arm, which, by its contraction, 
 bends or flexes the forearm on the arm at the elbow joint. If 
 we perform this movement repeatedly at short intervals, we 
 soon have a sense ol fatigue, which passes off if we stop 
 the movement and allow the muscle to rest for a sufficient 
 time. Dissection shows us that the muscle is suppHed 
 with nerves that can be traced to the spinal marrow, and 
 nerve fibres can be followed up to the brain. If these 
 nerves were divided, we could not voluntarily — that is to 
 say, by an effort of the will — cause the muscle to contract, 
 or, in other words, we could not bend the forearm on the 
 arm at the elbow joint. The nerves, then, are the agents 
 by which the muscle is caused to contract, and what is 
 termed a nervous impulse passes along the nerve fibres 
 from the brain to the muscle; there the impulse sets up some 
 changes in the muscle, and the result is a muscular con- 
 traction. Now, a muscular contraction is a movement ; in 
 other words, the muscle expends or liberates energy as 
 
7o ELEMENTARY HUMAN PHYSIOLOGY. 
 
 movement. Further, if we examine by proper methods the 
 muscle while it contracts, we find it becomes warm — that is 
 to say, the muscle liberates energy as heat. Energy can 
 only be set free when chemical changes occur in the muscle, 
 and when we look for such changes, there is not much 
 difficulty in finding evidence of their existence. Thus we 
 find that a muscle uses up oxygen and produces carbonic 
 acid. In addition to the production of carbonic acid, the 
 muscle becomes acid, from the formation of an acid called 
 sarcolactic acid, and numerous waste nitrogenous matters 
 are formed, such as kreatin, sarcosine, &c., bodies found 
 in the juice of meat, such as Liebig's extract. There is also 
 evidence that certain bodies are used up by the muscle. 
 Thus it requires oxygen. The muscle also uses a peculiar 
 carbo-hydrate formed in the liver called glycogen, and it 
 uses also various proteid substances. The chemical 
 phenomena happening in a muscle are essentially those of 
 oxidation — that is, the union of oxygen with the carbon of 
 the tissue of the muscle. The process is not so simple as 
 here stated. Carbon does not simply unite with oxygen. 
 Numerous intermediate bodies are formed in the process, 
 but the ultimate restilts are mainly the formation of car- 
 bonic acid and nitrogenous waste bodies. Thus we see 
 that in a muscle, when it works, energy is set free as motion 
 and heat, and waste bodies are formed. The muscle may be 
 taken as the type of other kinds of tissues. Heat is 
 probably always liberated, and chemical products are no 
 doubt always formed, but outward visible motion may not 
 be one of the phenomena. 
 
 63. The Blood. — Tissues, during their activity, being 
 thus the seat of active chemical changes, in which certain 
 substances are used up and others are formed, it is clear 
 that there must be some means by which these new 
 materials are brought to the tissues, and by which the 
 waste substances are removed. This is accomplished by 
 
THE BODY IN ACTION. 71 
 
 the blood, and by the circulation of that fluid in the tissue. 
 Every tissue is more or less supplied with blood-vessels, 
 and the blood circulating in minute thin-walled tubes, the 
 capillaries, is brought into close proximity to the elements 
 of the tissues. From these minute vessels a fluid passes 
 out, holding in solution materials required by the tissues 
 for their nourishment. This fluid, called lymph, bathes the 
 tissues, so that the elementary tissues, the cells and fibres, 
 live in a fluid. From this fluid they take up oxygen and 
 nutritive materials, such as proteids, fats, carbo-hydrates, 
 saline matters, and water, and thus the living elements are 
 built up. The constructive process is sometimes said to 
 be anabolic, a word meaning building up. Thus we may 
 speak of anabolic processes repairing a muscular fibre, 
 when it has been worn out and exhausted by the activity 
 called contraction. When a tissue has thus been built up, 
 we may suppose it to be fit for its special function, and 
 this function is discharged under the action of some kind 
 of stimulus. In the case of muscle, the normal stimulus 
 is the action of the nervous impulse already alluded to. 
 Chemical changes are thus set up in the muscle, and waste 
 products are formed. The process is now one of pulling 
 down, or, as it is called, katabolic, and it is associated 
 with the two phenomena happening in a muscle, the 
 liberation of energy as movement and heat ; in other words, 
 the muscle becomes warmer, and it contracts. Similarly, 
 all living tissues are repaired after exhaustion by the 
 materials brought to them by the blood ; they (the tissue 
 elements) perform their appointed function under the 
 action of a stimulus; and the performance of the 
 function involves tear and wear, or the formation of 
 waste matters. 
 
 64. Absorption of Waste Matters. — The waste 
 matters arising from the breaking down of tissues, as 
 one of the results of their vital activity, must be removed. 
 
72 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 If allowed to accumulate, they become injurious. Con- 
 sequently they are quickly absorbed and carried to various 
 organs, called the organs of excretion. The absorption of 
 waste matters is carried on by two sets of vessels or 
 minute tubes, found in great numbers, and usually forming 
 plexuses or networks with extremely fine meshes. The 
 vessels are (i) the capillaries, already mentioned, and 
 (2) another set of vessels termed lymphatics. Many waste 
 matters are no doubt at once absorbed by the capillaries, 
 and thus reach at once the blood-stream. The lymphatics 
 originate in fine channels or spaces among the elements of 
 the tissues, such as cells or fibres, and from these spaces 
 delicate vessels carry off the fluid called the lymph, which, 
 as already seen, in the first instance comes from the 
 blood. The lymph contains the excess of nutrient matter 
 that came from the blood to nourish the tissues. The 
 portion not used up by the tissues is now the lymph, and 
 to this is added various waste substances that have corae 
 from the breaking down of the tissues. The lymph, 
 however, is not thrown out as useless, but is carried, in the 
 first instance, to certain organs called lymphatic glands. 
 In these it is submitted to various alterations, and then it 
 is ultimately poured back into the blood by great tubes 
 joining the veins at the root of the neck. 
 
 65. Removal of Waste Matters or Excretion. — The 
 blood, thus contaminated with waste substances, either 
 directly by capillary absorption or indirectly by lymphatic 
 absorption, passes to various organs, by which those waste 
 matters are removed. In particular, the lungs carry off 
 the carbonic acid, the chief non-nitrogenous waste product, 
 and the kidneys remove urea, the chief nitrogenous 
 material. Certain matters are also eliminated by the skin, 
 liver, and bowels. Thus, by the function of excretion, the 
 blood is maintained in a state of normal purity, so far as 
 waste products are concerned. 
 
THE BODY IN ACTION. 73 
 
 66. Formation of Blood. — We have seen that 
 materials are constantly being removed from the blood 
 for the nourishment of the tissues. To make up for this 
 loss, new materials must be added to it, and these materials 
 are obtained from the food. The food, however, is usually 
 very unlike blood both physically and chemically, and it 
 cannot pass directly into the blood. The food is sub- 
 jected to certain physical and chemical processes in the 
 important function of digestion, a function carried out in 
 its various stages by many organs, constituting the organs 
 of digestion. Thus the food is broken down by the action 
 of the jaws and teeth, it is acted on by the saliva, and it 
 is swallowed and passed into the stomach. There it is 
 acted upon by the gastric juice, and by movement and 
 heat. It then passes into the intestines, and is submitted 
 to the influence of the intestinal juice, the bile, and the 
 pancreatic juice. The result of these actions is to break 
 up the food into a state of fine subdivision, and to render 
 it ultimately soluble. It is then absorbed, and thus reaches 
 the blood. The blood thus receives new supplies of 
 matter from the alimentary canal, it receives oxygen from 
 the air by the lungs, and, as already seen, it receives the 
 lymph. Finally, to the blood are added certain cells 
 from organs termed blood-glands. These always contain 
 a tissue, termed adenoid tissue, in which blood-corpuscles 
 are formed. This tissue abounds in - the spleen, in the 
 thymus gland, in the walls of the alimentary canal, in the 
 marrow of bone, and in lymphatic glands. Thus the 
 blood is hourly renovated and fitted for purposes of 
 nutrition, and it is driven through the body by the 
 mechanism of the circulation. 
 
 67. General Influence of Nervous System. — This 
 part of the body, which includes the brain, spinal cord, 
 nerves, and the organs of sense, is that by which we will, 
 think, feel, perform voluntary movements, and obtain our 
 
74 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 knowledge of the world outside our own -tody. It is a 
 system consisting of many organs, and it controls and 
 regulates all the other organs. As already pointed out, 
 nerves pass to the muscles, and it is by impulses trans- 
 mitted along these nerves that the muscles are caused to 
 contract. Such nerves are called motor nerves. Again, 
 when we prick the tip of the finger with a needle, we 
 irritate nerve fibres, and these carry an impulse to the 
 brain, giving rise to changes there which arouse a 
 sensation, or a consciousness of pain, which sensation we 
 refer to the tip of the finger, although it is due to changes 
 in the brain, far removed from the finger. Nerves that 
 carry impulses inwards so as to cause sensations are called 
 sensory nerves. There are thus two classes of nerves, of 
 which these may be taken as types. One class, as, for 
 example, the motor, carries impulses outwards from 
 central organs to the periphery or outer parts of the 
 body, and hence is often called efferent. The other class 
 carries impulses inwards from the periphery to the cen- 
 tral nervous organs, and hence is called afferent. Of 
 each class there are several varieties. Thus, of efferent 
 nerves we have (i) nerves ending in muscles, causing 
 motion, and hence called motor nerves ; (2) nerves ending 
 in glands, causing secretion, and hence called secretory 
 nerves; and (3) nerves connected with blood-vessels, 
 regulating their calibre, and hence termed vaso-motor 
 nerves. Of afferent nerves we have (i) nerves causing 
 sensations of touch, pressure, &c., referred chiefly to the 
 skin, and termed nei-ves of touch or general sensation; and 
 (2) nerves from the organs of special sense or special 
 sensation, such as (a) from the eye, causing vision ; (b) from 
 the ear, giving rise to sound ; if) from the nose, producing 
 sensations of smell ; and (d) nerves from the tongue, con- 
 nected with taste. There are also nerves from the skin, 
 which arouse sensations of heat and cold, and pain ; from 
 
THE BODY IN ACTION. 75 
 
 the muscles that give us information as to position and 
 state of contraction of the muscle (the muscular sense) ; 
 and from the internal organs, such as the lungs, heart, 
 stomach, &c., that occasionally carry impulses to the brain, 
 and give rise to various sensations, which we locate in or 
 near the organ from which the message comes. 
 
 68. Reflex Acts. — Nerves issue from and enter the 
 cord, and issue from and enter the base of the brain, 
 and, as we have seen, they carry afferent and efferent 
 messages. Sometimes these messages are connected with 
 sensation, but sometimes we may be quite unconscious 
 of anything having taken place. For example, we may, 
 by an effort of will, move the right arm or leg, and we 
 know that we have made the movement. These are 
 movements of which we are conscious. But we may see 
 exactly the same movement performed when a person is 
 quite unconscious, as in profound sleep, or in the state 
 called coma, seen in many diseases. The movement, in 
 these circumstances, is excited usually by an irritation of 
 a sensory nerve. We may cause the movement, for ex- 
 ample, in a sleeping person by touching the palm of the 
 hand or sole of the foot with a feather. The person has no 
 sensation ; he is quite unconscious ; he exercises no will- 
 power or volition ; and yet the movement is made. Such 
 an action, of which there are many varieties, involving {a) 
 an afferent impulse ; {b) a nerve centre in the cord or 
 brain ; and {c) an efferent impulse to the muscles involved is 
 known as a reflex action. There are many reflex centres 
 in the cord or brain, and they often act automatically in 
 carrying on or modifying functions necessary to life, such 
 as breathing, the state of the circulation in the vessels, and 
 the action of the heart. 
 
 69. The Brain and Cord. — The spinal cord is the 
 chief centre for reflex acts. It also contains great strands 
 of nerve fibres passing upwards to the brain and down- 
 
76 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 wards to lower parts of the cord. From the sides of the 
 cord issue the spinal nerves, afferent and efferent, as 
 already described. The brain is also connected with 
 reflex acts by means of great masses or ganglia near its 
 base, such as the medulla (or bull)), the pons, and the proper 
 ganglia of base, which, arranged in pairs from before back- 
 wards, are known as the corpora striata, optic thalami, 
 and corpora quadrigemina. Over all these we find the 
 cerebrum, which is concerned in sensation, volition, and 
 intellectual acts. It is especially the organ of the mind. 
 Lastly, the lesser brain or cerebellum has to do with the 
 co-ordination or regulation of movement — 'that is to say, it 
 regulates the amount of contraction of each muscle and 
 the order of contraction of the muscles in a group 
 associated for ' a particular movement Each organ of 
 the body is thus brought into relation with the central 
 nervous system by afferent nerves, while its operations are 
 more or less under the control of the central nervous 
 system by efferent nerves, and, finally, the central nervous 
 system is itself the seat of operations that are closely 
 associated with all that we understand by the mind. 
 
 70. The Maintenance of the Erect Posture. — 
 This will be discussed under Animal Mechanics. 
 
 71. Life. — It is impossible to define what life is. 
 Many attempts have been made, and probably the most 
 successful is that of Bdclard : ' Life is organisation in 
 action.' The word life suggests vitality, and physiologists 
 frequently speak of vital forces, or vital actions. By a 
 vital action is meant simply an action which we cannot 
 at present explain by any chemical or physical laws. 
 The time may come when some phenomena now con- 
 sidered vital may be so explained. These vital phe- 
 nomena, at present unexplained, may be thus enumerated : 
 (i) differentiation in growth, that tendency which an ovum 
 has, by hereditary peculiarities, to develop into a particular 
 
THE BODY IN ACTION. 77 
 
 kind of animal, or that tendency which causes the 
 apparently similar cells of the embryo to develop into 
 the various kinds of tissues ; (2) irritability and con- 
 tractility, properties of muscular fibre ; (3) excitability, a 
 property of nervous tissue ; lastly (4), mental acts, such 
 as sensation and volition. Now it must be pointed out 
 that we are acquainted with many of the physical con- 
 ditions of these phenomena, but not with all. When we 
 know all the physical conditions, then we shall probably 
 not speak of them as vital phenomena. Even at present 
 no scientific physiologist assumes the existence of a ' vital 
 force ' as distinct from other forces, but he contents him- 
 self by stating that there are various phenomena which, 
 in the present state of science, he cannot explain by 
 chemical or physical laws. 
 
 72. It may be noted, also, that in an individual we find 
 different manifestations of life. Thus we have the life of 
 each independent cell or fibre, the life of each organ, and, 
 lastly, the life of the whole individual, or somatic life. 
 
 73. Death. — Death is the cessation of all vital pheno- 
 mena, without the capability of resuscitation. During the 
 whole of the lifetime of an individual there is death in 
 one sense occurring here and there throughout the body. 
 Each tissue is developed, grows to maturity, performs its 
 functions, decays, and dies. Probably no tissue lasts 
 throughout the whole of the somatic life. Thus the cells 
 of the blood are continually changed. Again, hairs, nails, 
 feathers, and teeth have each a certain period of existence, 
 at the termination of which they die and separate from the 
 rest of the body. This may be called local death. At 
 last, however, a time comes when the general death of the 
 body takes place. This is what we usually term death. 
 It results from failure either of the action of the heart, of 
 the lungs, of the brain, or from death of the blood, as in 
 cases of severe septic poisoning. Death beginning at the 
 
78 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 heart {fainting) is termed syncope, at the brain, coma, and 
 at the kings, asphyxia. When the action of the heart 
 becomes weaker and weaker until it ceases to beat, either 
 from feebleness of its walls, or from poisoning by carbonic 
 acid, or from want of oxygen, in consequence of a state of 
 asphyxia, death is said to occur by asthenia. After somatic 
 death, the tissues may live for a short time, but they 
 gradually die one by one. Muscular irritability disappears, 
 and the muscle stiffens from coagulation of its substance. 
 This rigid state, the ' stiffness of death,' is called cadaveric 
 rigidity. After a time the rigidity passes off, the muscles 
 and other tissues become soft, and the body, subjected to 
 the influence of putrefactive organisms, and, finally, to 
 the physical and chemical agencies of nature, is resolved 
 into the elements of which it was at first composed. 
 
 Questions. 
 
 57. 58. What are the two most evident characteristics of living beings ? 
 
 58. Explain generally how the human body maintains an equable 
 
 temperature in a hot summer day and in a cold winter day. 
 
 59. Why must a living being be supplied with food ? 
 
 60. Enumerate the chief waste substances given off by a living being, 
 
 and mention the channels by which they are given off. How 
 much carbon and nitrogen are given off daily ? 
 
 61. Show how a human being expends energy. What is the distinc- 
 
 tion between the internal and the external work of the body ? 
 
 62. Describe the chief phenomena shown by a living contracting muscle. 
 
 63. What are the arrangements in the body by which the ' tear and 
 
 wear ' of the tissues is repaired ? What is meant by the terms 
 ' katabolie ' and ' anabolic?' 
 
 64. 65. How are waste matters absorbed and eliminated ? 
 
 66. Give a general account of the formation of the blood. 
 
 67. What is the distinction between a motor and a sensory nerve ? 
 
 68. Describe, and give an example of a reflex act. 
 
 69. State generally the functions allotted to the chief parts of the 
 
 central nervous system. 
 
 71. What are the chief phenomena of life ? 
 
 72, 73. What do you understand by death ? What is the distinction 
 
 between somatic and local death ? 
 
79 
 
 DIVISION II.— HISTOLOGY. 
 
 CHAPTER I. 
 
 THE STRUCTURE AND FUNCTIONS OF THE 
 ELEMENTARY TISSUES* . 
 
 The elements of the tissues, in which delicate physio- 
 logical processes occur, are of such small size that they can 
 only be studied successfully with the aid of a good micro- 
 scope, capable of magnifying from 20 to 350 diameters 
 hnear. They have been variously classified, but, for con- 
 venience of description, we will group them under four 
 heads — the molecular, the cellular, the fibrous, and the 
 tubular elements of the tissues. 
 
 MOLECULAR ELEMENTS. 
 
 74. General Description. — ^When we examine under 
 the microscope almost any of the fluids of the body, or a 
 portion of any tissue teased out with needles in water, 
 numerous particles are seen, varying in size from the 
 loo^oofl th to the xinnyth of an inch in diameter. These 
 are molecules. They consist of minute fragments of other 
 tissues. 
 
 75. Movements of Molecules. — There are five modes 
 of molecular movement : 
 
 (i) The irregular to-and-fro movements known as the 
 Brownian movements, observed whenever molecules, 
 whether dead or alive, are suspended in fluids. 
 
 * This part is treated in the mgst elementary manner in the present work. 
 
8o ELEMENTARY HUMAN PHYSIOLOGY. 
 
 (2) Movements of molecules in the interior of cells, 
 due to movements of living matter in the cells, called 
 protoplasm. These may be seen in the interior of various 
 vegetable cells (such as those of the Chara, Vallisneria, 
 and Tradescantia), but they may also be seen in various 
 animal cells, as, for example, in the salivary cell, with 
 the aid of a powerful lens. These movements are some- 
 times definite in direction (streaming movements), and 
 are accounted for so far by a circulation of the fluid in 
 which they float ; but in other cases, as in the salivary 
 cell, they appear quite irregular, and have more of the 
 character of Brownian movements (fig. 45, b). 
 
 (3) The to-and-fro and zigzag movements of small 
 living things, of the nature of fungi, known as Bacteria, 
 and seen in putrid fluids. These may be due to the 
 action of cilia (see p. 86). 
 
 (4) The movements, often in a definite direction, of the 
 molecules of the yolk of the egg after fecundation. 
 
 CELLULAR ELEMENTS. 
 
 76. General Description of a Cell. — A cell (fig. 40) 
 
 is a microscopically small body, 
 
 consisting of a soft substance 
 
 termed protoplasm, in which 
 
 there may be imbedded a body 
 
 called a nucleus, c, in which 
 
 there may be a still smaller 
 
 Fig. 40. -Two Cells of round or body, d, known as the nucleolus. 
 
 oval form : o, ■ , 
 
 „ , „ , ^ Sometimes the external bound- 
 
 a, border of the cell : *, cell body ; 
 
 c, c, nuclei with nucleoli, d, d. ary of the Cell may become a 
 hardened stratum, a, which is 
 then called the cell membrane or cell wall. A cell is more 
 than a molecule in a physiological sense ; it is the smallest 
 physiological apparatus, to a certain extent complete and 
 independent. It is also a generally received doctnne that 
 
ELEMENTARY STRUCTURE OF THE CHIEF TISSUES. 8 1 
 
 all tissues originate in cells. Not infrequently several 
 nuclei may be seen in the same cell or mass of protoplasm, 
 as in fig. 43, a, representing a cell or mass of protoplasm 
 from the marrow of bone. 
 
 77. Size of Cells. — They vary in size from the ^^Vxyth 
 (coloured blood-corpuscle) to the xrirth of an inch (the 
 ovum). 
 
 78. Form of Cells. — This is extremely variable. The 
 primary form is spherical or oval (fig. 40) ; but by com- 
 pression they may become flattened (fig. 41) ; long and 
 
 Fig. 42. 
 
 !, columnar epithelium : h^ fusiform connective tissue 
 cells : c, stellate cell from lymphatic gland ; rf, proto- 
 plasmic cells, with no cell wall. 
 
 Fig. 41.— Flattened 
 
 scaly epithelium 
 
 Cells from the 
 
 lining membrane 
 
 of the human 
 
 mouth, 
 compressed, as in fig. 42, a ; fusiform, b \ and irregular or 
 stellate, c. 
 
 79. Nature of Protoplasm. — This is a somewhat vis- 
 cid matter sometimes having albuminous or fatty granules 
 imbedded in it. It seems to be an unstable albuminous 
 matter, insoluble in water, and coagulating at a high or low 
 temperature, or at death. It manifests properties which we 
 term vital, because we cannot account for these properties 
 by any physical processes. It forms the chief part 
 of young cells, but old cells may be filled with other 
 matters, such as fat, pigment, or mineral substances. 
 At an early stage, a cell (physiologically speaking) may 
 consist of nothing more than a little mass of granular 
 
 F 
 
82 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 protoplasm, but it usually contains a nucleus (as in fig. 
 42, d). 
 
 80. Chemical Constitution of Cells. — The cell sub- 
 stance, as already stated, consists of a tough, viscid albu- 
 minous substance which coagulates at deatli, or on being 
 heated up to a certain point. This is about all we know 
 at present regarding the chemistry of protoplasm. In 
 many cells, protoplasm appears to be converted into other 
 substances, such as enzymes or ferments (as the pepsin 
 found in the cells of the glandular coat of the stomach), 
 glycogen, a kind of animal starch found in the cells of the 
 liver, and fats. The nucleus differs from the cell substance 
 in resisting the action of weak acetic acid, and in having 
 a remarkable affinity for most colouring matters ; and 
 according to some authorities, it seems to be modified 
 albuminous matter resembling the substance of elastic 
 tissue. The nucleolus, from its refractive properties, is 
 supposed to consist of fat. 
 
 81. The Phenomena of Vitality in Cells. — These 
 are: (i) absorption of matter; (2) transformation of the 
 same, either into protoplasm or some material formed by 
 the cell, such as fat; (3) excretion of certain materials 
 which are to be got rid of so far as the, cell is concerned ; 
 (4) growth, or increase in size and development of parts by 
 the imbibition of new matter ; (5) proliferation, or the 
 development of new cells from the old one ; and (6) in 
 many, the property of contractility. The latter property, 
 which is one of the most remarkable phenomena of cell 
 life, may be observed in the colourless cells of the 
 blood, and in the cells found in inflamed parts. On 
 carefully watching these cells, they are seen slowly to 
 change their form by throwing out and retracting portions 
 of their body. These movements, from their resemblance 
 to those performed by the little amoeba found in ditches, 
 &c., are ternied amceboid. It is a most interesting fact that 
 
ELEMENTARY STRUCTURE OF THE CHIEF TISSUES. 83 
 
 there are many amoeboid cells in the living body which 
 wander from the blood-vessels throughout the tissues. 
 During inflammation, colourless blood cells pass from the 
 blood through the walls of the vessels into the surrounding 
 tissues, as seen in fig. 44, and become the cells of ' matter ' 
 OT pus. This phenomenon, which depends on the property 
 of contractility in these minute cells, not only accounts for 
 
 Fig. 43. Fig. 44. — Blood-vesselin Mesen- 
 
 a, mass of nucleated protoplasm from tery of Frog during inflamma- 
 
 niarrow of Bone ; b, lymph-cells, from tion, showing migration of col- 
 inflamed eye, showing amoeboid pro- ourless cells of the blood : 
 cesses ; c, various forms of colourless 
 
 cells of the blood. "' '^^ passing through membranous 
 
 wall of vessel ; ^, cells which have 
 passed through ; £-, coloured cells in 
 stream of blood. 
 
 certain of the phenomena of inflammation, but also shows 
 how it is possible that small particles of infecting substances 
 may be taken up by amoeboid cells and carried by the 
 latter to distant localities in the body, to the danger or 
 injury of the system. These amoeboid cells also devour 
 the minute fungi {bacteria and bacilli) that cause certain 
 diseases. They have thus a protective function. 
 
 82. Conditions necessary for Cell Life. — These 
 are: (i) they must live in a nutritive fluid, from 
 which they can select the various substances necessary 
 to enable them to carry on their functions ; (2) they 
 require a temperature not below zero nor above 145° 
 
84 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 F. — a low temperature retarding, while a high tem- 
 perature favours, all growth ; (3) they require room for 
 expansion and an appropriate locality; and (4) the cell 
 itself must be in a healthy condition — that is, the cell wall 
 must not become thickened unduly by mineral matter ; 
 the cell substance, or protoplasm, must not be unduly 
 loaded with albuminous, fatty, or mineral substances ; and 
 the nucleus in many cases must exist. 
 
 83. Reproduction of Cells. — Cells may multiply in 
 three ways: (i) by budding, a minute bud may grow 
 from the cell, and this finally drops off and becomes an 
 independent organism ; (2) by simple direct division of the 
 nucleus, followed by division of the whole cell (sometimes 
 called karyostenosis) ; and by indirect division, or karyo- 
 kinesis, in which division of the nucleus is preceded by a 
 number of remarkable forms appearing in it, due to move- 
 ments of the colourable matter {chromatin) existing in the 
 nucleus. 
 
 84. Varieties OF Cells. — Cells may be divided into: 
 (i) normal isolated cells, floating in a fluid, such as lymph, 
 chyle, and blood-corpuscles ; ,(2) cells with a small amount 
 of intercellular matter, such as epithelial cells ; (3) cells 
 embedded in, and intimately connected with, other tissues, 
 such as fat cells, pigment cells, and nerve cells ; (4) cells 
 on free membranes which secrete various fluids^secreting 
 or gland cells ; (5) cells which, during different periods 
 in the earlier stages of their development, present all the 
 characters and functions of cells, but the tendency ' of 
 which is to be transformed, or so arranged as to constitute 
 a tissue — -cells of transition — such as cartilage, colloid, con- 
 nective tissue, and embryonic cells ; aiid (6) cells found 
 only in morbid conditions of the tissue, such as pus cells, 
 cancer cells, and tubercle corpuscles. 
 
ELEMENTARY STRUCTURE OF THE CHtEF TISSUES. 85 
 
 Epithelium and Endotbelium. 
 85. General Description of Epithelium. — This is a 
 tissue (composed of cells in layers of greater or less thick- 
 ness) which (i) covers the external and internal surfaces of 
 the body, (2) lines the canals of exit, and (3) clothes 
 numerous closed cavities, such as that between the wall of 
 the chest and the lungs,' termed the pleura. The cells 
 found on free surfaces and in ducts are called epithelial 
 cells, while those which line the shut cavities have been 
 termed endothelial cells. There are different varieties of 
 epithelial cells, such as (i) flat, tesselated, or pavement 
 epithelial cells, from the lining membrane of the mouth (fig. 
 45, a) ; (2) globular or secreting cells from the ultimate 
 
 Fig. 45. 
 
 Drop of Saliva, showing : 
 
 '.^ pavement or squamous epithelium 
 
 from mouth ; and 3, salivary cells. 
 
 Fig. 46. — Simple coating ol 
 Columnar Epitlielium on a 
 Mucous Membrane : 
 
 a, cells ; 3, intercellular matter ; c^ d^ sub- 
 cellular tissue. 
 
 Structure of a gland (fig. 33) ; (3) columnar cells when 
 they adhere by their sides, as found on the mucous lining 
 of the intestinal canal (fig. 46); and (4) ciliated cells, 
 which may be either globular or columnar in shape, and 
 are distinguished by having small processes or cilia at 
 their free border (figs. 47 and 48). The function of 
 epithelium is partly protective and partly for secreting 
 certain matters from the blood. 
 
 86. General Description of Endothelium. — ^Lining 
 the interior of the closed cavities of the body, such as the 
 chest and abdomen, we find a thin membrane usually 
 
86 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 called a serous membrane. This membrane consists 
 essentially of a single layer of irregularly polygonal 
 nucleated cells (resting on a thin structureless membrane 
 
 Fig. 47.— Ciliated Epithel- Fig. 48.— Row of Ciliated Epithelium 
 ial Cells from the finer Cells from the trachea of a man : 
 bronchial tubes. a^ fibrous tissue ; b, basement membrane ; c, 
 
 df cells in various stages of development ; 
 e^ fully formed ciliated cells. 
 
 called a basement membrane) placed edge to edge (fig. 49, 
 a), known as endothelial c€ih. The cavities of the heart and 
 the whole of the blood-vessels are also lined by fusiform 
 cells (fig. 49, b, c) of a similar kind. 
 Serous membranes secrete a thin watery 
 fluid, called serum or serosity, which 
 lubricates the surface, and permits move- 
 ment of adjacent parts on each other 
 with little friction. 
 
 87. Ciliary Action. — Ciliated epi- 
 thelium is found in the air passages, 
 such as the nose, pharynx or throat, 
 brane' of'T^bTood- trachea or windpipe, and bronchial tubes, 
 vessel; b, similar in the cavities of the brain and central 
 ce s ISO ate . canal of the spinal marrow, in the middle 
 
 ear, in the uterus, and in a few other localities. Each 
 cell bears several cilia (figs. 47 and 48), and has a 
 nucleus. The beautiful undulating movement of cilia, 
 
 Fig. 49.— Endo 
 thelial Cells : 
 /t, from the pleura 
 
ELEMENTARY STRUCTURE OF THE CHIEF TISSUES. 87 
 
 sometimes similar to the appearance of a series of waves 
 travelling along the surface of a field of wheat, at other 
 times such as to convey the idea of running water, can 
 scarcely be described ; but it may be readily studied on 
 the gills of the common mussel, or on the tentacles of 
 many small sea-anemones, or other polypes. Ciliary 
 motion persists for some time after the death of the 
 animal, and in the case of cold-blooded aninjals it may 
 continue for eyen ten or fifteen days after decapitation. 
 The cause of ciliary movement is unknown. It does not 
 depend directly on the nervous system, nor on a supply of 
 blood, as it will continue in isolated parts for some time 
 after these influences have been removed. An ample 
 supply of oxygen is necessary for ciliary movement. The 
 action of cilia is undoubtedly to excite currents in the 
 fluids in which they are immersed. In many infusoria, 
 locomotion is entirely effected by the action of cilia. 
 In the human body, they assist in the onward movement 
 of mucus. Thtis, in the air passages, the action propels 
 mucus upwards towards the opening of the windpipe. 
 
 Pigment. 
 
 88. General Description. — This is found in the 
 
 deeper layer of the epidermis, or superficial layer of the 
 
 skin, and also in the choroid or pigmentary coat of the eye 
 
 (see Eve). It consists of cells 
 
 filled with coloured matter a ( 
 
 placed side by side. There 
 
 are two distinct forms of these 
 
 cells : (i) the polygonal (fig. 50, 
 
 ff), and (2) the irregular or stel- 
 
 J\ ^' . , ^„, , Fig. 50.— Pigment Cells : 
 
 late, as seen va b. The colours , ^ ., ,, ,. ,, 
 
 . rt, from choroid ; ^, from skin of frog. 
 
 of the various races of mankind 
 
 depend on a greater or less amount of pigment in the skin. 
 
 Such pigment cells are present in the skin of even the 
 
88 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 white races, and they are also found in the investing mem- 
 brane of the spinal cord, in the membranous part of the 
 internal ear, and in the interior of the nose. In the eye, 
 the pigment absorbs the redundant light j but its uses 
 in the skin and in other parts are unknown. Individuals 
 in whom pigment is wanting are called Albinos. 
 
 Pat. 
 
 89. General Description. — This tissue consists of 
 cells, termed fat cells, embedded amongst fine fibres. Tlie 
 cells are round or oval (fig. 51, «, b), from the -g^ih. to 
 the ^5Tyth of an inch in diameter, and each consists of 
 a delicate wall or envelope inclosing a drop of oily 
 matter. When young, they contain a nucleus, but this 
 disappears, or is pressed to the side of the cell (fig. 52, c). 
 
 Frequently small stel- 
 late groups of crystals of 
 fatty acids may be seen 
 in the interior (fig. 51, 
 b). Fattymatter is called 
 
 p.- g2 Fat ''''^^po^^ tissue. It forms a 
 
 Cell (highly considerable layer under- 
 magnified) : neath the skin ; covers 
 Fig. 51.— Fat Cells: o, fat globule; b, various internal organs, 
 
 membranous en- . . ... 
 
 veiopejr, nucleus f"ch as the kidneys J 
 ofceii;<i;, connec- is collected in the folds 
 
 tive tissue. ,. . . . 
 
 01 the serous membranes 
 of the abdominal cavity, 
 termed the mesentery and omentum; is common in the 
 neighbourhood of joints, outside the synovial membrane; 
 and it exists in large quantity in the bones, forming the 
 chief part of the marrow. It is richly supplied with 
 blood-vessels. The uses of fat are : (i) it acts mechani- 
 cally as a light, soft, elastic packing for the cavities of 
 the body, facihtating motion and diffusing pressure equally ; 
 
 e, imbedded amongst 
 fine fibres ; ^, isolated, 
 and containing small 
 stellate deposits of 
 crystals. 
 
ELEMENTARY STRUCTURE OF THE CHIEF TISSUES. 89 
 
 (2) being a bad conductor of heat, it retains the warmth 
 of the body — hence we find a thick layer of fat {blubber) 
 underneath the skins of animals Uving in arctic regions ; 
 and (3) being composed chemically chiefly of carbon and 
 hydrogen, it is oxidised in the tissues, and thus assists 
 in maintaining animal heat. In a well-nourished human 
 being, the amount of fat is said to be about -J^th of the 
 weight of the body, but no doubt it fluctuates. Repose 
 of body and mind, much sleep, and rich food favour the 
 development of fat, and in some cases, especially in 
 advanced life, the amount becomes so great as to con- 
 stitute what we term obesity, which cannot be regarded 
 as a healthy condition. 
 
 FIBROUS ELEMENTS. 
 
 90. A fibre is a solid elongated filament, microscopical 
 in size, and a number of these together constitute 2^ fibrous 
 tissue, of which there are four varieties found in the human 
 body. These are : (i) white fibrous tissue ; (2) yellow 
 elastic tissue ; (3) involuntary or non-striated muscular 
 fibre ; and (4) voluntary or striated muscular fibre. 
 
 White Fibrous Tissue. 
 
 91. General Description. — This is frequently called 
 connective tissue, because it binds the various tissues and 
 organs together. It is found underneath and in the skin, 
 between the muscles, in the blood-vessels, and other deep- 
 seated parts, forming sheaths for these structures, and it 
 enters more or less into the constitution of almost every 
 organ. It is also continuous throughout the body. Hence 
 dropsical effusions find their way throughout every part, 
 and suppurations may spread from the spot where the 
 ' matter' or pus was first formed. White fibrous tissue con- 
 sists of fine filaments (fig. 53, «) running in bundles which 
 
9° 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 often cross each other so as to form spaces or areolae. 
 Hence, where those spaces are large, it is termed areolar 
 tissue. In the meshwork lie fat cells, blood-vessels, &c. 
 In this tissue we also meet with small irregularly formed 
 nucleated cells (fig. 53, /, and fig. 54, a, b, c, d) called 
 
 ® 
 
 Fig. 53. Fig. 54. 
 
 a, connective tissue iii tendon ; ^, connective tissue from a, h, c, d, various forms 
 underneath the skin, showing a connective tissue of connective tissue 
 corpuscle; c, isolated white fibres; <^, yellow elastic corpuscles, 
 tissue ; e^ reticulated tissue of elastic fibres ; ^ con- 
 nective tissue corpuscles, connected by a fine filament. 
 
 connective tissue corpuscles. This kind of tissue swells up, 
 and becomes transparent and gelatinous on the addition of 
 a drop of weak acetic acid. Tendon or sinew is formed of 
 parallel bundles of white fibrous tissue (see fig. 53, a). 
 
 Yellow Elastic Tissue. 
 92. General Description. — This is found in the liga- 
 ments which join the arches of adjacent vertebrae, in the 
 coats of the larger blood-vessels, in the skin, and in many 
 other structures. It may be conveniently studied in a bit 
 of the ligamentum nucha, a ligament in the back of the 
 neek of a large quadruped for sustaining its heavy head. 
 It consists of strong, coarse, yellow, elastic fibres (fig. 53, 
 d, e), which show a tendency to split and to curl up at 
 the extremities. It is not affected by acetic acid. Its 
 chief property is elasticity. 
 
ELEMENTARV STRUCTltRE Of THE CHIEF TISSUES, gt 
 
 Muscular Tissue. 
 
 93. The two varieties of fibrous tissue above described 
 act chiefly in a mechanical way in supporting or binding 
 together, or in giving elasticity to various parts. Muscular 
 tissue, in addition, possesses the property of contracting 
 on the application of a stimulus. Of contractile fibrous 
 tissue there are two varieties. 
 
 (i) Involuntary or Non-striated Muscle. 
 
 94. General Description. — This is so termed because 
 its action is not subject to the will — that 
 is, we cannot cause contraction in a part 
 formed of it by willing to do so — and be- 
 cause it does not present the striated 
 appearance characteristic of the other 
 variety. It is found between the coats 
 of the membranous viscera, such as the 
 stomach, intestines, and bladder, in the 
 walls of the air-tubes, ducts of glands, &c. 
 It consists of flattened or ribbon-shaped 
 bands (fig. 55, a), which are composed of 
 fusiform or spindle-shaped cells, b, some- 
 times showing, on the addition of acetic 
 
 acid, an elongated nucleus. It contracts slowly when 
 stimulated. 
 
 (2) Voluntary or Striated Muscle. 
 
 95. General Description. — On examining one of the 
 muscles of the extremities 
 of any animal with the 
 naked eye, we observe 
 that it presents a fibrous 
 appearance. The bundles 
 are called fasciculi (fig. 
 56), inclosed in sheaths 
 
 Fig. 55. 
 
 a,portion of a band of 
 involuntary mus- 
 cular fibre ; b, iso- 
 lated cell, showing 
 nucleus. 
 
 Fig. 56. — Muscular Fasciculus show- 
 ing its division into fibres. 
 
92 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 of white fibrous tissue. A fasciculus consists of a number 
 of fibres, of varying size, each of which is inclosed in a 
 structureless sheath or membrane called the sarcolemma 
 (fig. 57). A fibre usually shows a tendency to cleave or 
 
 Fig. 57. — Muscular Fibre torn across, Fig. 58. — Muscular Fibre 
 and showing the delicate sarco- cleaving at the ends trans- 
 lemma between. versely into discs. 
 
 split up in two directions, transversely into discs (fig. 58), 
 and longitudinally into still smaller fibres, called fibrillx 
 (fig. 60). Each fibre shows transverse markings or stria 
 (hence the name), as seen in the various figures. This 
 
 Fig. 59. 
 Portion of Muscular Fibre : 
 Ej showing, its connection with the 
 tendon, b. 
 
 Fig. 60. — Portions of Muscular 
 Fibre highly magnified, showing 
 sarcous elements : 
 
 a. Urge fibril ; b, ultimate fibril ; f, small 
 fibre. 
 
 striation is due to the fact that the ultimate fibril (fig. 
 60, b) is composed of small square-shaped bodies or 
 discs placed end to end, some of which, from the manner 
 in which they are affected by light, appear dark, and 
 others light. The dark discs (which alone are contractile) 
 are termed the sarcous elements of Bowman. By studying 
 the figures, the cause of the striated appearance will be 
 understood. In the middle of the clear disc there is a 
 
ELEMENTARY STRUCTURE OF THE CHIEF TISSUES. 93 
 
 thin dark line {Debits line). The length of the fibres is 
 usually about three-quarters of an inch. The fibres at 
 each end of a muscle are attached by white ( v 
 fibrous tissue to the fibrous covering of bone [ ^ / 
 (fig. 59). Tht muscle of the heart shows s\\ort | W ' 
 square-shaped fibres, faintly striated, and con- ^""'^ 
 taining a nucleus (fig. 61). *i# I r-" . 
 
 96. Chemical Constituents OF Muscle. — ' j i 
 A living muscle in a state of repose contains, "" ) 
 within the sarcolemma of each fibre, a semi- ^^ 
 
 fluid substance called muscle-plasma, having Fig. 61. 
 an alkaline reaction. When this plasma is Muscular Fi- 
 squeezed out of jnuscle, it separates into two ^^ ^''°^ *^ 
 portions — a fluid termed muscle serum, and a 
 solid clot which consists of an albuminous substance 
 called myosin. The serum contains albuminous matters ; 
 glycogen, a kind of animal starch ; nitrogenous matters 
 formed from the decomposition of the muscle during action; 
 salts, chiefly of potassium ; water ; and gases, chiefly car- 
 bonic acid. When a muscle dies, the semi-fluid matter 
 solidifies, and the muscle stiffens. This is called rigor 
 mortis. After a muscle has been frequently stimulated to 
 contract, or has been kept for some time in a state of 
 contraction, the plasma becomes acid instead of alkaline, 
 from the formation of acid products of decomposition, 
 chiefly an acid similar to that formed in the souring of 
 milk, and termed sarcolactic acid. 
 
 97. Stimulation of Muscle. — When a muscle is stimu- 
 lated it contracts. This property of contracting on the 
 application of a stimulus is called irritability, a property 
 which has been shown to depend on the inherent structure 
 of the muscle itself, and not upon the nervous system, as 
 was at one time supposed. The stimuli capable of causing 
 a muscle to contract are : (i) the normal nervous stimulus, 
 transmitted along a nerve from a nervous centre ; (2) elec- 
 
94 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 trical stimuli, as when it is irritated directly by an inter- 
 rupted galvanic current, or by a Faradic current ; (3) chemical 
 stimuli,, such as the application of a strong solution of 
 common salt ; (4) thermal stimuli, such as the momentary 
 application of a hot wire ; and (5) mechanical stimuli, such 
 as prickings pinching, &c. 
 
 98. Work done by a Muscle. — When a muscle con- 
 tracts in its normal position, it does a certain amount of 
 work, in the form of mechanical movement. 
 
 As work cannot be done without expenditure of material, the 
 chemical composition of the muscle alters, so that the constit- 
 uents which are soluble in water decrease in amount, while 
 those soluble in alcohol increase. This fact clearly indicates 
 that chan_ges take place. When a muscle is stimulated, either 
 directly, or indirectly by stimulating the nerve, it does not 
 contract instantly, but there is a short period of inactivity, 
 followed by the contraction. This period, called the period 
 of latent stimzilation, has been found to amount to about the 
 liJisth part of a second. When a muscle contracts on stimula- 
 tion, it may do an amount of work, say, in lifting a weight, far 
 in excess of the energy represented by the stimulus. It thus 
 appears that the muscle may be regarded as containing energy 
 stored up, or in a potential state ; while the function of the 
 normal nerve stimulus is to set free this energy, or to make 
 it actual or kinetic. 
 
 99. Various states of Muscular Contraction.— When 
 a muscle receives a single shock or stimulus of sufficient 
 strength, say, from a galvanic battery, it makes one contraction. 
 If it receives a series of shocks, with sufficient time intervening 
 between the shocks, it contracts and returns to its former size 
 with each shock ; but each shock, after a certain time, weakens 
 the muscle, so that it by-and-by will not contract on the 
 application of the stimulus. This state of exhaustion of the 
 muscle is called muscular fatigue. If a muscle receives a 
 number of shocks in quick succession, so rapid that it has no 
 time to relax completely between the shocks, it becomes stiff 
 and rigid. The rigid condition thus produced is called Tetanus. 
 The contraction of a muscle in the living body is also an 
 
ELEMENTARY STRUCTURE OF THE CHIEF TISSUES. 95 
 
 effect of this kind. When a muscle, say, the biceps in the 
 front of the arm, contracts in obedience to a voluntary effort, 
 it does not do so by one nervous impulse being transmitted to 
 it along the nerve from the brain, but by the action of many. 
 One nervous impulse after another follows with great rapidity, 
 and in consequence the muscle gathers itself up and contracts, 
 as in tetanus. 
 
 100. Thermic Phenomena of Muscle. — Muscles are 
 hotter during contraction than during a state of rest. This 
 has been ascertained experimentally, and tlie heat thus pro- 
 duced may be regarded not only as an expression of the 
 chemical changes occurring in the muscle, but also as the 
 appearance, in the form of heat, of a portion of the energy 
 stored up in the muscle. 
 
 TUBULAR ELEMENTS. 
 
 10 1. A tube is composed of a wall and contents. In 
 the body we find four varieties of tubes, which will be 
 described in their proper place in discussing the functions 
 with which they are connected. They are (i) air-tubes, 
 in the air-passages and lungs; (2) blood-tubes, in the 
 various kinds of blood-vessels ; (3) dental tubules, forming 
 part of the structure of a tooth ; and (4) nerve-tubes, 
 usually termed nerve-fibres, the conducting filaments of the 
 nervous system. 
 
 There are certain tissues which cannot be conveniently 
 classified under any of the four divisions of molecular, 
 cellular, fibrous, and tubular elements. These are (i) 
 cartilage, or gristle ; and (2) bone. Of these we shall now 
 give a brief account. 
 
 Cartilage. 
 
 102. General Description. — When in mass, carti- 
 lage is opaque, pearly or bluish white, but translucent 
 when cut in thin slices. It is highly and perfectly elastic. 
 
96 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 There are two varieties, temporary and permanent. 
 Temporary cartilage is seen in the embryo, where the 
 skeleton is cartilaginous, but in due time the cartilage is 
 replaced by bone. Permanent cartilage continues as car- 
 tilage throughout life. It is seen covering the ends of 
 bones, and entering into the formation of joints, forming 
 an elastic pad which breaks the force of concussions ; 
 it forms the cartilages of the ribs (fig. 12), part of the 
 external ear, the nose, the eyelids, the larynx, the wind- 
 pipe, and the tube leading from the back of the throat 
 to the middle ear, known as the Eustachian tube. When 
 a thin piece of cartilage is examined microscopically, it 
 is seen to consist of a mass of finely granular material 
 known as matrix, in which lie imbedded nucleated cells, 
 the cartilage cells. When cartilage is boiled for a consider- 
 able time, it yields a substance termed chondrin. 
 
 103. Varieties of Cartilage. — These are : (i) hyaline, 
 
 in which the matrix is 
 clear and transparent, or 
 finely molecular, giving 
 it the appearance of 
 ground-glass (fig. 62, a) ; 
 (2) white fibro-cartilage, 
 in which the matrix has 
 Fig. 62.-Cartilage : become fibrous, the fibres 
 
 a, hyaline, showing cells lying in a slightly , . , , . ^ 
 
 granular matrix; *, yellow fibrous, showing havmg the Characters Ol 
 cells lying in meshwork of coarse fibres. thoSC of whitC fibrOUS 
 
 tissue, as seen in the discs between the vertebrae ; and 
 (3) yellow fibro-cartilage, in which the fibres resemble those 
 of yellow fibrous tissue, resisting the action of acetic acid, 
 and forming a dense matting or felt, in the meshes of 
 which the cells lie (fig. 62, b). Yellow fibro-cartilage is 
 sparingly distributed in the body, being found only in 
 certain of the cartilages of the ear and of the larynx. 
 
ELEMENTARY STRUCTURE OF THE CHIEF TISSUES. 97 
 
 Bone. 
 
 104. General Description. — Bones are divided by 
 anatomists into the long or cylindrical, the flat or tabular, 
 and the short or irregular. The femur is an example of . 
 the first (fig. 19), the parietal of the second, (fig. 10), 
 and the astragalus of the third (fig. 21). When any of 
 these bones is sawn across, two kinds of bony tissue 
 are seen — a hard compact part next the surfaces of the 
 bone, and a spongy or cancellated part formed of bands 
 and plates in the centre. In the centre of a long bone 
 
 Fig. 63.— Bone : 
 A, longitudinal section, showing ramifications of Haversian canals, a, c, d, e, andy^^ 
 lacunae and canaliculi. B, transverse section, showing one complete Haversian 
 system, a; part of another, b; and an outer lamina, e, e; a is the transverse 
 section of a Haversian canal. C, bone corpuscle in lacuna, highly magnified ; b, 
 bone corpuscle, a mass of protoplasm ; a, space between it and bony matter. 
 
 there is a canal termed the medullary canal, filled with 
 a soft, reddish, pulpy substance called the marrow. The 
 marrow, when examined microscopically, shows fat cells, 
 large nucleated cells (fig. 43, a) and blood-corpuscles. In 
 the cancellated tissue, both in the heads of the long bones 
 and in the flat and irregular bones, there is a pulpy matter 
 of a similar character. To examine the microscopic structure 
 of a piece of hard bone, two methods may be followed : 
 
 G 
 
gS KLEMENTARY HUMAN PHYSIOLOGY. 
 
 (i) by sawing oif thin sections of dried bonej polishing and 
 grinding them into extremely thin slabs on a lapidary's 
 wheel, or on a hone ; or (2) by steeping the bone in 
 dilute hydrochloric acid for a few weeks, so as to dissolve 
 out the earthy matter, and leave only the cartilaginous 
 basis, which is so soft as to be readily cut into thin sections 
 with a sharp knife. On examining a longitudinal section of 
 bone made by the first method, a series of canals are seen 
 ramifying through the bone (fig. 63, A), called Haversian 
 canals, for carrying blood-vessels, &c., and by the side of 
 these canals numerous little dark oblong bodies, from 
 which delicate dark lines pass. On examining a transverse 
 section of bone (fig. 63, B), a transverse section of the 
 Haversian canal or canals is seen, a, b, surrounded by 
 laminae of bone, in which are imbedded oval dark bodies 
 termed lacuna, from which radiate outwards and inwards 
 numerous very delicate canals known as canaliculi. In 
 dead bone, the lacunae and canaliculi are empty, or filled 
 with bone-dust, but during life each lacuna is occupied 
 by a little mass of protoplasm called a bone corpuscle 
 (fig. 63, C), and in the canaliculi fine filaments of proto- 
 plasm may be found. These arrangements are evidently 
 intended for the nutrition of the bone. The nutritious 
 matter transudes from the blood-vessels in the Haversian 
 canals, passes through the system of canaliculi, which 
 communicate with these to the first row of lacunae, and 
 so on throughout not only the entire Haversian system, 
 as it is termed, which surrounds the canal, a, but through 
 adjacent systems, such as b. 
 
 105. Growth of a Bone. — Every bone is formed either in 
 membrane or cartilage, and the process is called ossification. 
 It is a process too obscure and difficult to be treated of in this 
 elementary work, but there are certain practical facts regarding 
 the growth of a bone which may be briefly described. In the 
 early embryonic state, a long bone, say, the femur, is entirely 
 
ELEMENTARY STRUCTURE OF THE CHIEF TISSUES. 99 
 
 cartilaginous ; but at a certain definite period a deposit of 
 earthy matter takes place in the shaft, which gradually extends 
 towards each extremity, so that, about the eighth month of 
 fostal life, the shaft is 
 completely ossified, A, 
 but both ends are car- 
 tilaginous. At birth, 
 a second deposit of 
 earthy matter (termed 
 an ossific centre) has 
 taken place in the 
 lower end, B. After 
 birth, the bone grows 
 in length and thick- 
 ness. At the age of 
 one year, a second os- 
 sific centre makes its 
 appearance in the head 
 of the bone, C. We 
 have now three ossi- 
 fied portions, the shaft, 
 the lower extremity, 
 and the upper extrem- 
 ity. Between the ossi- 
 
 Fig. 64. — Ossification of the Femur : 
 
 A, femur of a fcetus about eight months ; the shaft 
 is osseous ; both ends are cartilaginous. 6, f^iur 
 of a child at birth, showing a nucleus of earthy 
 matter, 2, in the lower end. C, femur of a child 
 of about a year old, showing a nucleus in the 
 articular head, 3. D, femur of the fifth or sixth 
 year, where ossification has extended from the 
 shaft into the nucleus in the head, and a nucleus 
 has appeared in the great trochanter, 4. E, 
 femur about the age of puberty, showing more 
 complete ossification, and a nucleus in lesser 
 trochanter, 3. 
 
 fied shaft and the par- 
 tially ossified extremities, the bone is still cartilaginous, and 
 it is here that growth in length chiefly takes place. A study 
 of fig. 64 will show the subsequent steps by which the bone 
 becomes entirely ossified. The ossified portions separate from 
 the shaft are termed epiphyses. After a bone has become 
 completely ossified, it ceases to grow in length, but it may 
 increase in thickness by the development of new bony material 
 on the outside, beneath the fibrous covering of the bone termed 
 the periosteum. Each bone is richly supplied with blood by 
 the vessels of the periosteum, and by a special nutrient vessel 
 which usually penetrates the bone. These facts show (i) that 
 bone is not a dead inert mass, as many may. suppose, but that 
 it is a living, growing tissue, especially in early life ; and (2) 
 that in early life, before the long bones of the lower extremities 
 
lOO ELEMENTARY HUMAN PHYSIOLOGY. 
 
 have completely ossified by union of the epiphyses with the 
 shaft, there is danger of bending the bones at the cartilaginous 
 portions and in the shaft by allowing the child to walk at too 
 early a period. 
 
 io6. Chemical Constitution of Bone. — Bone consists 
 of an earthy and of an animal part. The animal part is a soft 
 flexible substance, obtained, as above mentioned, by steeping a 
 bone in diluted hydrochloric acid. On boiling this, it yields 
 gelatin. The earthy part, got by burning bones, consists 
 largely of tribasic phosphate of lime, carbonate of lime, fluoride 
 of calcium, phosphate of magnesia, and chloride of sodium. In 
 old age, the bones become brittle, from the large amount of 
 earthy salts they then contain. 
 
 Questions. 
 
 75. Describe the different kinds of molecular movements. 
 7^. Draw the form of a cell, and describe its various parts. 
 79. What is protoplasm ? 
 
 81. How may we know that a cell is alive ? 
 
 82. What conditions are favourable to cell growth ? 
 
 83. What are the various ways in which cells multiply ? 
 85. Enumerate the different kinds of epithelium. 
 
 87. Describe ciliary motion. Where are cilia found in the body? 
 
 88. Where are pigment cells found ? 
 
 89. Describe the structure and uses of fat. 
 
 91. Describe white fibrous tissue. Where is it found ? 
 
 94. Where do you find non-striated muscular fibre ? 
 
 95. Describe the structure of striated muscle. 
 
 96. What do you know of the chemical composition of muscle ? 
 
 97. How may a muscle be called into action ? 
 
 99. What is cramp or tetanus ? What conditions fatigue a muscle ? 
 102. Describe the varieties of cartilage found in the body. 
 
 104. Describe the structure of bone. 
 
 105. How does a bone grow in length and in thickness ? 
 
 106. How could you obtain the organic part of a bone ? How could 
 
 you obtain the ash ? What is the composition of the ash ? 
 
DIVISION III.^SPECIAL PHYSIOLOGY. 
 
 CHAPTER I. 
 THE BLOOD. 
 
 107. General Characters. — The blood is the most 
 important and most abundant fluid in the body. With 
 the exception of a few tissues, such as the centre of the 
 cornea of the eye, the nails, and the hair, it pervades every 
 part of the body, as may be shown in the case of the skin 
 by puncturing any part of it with a needle. The total 
 quantity is estimated at about one-eighth of the weight of 
 the body, or about 20 pounds in a man of average size. 
 Its colour is red, but it varies from a bright scarlet in the 
 arteries to a dark purple in the veins. When, however, a 
 minute drop is examined under the microscope, it is seen 
 to be made up of, first, a clear colourless fluid ; and, 
 secondly, of a multitude of small solid bodies or corpuscles, 
 which float in the plasma. This plasma, called liquor 
 sanguinis, is composed of water richly charged with 
 materials derived (through the chyme) from the food — 
 namely, albumin, globulins, various fats, &c. The greater 
 part of the blood — about 70 per cent. — is made up of 
 water. In 100 parts of blood by weight, we find 60 to 65 
 of-plasma and 30 to 40 of corpuscles. 
 
 108. Microscopical Appearance of Blood. — The 
 great majority of the corpuscles are of a yellowish-red 
 colour, and, by, their enormous number, impart a red hue 
 to the blood ; while a few are white or colourless. The 
 
ELEMENTARY HUMAN PHYSIOLOGY. 
 
 red corpuscles in man have a diameter of about -j^Vrth of an 
 inch, being about ;Jth of that fraction in thickness ; in form 
 they are circular biconcave discs (fig. 65, a), and in freshly- 
 drawn blood they arrange themselves, by contact of their 
 flattened surfaces, into rolls like piles of coins (fig. 65, e). 
 The colourless corpuscles are larger, globular or irregular 
 in form, and present a granulated appearance (fig. 65, d). 
 It is well known that these are little masses of living 
 protoplasm, capable of spontaneous movement, and that 
 they are identical with the corpuscles found in purulent 
 
 Fig. 65. — Blood- corpuscles : 
 I, two coloured corpuscles showing 
 shadowed appearance in the centre, 
 indicating biconcave rorm ; d, corpuscle 
 seen edgeways ; f, slightly oval cor- 
 puscle ; df colourless corpuscle ; gf 
 coloured corpuscles in rouleaux. 
 
 Fig. 66. — Blood-corpuscles of 
 various Animals magnified to 
 the same scale : 
 
 a, from proteus ; b, salamander ; c, frog ; 
 d, frog after addition of acetic acid, 
 showing nucleus ; s, bird ; y, camel : 
 g, fish ; ht crab or other invertebrate 
 animal. 
 
 matter or pus. In all classes of animals the colourless 
 corpuscles are alike ; but the form of the coloured cor- 
 puscles varies, being oval in fishes, reptiles, and birds 
 (fig. 66). In all mammals they are circular, with the ex- 
 ception of the camels and llamas, where they are oval (fig. 
 66, /). The red corpuscles are more numerous than the 
 white, being in the proportion of about 400 to i. In a 
 cube -^th of an inch on the side, there may be in normal 
 blood about 5jOoo,ooo red corpuscles. 
 
 109. Blood-corpuscles of Various .Animals.— The 
 coloured blood-corpuscles of all mammals have no nucleus, 
 
THE BLOOD. 1 03 
 
 swell up and become globular on the addition of water, and 
 almost entirely disappear in weak acetic acid. The coloured 
 corpuscles of birds, reptiles, and fishes have a nucleus which 
 is readily seen on the addition of water or acetic acid. Acetic 
 acid renders the body of the colourless corpuscle clear and 
 transparent, and reveals the existence of a peculiarly shaped 
 nucleus, as if several small granules or nodules adhered to- 
 gether. 
 
 no. Chemical Constitution of Plasma. — The 
 plasma is alkaline, yellowish in colour, and its specific 
 gravity is about 1026 to 1029. In loo parts of plasma, we 
 find of water, 90-2, and of solids, 9-7. The composition 
 of the solids is approximately as follows : Proteids : (i) 
 fibrin, -4; and (2) other proteids, chiefly serum albumin, 7-8 ; 
 extractives, -56; and inorganic salts, -85. Thus plasma con- 
 tains 10 per cent, of solids, of which 8 per cent, are pro- 
 teids. The specific gravity of pure blood is as high as 1050. 
 
 III. Coagulation or Clotting of the Blood. — 
 Shortly after its removal from the body, the blood begins 
 to thicken or coagulate, and soon separates into two distinct 
 parts, one of them being a dark-red jelly or clot, which is 
 the heavier of the two, and sinks ; while the other is a clear, 
 straw-coloured fluid, called the serum, which covers the 
 clot. This depends on the formation of a substance called 
 fibrin, which forms a meshwork of fine molecular fibres, 
 entangling the corpuscles. When a coagulum appears, 
 fibrin is produced by the action of an enzyme, or ferment- 
 like body, on a proteid substance called fibrinogen. 
 Fibrinogen belongs to the class of proteids called globulins, 
 distinguished from albumins by being insoluble in water, 
 while they are soluble in a weak solution of common salt. 
 It is probable that the ferment decomposes fibrinogen 
 into two parts : (i) another globulin that remains in 
 solution, and (2) the insoluble body fibrin. The ferment 
 itself is also a peculiar kind of proteid, and is believed to 
 
104 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 come from the colourless corpuscles. Coagulation may be 
 thus represented : 
 
 Blood i^'^'"^ {librtoXf,, , 
 ( CoipuBcles / ^^°^- 
 
 Clotting is hastened by (i) a temperature a little above that 
 of the body, (2) contact with foreign matter; and (3) 
 agitation; and it is hindered or prevented by (i) cold, 
 (2) contact of living walls of blood-vessels, and (3) addition 
 of solutions of sulphate of magnesia or sulphate of soda. 
 
 112. Other Chemical Substances in Blood. — These 
 are small quantities of sugar, cholesterin, soaps, and fats ; 
 traces of urea, uric acid, kreatin, &c. The most abundant 
 salt is chloride of sodium, or common salt, being about 90 
 per cent, of the total saline matters. 
 
 113. Chemical Composition of Corpuscles. — One 
 hundred parts of red blood-corpuscles contain of water 68'8 
 parts, and of solids about 3 1 parts — the solids contain 30-3 
 of organic matter, and about -8 of inorganic. The chief 
 organic substance is haemoglobin, the pigment of the blood. 
 One hundred parts of (fried corpuscles contain of proteid 
 •5 to I '2 parts, of haemoglobin 8'6 to 9-4, of lecithin (a 
 fatty nitrogenous matter containing phosphorus) -18, and 
 a trace of cholesterin. Haemoglobin is of special import- 
 ance, because, by uniting with oxygen to form oxy-haemo- 
 globin, it acts as the oxygen carrier in respiration. 
 
 Questions. 
 
 107, III. Describe the appearance of blood to the naked eye immedi- 
 
 ately after it has been shed, and half an hour thereafter. 
 
 108. What is the appearance under the microscope of a drop of 
 
 human blood ? Compare the red blood-corpuscles of a man 
 with those of a camel, a bird, a reptile, and a fish. 
 
 1 10. Give a short account of the chemical composition of the blood. 
 
 III.' What conditions hinder, and what conditions quicken, the clotting 
 of blood ? 
 
 113. What substances are found in a red blood-corpuscle ? 
 
loS 
 
 CHAPTER II. 
 
 CIRCULATION OF THE BLOOD. 
 
 114. The blood is in constant motion in a definite direc- 
 tion during life, and the motion is known as the circulation. 
 Its true course was discovered by Harvey, about 1620. 
 The organs of circulation are the heart, arteries, veins, and 
 capillaries. We will first briefly describe the structure of 
 these, and then treat of the mechanism of the circulation. 
 
 115. The Structure of the Blood-vessels. — Of these 
 there are three kinds — capillaries, arteries, and veins. The 
 
 Fig. 67. — Capillaries of 
 
 various size : 
 
 a, capillary much magnified and acted 
 
 on by nitrate of silver, so as to show 
 
 that it is made up of flattened cells ; 
 
 hi a smaller vessel showing the same ; 
 
 c, a small artery or vein showing 
 transverse and longitudinal nuclei ; 
 
 d, ultimate capillary from /?a mater 
 of sheep's brain. 
 
 capillaries are delicate tubes, about the diameter of a blood- 
 corpuscle (fig. 67, d\ apparently formed of transparent mem- 
 brane, with nuclei imbedded here and there in the wall ; but 
 they are composed of flattened cells, adhering edge to edge 
 
 Fig. 68. — An Artery of inter- 
 mediate size : 
 s, a, openings of branches and position 
 of lining of vessel ; ^, b, b, hiuscular 
 coat showing transverse nuclei : c, c, 
 coat of connective tissue. 
 
io6 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 (fig. 67, a, b). In vessels somewhat larger, we find outside of 
 the lining (which is composed of endothelial cells, see p. 86) a 
 delicate, transparent, and fragile membrane, which tends to 
 curl upon itself, from its elasticity. It is perforated by numerous 
 small holes. Outside of this there is a layer of muscular fibre- 
 cells arranged longitudinally and transversely, the nuclei of 
 which are seen after the addition of acetic acid (fig. 68). This 
 
 constitutes what is usually 
 termed the muscular coat. 
 g In large arteries, we find 
 outside of, and intimately 
 'd' connected with, the muscu- 
 lar coat a thick layer of 
 yellow elastic tissue, which 
 gives great elasticity to these 
 vessels ; and most externally 
 there is a layer of connec- 
 tive tissue. As the vessels 
 are traced towards their 
 capillary terminations, they 
 gradually lose their, connec- 
 tive tissue and elastic coats. 
 In small arteries, called 
 
 Fig. 69.- 
 
 -Diagram of Heart halved 
 and laid open : 
 
 . o o T-v ■ c . r.>-™.™j arterioles, the wall is com- 
 
 A, B, C, D, as in fig. 70. a, part of tricuspid » 
 
 valve; b, part of mitral; c, semilunars at pOSed entirely of two layers 
 base of pulmonary artery, a', a', inferior of longitudinal and circular 
 and superior venpcav^ entering A ;*-,«■ n^us^ular fibre-cells, hned 
 pulmonary arteries proceeding from B, j,.,., n j- 
 
 c-,./, aorta proceeding from C ;<?,<?, pul- by endothelial cells, and in 
 monary veins entering D. the ultimate capillary these 
 
 fibre-cells have disappeared, and there is only a thin wall 
 formed of endothelial cells, as above described. Veins differ 
 from arteries chiefly in the comparative thinness of their coats. 
 It is important to bear in mind that the predominant feature 
 of the larger arteries is elasticity, while that of the smaller is 
 contractility. The ultimate capillaries are also independently 
 contractile. 
 
 116. The Position and Structure of the Heart. — 
 This organ is situated in the thorax or chest, between the 
 two lungs, and, together with portions of the great vessels 
 
CIRCULATION OF THE BLOOD. 
 
 107 
 
 which convey blood to and from it, is inclosed in a 
 membranous bag, the pericardium. It is a hollow organ, 
 having muscular walls. The following anatomical points 
 may be clearly made out on the heart of an ox or of a 
 sheep, a demonstration of which will teach far more than 
 we can hope to explain in these pages. It is divided 
 (fig. 69) by a septum into a right and left half, each of 
 which is again subdivided 
 by a transverse partition 
 into two compartments, com- 
 municating with each other, 
 named the auricle. A, D, 
 and ventricle, B, C. The 
 apex of the heart may be 
 felt in the living man be- 
 tween the cartilages of the 
 fifth and sixth ribs, a little 
 below, and to the inner side 
 of, the left nipple. 
 
 The heart is a double 
 organ, composed of a right 
 and left part, each consist- 
 ing of an auricle and ven- 
 tricle. These are named, 
 in the order in which the 
 blood passes through the 
 heart, right auricle, A ; right 
 ventricle, B; left auricle, D; 
 and left ventricle, C. Into 
 the right auricle, blood passes by the following openings ; 
 (i) from the head, neck, and upper extremities by the 
 superior vena cava, a'; from the lower part of the body 
 by the inferior vena cava, a, and from the wall of the 
 heart itself by numerous small veins. The blood passes 
 from the right auricle to the right ventricle through an 
 
 Fig. 70.— Section of the Human 
 Heart : 
 A, right auricle ; B, right ventricle ; 
 C, left ventricle ; D, left auricle ; E, 
 partition between the two ventricles. 
 Between the auricles and ventricles on 
 right and left, the tricuspid and mitral 
 valves with their cords and muscular 
 papillse are shown. 
 
I08 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 opening in the partition between the auricle and ventricle 
 known as the right auriculo-ventrkular opening, which is 
 guarded by a valve called the tricuspid valve (fig. 69, a). 
 From the right ventricle the blood is sent to the lungs 
 through the pulmonary artery, b', and it is returned from 
 the lungs to the left auricle by four pulmonary veins, d', 
 and from thence to the left ventricle through an open- 
 ing in the septum between the auricle and ventricle, called 
 the left auritulo-ventricular opening {b), where we find a valve 
 corresponding to the tricuspid on the right side, but com- 
 posed of two flaps instead of three, and hence called the mitral 
 ^„,„__^ valve, from its fancied 
 
 /^^^^^^S^^^^^^^. resemblance to the 
 "• f^U^K, ■■ " \. ^B * ^PP^"" P^'^' ^'^ ^ bishop's 
 
 (fj^P*^/K'" \^^^J ~M ™itre. "At, or a little 
 \^^ M|p ^ ^^^^^^Bfegy above, the orifices of 
 
 N. ^?i^^^^^5\ and of the aorta, we 
 
 ^^^^^ mB'/y c find valves which, from 
 
 ^"*;iiJ^Bi/ their shape, are termed 
 
 Fig. 71.-Section through the Heart at j^e semilunar valves. 
 the level of the valves. _ ^ __ , „. 
 
 „, , . ^., ... ... See figs. 70 and 71, 
 
 The tficusptd^ a, is seen in the upper left corner, ° , _ ' 
 
 ihe miirnl, i, in the right, and below, the two aild description. 
 semihtiiar valves, c, c, at the orifices of the The Substance of 
 
 aorta and pulmonary artery. 
 
 the heart is composed 
 of a spiral arrangement of seven layers of muscular fibre. 
 When the ventricles contract, \frhich they do simultaneously, 
 the blood is propelled from them with a sort of spiral 
 motion, as if it were wrung out of the heart. The simul- 
 taneous contraction of the two auricles is much more gentle. 
 117. General Description of the Course of the 
 Circulation. — This may be studied with the aid of a 
 diagram (fig. 72), which is equally applicable for all other 
 mammals as well as for man and for birds. The parts of 
 fig. 72 in black represent structures filled with impure or 
 
CIRCULATION OF THE BLOOD. 
 
 109 
 
 venous blood, while the clear or white parts represent struc- 
 tures in" which pure oxygenated arterial blood occurs. 
 Observe in fig. 69 the four cavities, A, B, C, D, of which 
 the heart is composed. Two of these cavities, A and D, 
 are for the purpose ■ of receiving the blood as it flows into 
 the heart, and are 
 termed the auricles ; 
 while the two cavities, 
 B and C, are for the 
 purpose of propelling 
 the blood through the 
 lungs and the rest of the 
 body respectively, and 
 are termed the ventricles. 
 The vessels that trans- 
 port blood into the 
 auricles are termed 
 veins; and the vessels 
 through which blood is 
 driven onwards from the 
 ventricles are known as 
 arteries. The diagram 
 (fig. 72) further shows 
 that what we commonly 
 term the heart may be 
 regarded as two distinct 
 hearts in apposition with 
 
 each other; one, black in The arteries are shown white, and the veins 
 
 . , ^ .... Ill black. 1^, aorta ; ^, right, and c, left lung ; d^ 
 
 the figure, whlchlS called ;„,„;„, ^^na cava ; e, liver ; f, portal vein ; 
 
 the right, or venous, or e> digestive organs. 
 
 pulmonary heart; and the other, white, called the left, or 
 arterial, or systemic heart, the last name having been given 
 to it because the blood is sent from it to the general 
 system ; just as the right heart is termed pulmonary because 
 it sends blood to the lungs. 
 
 Fig. 72. — Diagram of tlie Circulation. 
 
no ELKMENTARY HUMAN PHYSIOLOGY. 
 
 1 18. We shall now trace the course of the blood as 
 indicated by the arrows in the diagram (fig. 73), com- 
 mencing with the right auricle. The right auricle, con- 
 tracting upon the venous or impure blood which has been 
 returned from the body, and with which we suppose it to 
 be filled, drives its contents onwards into the right ventricle, 
 through an opening between these two cavities, called 
 the right auriculo-ventricular opening, which is guarded by 
 a valve, named tricuspid, from its being composed of three 
 pointed membranous expansions, which almost entirely 
 
 LI \J 
 
 Fig. 73.— Scheme of Course of Blood through Heart and Lungs: 
 a, arch of aorta ; 3, b, lungs : c, heart ; d, aorta ; e^ inferior vena cava. 
 
 prevents the regurgitation or reflux of the blood from the 
 ventricle into the auricle (figs. 70 and 71). The ventricle 
 being now filled, contracts ; and, as the blood cannot return 
 to the auricle, it is driven along the vessel (shaded in fig. 
 73), the pulmonary artery, which conveys the blood to 
 the lungs. At its commencement it is guarded by valves, 
 
CIRCULATION OF THE BLOOD. Ill 
 
 termed, from their shape, the semilunar pulmonary valves, 
 which entirely prevent the blood that has been once 
 propelled into the pulmonary artery from re-entering the 
 ventricle (figs. 71 and 74). The pulmonary artery gradu- 
 ally divides into smaller and smaller branches, ultimately 
 merging into capillaries. In the capillaries, freely dis- 
 tributed over the external surface of all the air-cells (of 
 which the lung is mainly composed), the venous blood is 
 brought into contact with atmospheric air, gives off its 
 carbonic acid gas (its principal impurity), 
 and absorbs oxygen, by which processes 
 it is converted into pure or arterial 
 blood. The capillaries, in which the 
 blood is arterialised, gradually unite to 
 form minute veins, which, again, join to Fig. 74. — Semi- 
 form larger vessels, until finally the blood '""^'' Valves of 
 is collected into four vessels, known as ^°''"' ''"f ^"'" 
 
 , . , , ^ monary Artery. 
 
 pulmonary veins (two from each lung), 
 
 discharging their contents into the left auricle. The blood, 
 
 now fitted for the various purposes of nutrition, enters the 
 
 left auricle, which, by its contraction, propels it into the 
 
 left ventricle, through the left auriculo-ventricular opening. 
 
 This opening, like the corresponding one in the right heart, 
 
 is guarded by a valve, from its form termed the mitral 
 
 valve, which entirely prevents the reflux of the blood. The 
 
 left ventricle contracts, and drives its contents into the 
 
 large artery (fig. 73, a), the aorta — the great trunk — which, 
 
 by means of its various branches, supplies every portion 
 
 of the body with pure arterial blood. See figs. 75 and 
 
 76, and description. 
 
 119. From the aorta and its various subdividing branches, 
 
 many of which are seen in fig. 75, the blood passes into 
 
 the capillaries, which occur in every part of the system (fig. 
 
 77). In these capillaries it undergoes important changes, 
 
 which may be considered as almost the reverse of those 
 
ELEMENTARY HUMAN PHYSIOLOGY. 
 
 occurring in the pulmonary capillaries ; it parts with its 
 oxygen, becomes charged with carbonic acid, and, as it 
 leaves the capillaries and enters the minute veins formed by 
 their union, presents all the characters of venous blood. The 
 veins gradually unite till they form two large trunks, termed 
 the superior and inferior vence caves (fig. 75, *, 4), which pour 
 
 12 k 
 
 Fig. 75. — Diagram of the Aorta, 
 with its principal Branches : 
 
 A, ascending part of the arch of the aorta; 
 a, thoracic aorta ; &&, abdominal aorta ; 
 c, dy right and left ventricles of heart ; 
 e,y, right and left auricles of heart ; g, h^ 
 right and left pulmonary arteries ; z, k, 
 right and left common carotid arteries ; 
 I, m, right and left subclavian arteries ; 
 «, hepatic artery ; o, gastric artery ; jS, 
 splenic artery ; q, r, right and left renal 
 arteries ; a; t, superior and inferior 
 mesenteric arteries; u, v, right and left 
 common iliac arteries ; w, middle sacral 
 artery ; jt, phrenic arteries ; y, spermatic 
 arteries. 
 
 I, superior vena cava ; 2, right internal 
 jugular vein ; 3, right subclavian vein 
 (the left is removed to show the arch of 
 the aorta); 4, inferior vena cava; 5, 6, 
 right and left pulmonary veins ; 7, hep- 
 atic veins ; 8, g, right and left renal 
 veins; 10, 11, right and left iliac veins; 
 12. trachea. 
 
 their contents into the right auricle — the point from which 
 we started. We thus perceive that there is a complete 
 double circulation; that there is a lesser circulation effected 
 by the blood in its passage from the right to the left heart 
 through the lungs, and that there is a great circulation 
 effected by that fluid in its passage from the left heart, 
 through the system generally, to the right heart. 
 
 1 20. Influence of Elasticity of the Great 
 Arteries, and of the Contractile Coats of the 
 
CIRCULATION OF THE BtOOD. 
 
 "3 
 
 Small Arteries, on the Circulation. — But although 
 the heart is the chief organ for propelHng the blood, there 
 are other forces at work. When the left ventricle con- 
 tracts, blood is propelled into the aorta, which, however, 
 contains blood at the time. 
 This blood is pushed for- 
 wards, and the aorta dilates. 
 When the propulsive power 
 has ceased, the aorta, being 
 a very elastic tube, recovers 
 its original calibre. In doing 
 so, it assists in forcing the 
 blood onwards. Thus, by 
 successive portions of the 
 larger arteries acting in the 
 same manner, dilating with 
 the impulse, and regaining 
 their size by elasticity, the 
 original mechanical force of 
 the heart, which throws 
 blood into the aorta in a 
 series of successive jets, is 
 converted into a uniform 
 wave-like movement, sent 
 along the walls of the arteries, 
 which we term the pulse. 
 The pulse, which beats about 
 seventy times per minute, is pig. 76.-The Arterial System: 
 
 the change produced in the a, temporals; ^, carotid ;c, artery of arm; 
 
 diameter and length of an 
 artery when it receives the 
 wave of blood. The effect of the elasticity of the vessels 
 is to convert the sudden spasmodic action of the contrac- 
 tion of the ventricle into a continuous uniform movement. 
 Hence in the capillaries, as seen in the web of a frog's 
 
 H 
 
 d, aorta ; £■, kidney ; f^ artery of thigh 
 (femoral). 
 
114 
 
 ELEMENTARY HtTMAN PHYSIOLOGY. 
 
 foot, there is no jet-like movement, but the blood flows 
 
 onward in one continuous stream. The smaller arteries, 
 
 arterioles^ possess a thick muscular coat, and this coat is 
 
 kept in a state of partial contraction, by which their calibre 
 
 is diminished. The effect of 
 
 this is to keep the arterial 
 
 system, as it were, overfull, 
 
 because the blood thrown into 
 
 the aorta and great arteries by 
 
 each stroke of the heart does 
 
 not at once rush through the 
 
 capillaries into the veins. 
 
 Suppose a long, elastic india- 
 
 „. _„ rubber tube, with a stop-cock 
 
 Fig. 77, 
 
 ^ . . r . ,^^■ n ■ ^t onc end and a force-pump 
 
 Termination of artery (A) in capillaries '■ ^ 
 
 (C), and those in vein (V). at the Other. If wc drive 
 water by the pump in at one end, the water might rush 
 out at the other end to the same amount. This would 
 be the case if the stop-cock were wide open ; but if we 
 partially turned off the stop-cock, then the water would not 
 run out so quickly, and the tube would become distended. 
 The same thing occurs in the arteries during life. The 
 great arteries are always overfull, and their walls are dis- 
 tended. Consequently, there is always a considerable 
 pressure in the great arteries. This pressure is shown if 
 an artery is punctured. The blood then comes out with a 
 spurt or jet. This pressure is called blood pressure. It is 
 greatest in the large arteries, and becomes less and less as 
 we pass onwards. It is smaller in the capillaries, and still 
 smaller in the veins. 
 
 It is also important to notice that the force of the 
 elasticity of the great vessels always comes into play during 
 the intervals between the heart-beats. Thus, in the first 
 place, the blood is driven onwards by the force of the heart- 
 beat, or, in other words, by the contraction of the left 
 
CIRCULATION OF THK BLOOD. II5 
 
 ventricle. This force also partially distends the arteries, 
 and these rebound during the relaxation of the ventricle, 
 and the elastic rebound or recoil forces the blood on- 
 wards while the ventricle is distending. 
 
 We must carefully distinguish between the velocity of the 
 pulse-wave and the velocity of the current of the blood. 
 Suppose a river flowing slowly along in one direction. We 
 might, by a dip of an oar, cause a wave to travel on the 
 water in the same direction as the stream was flowing ; 
 but the rate at which the wave travelled would be much 
 faster than the rate of flow of the river. The same happens 
 in the case we are considering. The pulse-wave travels 
 along the walls of the arteries much faster than the blood- 
 stream. The blood-stream is fastest in the great vessels, 
 and slowest in the capillaries. While the blood passes 
 along the veins the stream again flows faster as these be- 
 come wider and wider. In addition to this, the blood is 
 sucked onwards towards the heart by the action of the 
 auricle, and by the inspiratory movements. 
 
 The tissues also exert a feeble attractive influence on the 
 blood, drawing it forwards ; and 
 consequently we find that, wher- 
 ever we have activity of growth in 
 any part of the body, there is a 
 determination of blood to that 
 part. We see this in the conges- 
 tion which precedes the "annual 
 growth of a stag's horn. 
 
 121. Action or the Veins. — 
 After the blood has passed through 
 the capillaries into the veins, the 
 power of the heart has reached a 
 minimum. The blood is now forced along the veins to 
 the heart, chiefly by the pressure of the muscles. Many of 
 the veins are provided with valves, which are so arranged 
 
 Fig. 78. 
 Valves in Veins : 
 :, vein slit open, showing semi- 
 lunar valves ; ^, side view, show- 
 ing the valves closed ; c, vein 
 with swelling at valves. 
 
ii6 
 
 ELEMENTARY HUMAN PHYSIOLOGy. 
 
 Fig. 79.— Mode 
 Action of Valve 
 
 of 
 
 as to allow the blood to flow only towards the heart ; and, 
 consequently, when a muscle contracts and presses on a 
 vein, the blood is propelled forwards (figs. 78, 79.) 
 
 122. Influence OF Respiration. — 
 Lastly, the movements of respiration 
 affect the circulation ; inspiration, by 
 increasing the flow of blood along the 
 great vessels to the heart ; while expira- 
 tion has the contrary effect. By inspira- 
 tion the cavity of the chest is increased, 
 ^, and pressure is removed from the sur- 
 
 shut : o, open. No ^ 
 
 backward flow possible faccs of the heart and great veins. Hence 
 '" "• the pressure on these surfaces becomes 
 
 less than atmospheric 
 pressure, and as atmo- 
 spheric pressure acts 
 on the veins outside 
 the chest, the blood is 
 driven onwards to the 
 heart. In other words, 
 it is sucked or aspir- 
 ated. Expiration has 
 the contrary effect. 
 
 123. Rhythmic 
 Movements of the 
 Heart. — The auricles 
 contract synchronously 
 — that is, at the same 
 time, and pour their 
 blood into the ven- 
 tricles. When these 
 are full, they also 
 contract synchronously, 
 the right sending blood 
 to the lungs, and the left to the body. 
 
 124. Conditions affecting the Pulse. — Muscular 
 
 Fig. 80. — The 
 Veins of Arm, as 
 in the operation 
 of bleeding. 
 
 The bandage above 
 the elbow prevents 
 the blood flowing up 
 the veins. These are 
 seen distended. By 
 working the fingers 
 round the rod (the 
 representative of the 
 barber's pole), the 
 blood is driven more 
 X and more to the dis- 
 tended veins. A vein 
 is then opened at 
 the bend of the 
 elbow. 
 
 a, a, valve. 
 
CIRCULATION OF THE BLOOD. II7 
 
 exertion, if violent, quickens the pulse. It is more 
 frequent in the erect than in the sitting position, and 
 quicker then than in the recumbent posture. Sex appears 
 to exercise an influence. The natural pulse in the adult 
 male varies between 60 and 70 pulsations per minute, 
 that of the female being on an average about 10 beats 
 more. In the newly born infant it is from 130 to 140 ; 
 in old age, from 50 to 60 ; but occasionally in old age it 
 is much more rapid. The pulse is quicker in the morning 
 than in the evening ; it reaches its maximum about noon, 
 and its minimum soon after midnight. The pulse is 
 quickened by excitement, and sometimes slowed by fear. 
 It is quickened in most diseases, especially so in those of a 
 febrile character ; but it is slowed usually in jaundice and 
 in cases of compression of the brain. 
 
 125. Circulation in the Capillaries. — Few sights 
 are more beautiful than the circulation of the blood in the 
 web of a frog's foot. The blood flows 
 in a continuous stream, the coloured 
 corpuscles in the centre of the vessels, 
 while the colourless (much fewer in 
 number) may be observed travelling j 
 more slowly, especially after irritation 
 of the part, at the side of the current, 
 ahd occasionally clinging to the wall | 
 of the vessel. It has been estimated 
 
 that the blood flows in the capillaries Fig. 81. -Arrangement 
 at the rate of about i inch per minute. °^^^^^^^ thSill"^ 
 In an artery it runs probably about 
 15 inches per second, and slower in a vein. The arrange- 
 ment of the capillaries of the skin are seen in fig. 81. 
 Each tissue and organ has its characteristic arrangement 
 of these small vessels. 
 
Il8 ELEMENTARY HUMAN PHYSiOLOfiV. 
 
 Questions. 
 
 114. Who was the discoverer of the circulation of the blood? 
 
 1 15. Describe the structure (a) of a capillary, (6) of a small artery, and 
 
 (c) of a vein. 
 
 116. Describe the position of the heart in the thorax, mentioning the 
 
 vessels connected with it at its base. What structures are seen 
 in the right ventricle and in the left ventricle ? Describe and 
 draw the semilunar valves at the orifice of the aorta. 
 
 117. Describe the course of the Circulation, beginning at the right 
 
 auricle. What do you mean by the pulmonary circulation? 
 
 118. When the ventricle contracts, how is the blood prevented from 
 
 passing back into the auricle, on the right side ? 
 118, 119. During what time of the heart's action are all the cavities 
 filling with blood ? 
 
 120. What is the influence of the elastic coat in the greater arteries on 
 
 the circulation? Show how it is that during life we may 
 regard the arteries as always overfull. What is meant by 
 blood- pressure ? Why is it high in the arteries? How does 
 the contractile coat of the smaller arteries affect the circulation ? 
 
 121. Draw a diagram showing the action of the valves in veins. 
 
 122. How does inspiration affect the circulation? 
 
 1 24. What conditions influence the rate of the pulse ? 
 
 125. Describe the circulation in the capillaries. 
 
 CHAPTER III. 
 
 T//E ALIMENTARY SYSTEM. 
 
 126. General View. — This function is a complex pro- 
 cess. To keep up the integrity and vigour of the body, 
 food must be procured, chewed or masticated, mixed with 
 saliva, swallowed, digested in the stomach, the nutritious 
 material absorbed by special organs in the bowels, called 
 villi, and from these carried to various glands, where it is 
 elaborated into blood. The blood is then conveyed through 
 the body, giving up to the tissues what they require for 
 nourishment, and carrying away materials resulting from 
 
THE ALIMENTARY SYSTEM. II9 
 
 their decay. Thus rendered impure, the blood must have 
 the noxious materials removed. For this purpose, several 
 organs, such as the lungs, the liver, the skin, the kidneys, 
 and the lower bowel, are set apart. Thus the blood is 
 constantly replenished with nutritious matters, and con- 
 stantly being purified, so as to fit it for supplying each 
 individual cell of the body with exactly the material it 
 requires. Bone selects earthy salts, muscle needs albumin, 
 the nervous system requires fatty matter, and so on. 
 
 The general arrangement of the alimentary canal is 
 
 Fig. 82. — Diagram of a Vertebrate Animal : 
 
 «, mouth ; b, b, teeth ; c, olfactory nerve ; d, optic nerve ; e, palate ; /^ epi- • 
 glottis ; g;, oesophagus, or gullet : h^ cerebrum, or great brain ; z, cerebellum, or 
 lesser brain ; j\ external ear ; k, trachea, or windpipe : /, lung ; wz, heart ; 11, 
 diaphragm : o, liver ; p, stomach ; y, pancreas ; r, small intestine ; s, kidney; /, 
 spleen ; u, bladder ; f , anus ; w, testicle ; ;r, jr, spinal cord ; y, y, processes of 
 vertebrae : z, muscle. A, A, bones of legs ; B, foot ; C, hind-leg. 
 
 seen in fig. 82, representing an ideal longitudinal section 
 of a vertebrate animal ; fig. 29, p. 36, should also be 
 studied. 
 
 The process of nutrition is complex only in the higher 
 animals. In the amoeba (fig. 83), a little animal which is 
 nothing more than a mass of jelly-like living material, con- 
 taining a nucleus, nc, and often small contractile bags or 
 vacuoles, vc, we find no trace of organs, and nutrition is 
 carried on by any part of the body. A little fragment of 
 nutritious matter may be surrounded by the protoplasm of 
 the body of the animal, and by it is also converted into 
 
1 !*! ■ 
 
 120 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 protoplasm, vc. But as we ascend in the scale of animal 
 life, one organ after another is added, such as a digestive 
 sac, glands for secretions to act on the food, a special fluid 
 — the blood, an organ and vessels for circulating this fluid ; 
 and so on, till we come to the higher animals, where we 
 find a complex system in operation. 
 
 Fig. 83.— Aihoeba. 
 i, amceba with blunt processes, nucleus, nc ; contractile vacuoles, vc ; food vacu- 
 oles and granules. 2, two daughter amcebEe. 3, amceba in process of dividing. 
 4, encysted phase, with inclosed diatoms, &c. 
 
 Question. 
 
 126. Describe generally the process of nutrition, 
 nutrition, as carried on by an amceba. 
 
 Give an account of 
 
 FOOD OR ALIMENT. 
 
 127. Necessity for Food. — A living being is always 
 in a state of change. His skin gives off water, either in the 
 form of sweat or as an invisible vapour ; his kidneys also 
 separate water, the water in both cases containing salts and 
 other matters in solution ; and his lungs are always exhaling, 
 not only watery vapour, but the gas known as carbonic acid, 
 as may be readily shown by breathing into lime-water, 
 
THE ALIMENTARY SYSTEM. 121 
 
 which soon assumes a milky appearance, in consequence of 
 the formation of carbonate of lime. Moreover, as has 
 already been shown, the body, which has an almost con- 
 stant temperature of about 98-4° F., is always giving off 
 heat, so that if a man were surrounded by ice, part of the 
 ice would be melted, and the amount of heat might be 
 estimated by the weight of water produced. The produc- 
 tion of heat indicates chemical changes in the body, accom- 
 panied by waste of material. In addition, there is a con- 
 stant expenditure of energy in carrying on the internal work 
 of the body, or in doing the daily outside work of life. If 
 this condition of things were to go on indefinitely, the 
 weight of the body would gradually diminish, and the person 
 would become weaker and weaker. To retain the body 
 in an efficient state both as regards matter and energy, 
 it must be supplied with atmospheric air, water, and 
 food. We have placed these in the order of their import- 
 ance. 
 
 128. Physiological Importance of the Air. — The 
 atmosphere consists of a mechanical mixture of 4 parts of 
 nitrogen and i part of oxygen. In 100 volumes of air (say 
 100 cubic inches), there are 20-81 of oxygen and 79- 19 of 
 nitrogen. By weight, in 100 parts, there are 23-01 of oxygen 
 and 76-99 of nitrogen. In addition, the air always contains 
 a small amount of carbonic acid (about 4 parts in 10,000 
 parts), a small quantity of an element called argon, a vari- 
 able but minute trace of ammonia, traces of nitric acid, and 
 frequently in towns traces of sulphurous acid and sul- 
 phuretted hydrogen. Finally, it contains variable quantities 
 of aqueous vapour. The constituent of greatest importance 
 in the economy of the body is oxygen. Without this gas, 
 life cannot be prolonged for more than a few minutes. 
 Consequently, there are special arrangements for intro- 
 ducing it into the body. This constitutes part of the process 
 of respiration. 
 
122 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 129. Physiological Importance of Water. — When 
 we recollect that water is present in every tissue of the 
 body, and especially in those tissues which are of the 
 greatest importance to life, such as brain or muscle, we see 
 at once the importance of a due supply of this fluid. The 
 presence of water is a condition of all vital activity. It is 
 the solvent by which substances are brought into close 
 contact with each other, and it is the medium in which all 
 those molecular processes occur on which life depends. It 
 is remarkable, too, that it is in a constant state of transi- 
 tion in the body, and as it is continually being given off, 
 it must be replenished. Hence all animals introduce into 
 the body water, either as such, or combined with the 
 food. 
 
 130. Classifications of Food. — Various classifications 
 of the food of man have been proposed ; but the following 
 is simple and practical : The aqueous ; the albuminous ; the 
 fatty, oily, or oleaginous ; the starchy and saccharine ; the 
 gelatinous; and the saline groups. All our daily food is 
 referable to one or more of these classes. The aqueous 
 group includes not only water, but all fluids (except oils) 
 used as drink, and it must be recollected that so-called 
 solid foods contain a large percentage of water. The 
 albuminous group is typified by the white of egg, and in- 
 cludes the gluten of flour and the chief constituents of 
 flesh and cheese. The albuminous foods chiefly nourish 
 the muscles, but they contribute, along with fat or oil, to 
 almost every tissue. The fatty group includes all animal 
 and vegetable fats or oils. The starchy and saccharine 
 group contains all the varieties of sugar, starch, dextrin, and 
 gum. The starches and sugars belong to the group of 
 carbo-hydrates (see p. 57). This group is largely used by the 
 muscles, and to some extent they form fat. The gelatinous 
 group is represented by cow-heel, isinglass, and such-like 
 substances, yielding jellies and soups that stiffen on cooling; 
 
tME aLIMenTarV sVsteM. 123 
 
 while the saline group includes mineral matters, especially 
 common salt, and phosphates of the alkalies, and of lime, 
 &c. The saline or mineral matters form bone, tooth, &c., 
 and they are found in variable proportions in almost every 
 fluid and solid in the body. It must be remembered, how- 
 ever, that a mixture of all of these constituents of food is 
 essential to the formation of a nutritious diet, and, more- 
 over, that there must always be a certain amount of sapidity 
 or flavour in the food. We should turri with disgust from 
 a mess consisting of these constituents, even in proper pro- 
 portions, if it were not palatable or tasty. The best 
 example of a natural food is milk. It contains water, 
 albumin in the form of casein (the chief constituent of 
 cheese), fat in the form of cream (or butter), sugar, and 
 various salts. Hence it is nature's food for all young 
 animals of the mammalian group. 
 
 131. Conditions DETERMINING THE quantity of Food. 
 — These are : (i) the amount of oxygen in the atmosphere 
 and the temperature ; (2) the amount of mental and bodily 
 exertion and (3) the activity of growth. Exercise and 
 exposure to cold sharpen the appetite, and thus lead to 
 more food being taken. It is also well known that dwellers 
 in the arctic regions not only eat a great deal of food, but 
 of that kind which, by oxidation by the oxygen of the air, 
 is heat-producing — namely, oleaginous matter. On the 
 other hand, the inhabitants of the tropics eat sparingly, 
 and chiefly of products rich in carbo-hydrates, such as 
 starch, sugar, &c. In a temperate clime, something be- 
 tween the two extremes is found to be most conducive to 
 health. 
 
 132. Food and Work.— It is evident that the amount 
 of food must have some relation to the work done by 
 the individual. Hard work means expenditure of matter 
 and energy, and these must be supplied by food. The fol- 
 lowing table shows the quantities, in ounces avoirdupois, of 
 
124 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 the different materials of dry food required under different 
 circumstances : 
 
 Nature of the Diet. Nitrogenous p^, ^Carbo- gaits. Total. 
 
 Bare subsistence diet 2-33 0-84 n-69 ... 14-86 
 
 Adult in full health, with 
 moderate exercise 4'2IS 1-397 18-960 0-714 25-286 
 
 Active labourer, not over- 
 worked '. 5-41 2-41 I7'92 0-68 26-42 
 
 Hard-working labourer, 
 navvy 5-64 2-34 20-41 0-68 29-07 
 
 Add to each of these from 60 to 80 ounces of water, 
 taken either alone or as part of the food in a succulent or 
 cooked state. Thus it would appear that in ordinary life, 
 and with a fair amount of labour to perform, a healthy adult 
 requires daily about 28 or 30 ounces of dry nutritious food, 
 along with about 70 ounces of water. 
 
 133. Different kinds of Food. — The nutritious value 
 of different articles of diet depends (i) on their digesti- 
 bility ; and (2) on the amount they contain of the proxi- 
 mate constituents which are required for nourishing the 
 body. There are great differences in the percentage com- 
 position of food, as may be seen in the following table : 
 
 TABLE SHOWING THE PERCENTAGE COMPOSITION OF VARIOUS 
 ARTICLES OF FOOD. 
 
 Nature of Food. Water. Albumin. Stan:li. Sugar. Fats. Salts. 
 
 Bread 37 8-1 47-4 3-6 1-6 2-3 
 
 Wheat flour 15 io-8 66-3 4-2 2-0 1-7 
 
 Oatmeal 15 12-6 58-4 5-4 5-6 3-0 
 
 Rice 13 6-3 79-1 0-4 0-7 0-5 
 
 Potatoes 75 2-1 i8-8 3-2 0-2 j3-7 
 
 Peas IS 23-0 55-4 2-0 2-1 2-5 
 
 New milk 86 4-1 ... 5.2 3-9 o-8 
 
 Cheese 36-6 33-5 ... ... 24-3 5-4 
 
 Beef 51 14-8 ... ... 29-8 4-4 
 
 Pork 39 9-8 ... ... 48-9 2-3 
 
 Poultry 74 21-0 ... ... 3.8 1-2 
 
 White fish 78 18-1 ... ... 2-9 l-o 
 
 Egg , 74 14-0 10-5 1-5 
 
THE ALIMENTARY SYSTEM. 1 25 
 
 A glance at the preceding table will also show that the 
 habit of combining different articles of diet, such as bread 
 and butter, beef and potatoes, chicken and ham, &c. is 
 physiologically correct. It also shows that oatmeal por- 
 ridge and milk make a highly nutritious diet. 
 
 Questions. 
 
 127. Show why food is necessary. 
 
 128. What is the composition of pure atmospheric air? 
 
 129. Why must water be taken daily into the body? 
 
 130. Classify foods. Give an example of each class. Why is a mix- 
 
 ture of food-constituents necessary for a healthy diet ? 
 
 131. What circumstances determine the quantity and quality of a diet? 
 133. Show why oatmeal porridge, beef and bread, bread and cheese, 
 
 and milk and bread form food diets. 
 
 We shall now describe the steps in the process of 
 digestion. 
 
 134. Mastication. — 
 Mastication is effected in 
 the cavity of the mouth 
 by means of the teeth, 
 which fit into sockets in 
 the upper and lower jaw- 
 bones (figs. 10 and 11, 
 and fig. 84). The up- 
 per jaw is immovable, 
 or only movable with 
 the entire head ; but the 
 lower jaw, with its teeth, 
 is capable of moving 
 upwards, downwards, 
 backwards, forwards, 
 and laterally, by means 
 of the powerful muscles 
 of mastication. It is by 
 the varied movements of the lower teeth against the upper. 
 
 Fig. 84. 
 
 a, the separate human teeth as they occur in 
 the half-jaw of the adult ; B, the human teeth 
 m situ in the upper jaw ; a, a, incisors ; 
 bf i, canines ; c, f , premolars ; d^ d, true 
 molars. 
 
126 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 through the action of these muscles, that food is broken 
 down or masticated. The tongue also, moved by its 
 muscles, gathers together the food from below the dental 
 arches, and crushes it against the palate. In the adult 
 there are 32 teeth, 16 in each jaw, and 8 on each side. 
 There are from before backwards, beginning in the middle 
 line of the jaw, 2 incisors or cutting teeth on each side ; 
 I canine or eye-tooth, for seizing ; 2 premolars or bicuspids, 
 for tearing; and 3 iholars or grinders, for crushing and 
 breaking up the food (fig. 84, A). The body and greater 
 
 Fig. 85.— Vertical Section through ^'S- 86. 
 
 a Tooth lodged in its socket : "■ '■'"^^'^ of enamel prisms : h, two 
 
 prisms isolated. 
 A, enamel ; b^ dentine ; f, crusta petrosa 
 
 or cement ; d^ lining of the cavity in the 
 gum ; f , bony socket in gum ; y, pulp- 
 cavity. 
 
 bulk of each tooth consists of substance called dentine (fig. 
 85, ^), composed of branching tubes; the top or crown is 
 covered by a cap of enamel^ a very hard substance, made 
 of small hexagonal prisms (fig. 85, a^ and fig. 86), and 
 the fang or root is protected by a layer of a material resem- 
 
THE ALIMENTARY SYSTEM. I 27 
 
 bling bone, called crusta petrosa or cement (fig. 85, c). 
 In the centre of each tooth there is a cavity containing 
 pulpy matter, in which are nerves and blood-vessels (fig. 
 85,/). 
 
 135. Insalivation. — Insalivation is effected by the 
 admixture with the triturated food of the secretions of 
 three pairs of salivary glands (the parotids, the submaxil- 
 laries, and the sub-linguals) (fig. 32), and of the mucus 
 secreted by numerous small glands beneath the lining 
 of the cheeks, gums, and tongue, called buccal glands. 
 The salivary glands belong to the class of what are called 
 rctcemose glands, consisting of numerous ducts which divide 
 and subdivide until they become ex- 
 tremely small. At the extremities of 
 the ducts there are a series of little 
 pouches or follicles, lined by the cells 
 which secrete from the blood materials 
 which the cells manufacture into saliva 
 (fig. 33). Certain nerve fibres ter- 
 minate in the cells, or send fine ^'S- 87.— Nerves ter- 
 filaments amongst them (fig. 87). The "1'"^';"^. '" ^ "l"''"'^ 
 
 ° ^ ' . of Cells in a salivary 
 
 common jam^a formed by the combined aiand : 
 
 secretion of these various secreting a, nerve: *, *, i, ceils ,- c, 
 
 organs is a colourless, slightly turbid, ""<=■="= '■ ''< ™='" ^'»'^"- 
 
 .... , - 1 rt • 1 iiigsor nerve tubes. < 
 
 Viscid, inodorous, and tasteless fluid. 
 In the normal state its reaction is alkaline. Saliva does 
 not contain more than five or six parts of solid constituents 
 to 995 or 994 parts of water. The saliva formed by the 
 sub-lingual gland is richest in sohds (2-75 per cent). 
 Submaxillary saliva contains about 2-2 per cent, and 
 parotid saliva only -4 per cent The substances in saliva 
 are mucin (as in mucus), ptyalin (the enzyme), a globulin 
 proteid, sulphocyanide of potassium, common salt (sodium 
 chloride), and traces of sodium carbonate, calcium phos- 
 phate, &c. The daily quantity of saliva secreted by an 
 
128 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 adult man is estimated at about 48 ounces, but the activity 
 of the salivary glands is dependent upon various influences 
 and conditions. Thus, movement of the lower jaw, as in 
 masticating, speaking, or singing, increases the secretion 
 — acrid and aromatic substances and hard dry food also 
 increase it. It is also under the influence of mental 
 states, emotions, and desires, through the nervous system, 
 for the sight of a feast or tempting dish may make one's 
 ' mouth water,' while fear is known to parch the mouth. 
 
 The uses of the saliva in reference to digestion are partly 
 mechanical and partly chemical. The chemical use of the 
 saliva is, by the action of its enzyme, ptyalin, to convert the 
 starchy portions of the food into a form of sugar (maltose), 
 and thus to promote its absorption. It also moistens the 
 mouth, and so assists in speech and swallowing. The 
 public speaker cannot articulate when his mouth becomes 
 dry, and we cannot swallow a perfectly dry powder. When 
 saliva is swallowed with starchy food, the action goes on for 
 15 to 25 minutes, nnt'd free acid appears in the contents of 
 the stomach. An acid (hydrochloric) is poured into the 
 stomach at the beginning of digestion in that organ, but the 
 acid first formed combines with proteids of the food. After 
 these compounds have been formed, free acid persists, 
 and immediately destroys ptyalin, arresting any further 
 conversion of starch into maltose. 
 
 Questions. 
 
 134. Enumerate the teeth in the jaw of an adult man. Make a 
 
 drawing of a tooth, showing the position of the tissues of which 
 it is composed. 
 
 135. Describe the position of the glands that secrete saKva. What is 
 
 the chemical composition of mixed saliva ? What are the uses 
 of saliva ? 
 
 136. Deglutition. — Deglutition is the act by which 
 the food is transferred from the mouth to the stomach. 
 
THE ALIMENTARY SYSTEM. 129 
 
 The mouth leads into a cavity called the pharynx (see figs. 
 31 and 34). Between it and the mouth is the soft palate, 
 which is a movable muscular partition that separates the 
 two cavities during mastication. As soon, however, as the 
 latter act is accomplished, and the bolus is pressed back- 
 wards by the tongue, the soft palate is drawn upwards and 
 backwards, so as to prevent the food passing into the nose. 
 The vocal cords (see Voice) are brought close together, 
 and the opening of the windpipe is closed by a lid called 
 the epiglottis. The bolus or pellet of food having arrived 
 near the oesophagus or gullet (which is continuous inferiorly 
 and posteriorly with the pharynx), is driven into it by the 
 action of certain muscles, which almost surround the 
 pharynx, and are termed its constrictor muscles. All 
 voluntary action ceases as soon as the food is pressed 
 backwards by the tongue into the pharynx. It is im- 
 possible to recall the pellet, and it is carried on (even 
 without our cognisance) into the stomach. This involun- 
 tary mechanism is called a reflex action. All reflex 
 mechanisms require a stimulus to call the parts into 
 action. The stimulus in this case is the contact of the 
 food with the back of the tongue and throat. The 
 reader will find that he cannot perform the action of 
 swallowing if nothing, not even saliva, is in his mouth. 
 
 The food is carried down the oesophagus or gullet to 
 the stomach by a peculiar vermicular contraction of the 
 muscular fibres of the former, well seen when a horse is 
 drinking water. This kind of movement is called a 
 peristaltic action. 
 
 137. Digestion in the Stomach. — The whole of the 
 alimentary canal below the diaphragm, or muscular parti- 
 tion which separates the cavity of the chest from that of 
 the abdomen or belly (fig. 29, O, p. 36), possesses tlie 
 following points in common, in relation to structure. The 
 stomach, the small intestine, and the large intestine, are 
 
 I 
 
130 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 all lined by mucous membrane, have a muscular coat of 
 involuntary muscular fibres, consisting of two sets of 
 fibres — namely, circular fibres internally, which surround 
 the tube or viscus after the manner of a series of rings, 
 and longitudinal fibres externally, running in the same 
 direction as the intestine itself — and are invested with a 
 smooth, glSssy, serous membrane, which, while it retains 
 the viscera in their proper position, also permits their 
 necessary movements with a minimum of friction. 
 
 The human stomach is an elongated curved pouch (fig. 
 35, p. 44), lying immediately below the diaphragm. It 
 is very dilatable and contractile, and its function is to 
 retain the food until it is duly acted upon and dissolved 
 by the gastric juice, which is secreted by glands lying in 
 its inner coat, and then to transmit it, in a semi-fluid 
 state, into the first part of the small intestine, called the 
 duodenum. Its average capacity is about five pints. 
 
 138. The -Mucous Membrane of Stomach. — The 
 mucous membrane, or lining coat of the stomach, is thick 
 and soft, and lies in irregular folds, in consequence of the 
 contraction of the muscular coat, unless when the organ 
 is distended with food. On opening the stomach, and 
 stretching it so as to remove the appearance of folds, we 
 perceive numerous very shallow pits or depressions. The 
 rest of the thickness is chiefly made up of minute tubes 
 (fig. 88), running vertically towards the surface of the 
 stomach, and secreting the gastric juice from the blood 
 in the capillaries or minute blood-vessels which abound in 
 the mucous membrane. These tubes are lined throughout 
 with columnar epithelial cells. Near the cardiac end of the 
 stomach, the gastric glands show two kinds of secreting 
 cells : (i) the gland is lined by columnar epithelial cells, 
 called the central or principal cells ; and (2) outside of 
 these, bulging from the wall of the gland, we find large 
 granular cells, caWtd parietal cells (fig. 88, B). The glands 
 
THE ALIMENTARY SYSTEM. 
 
 131 
 
 near the pylorus have only principal cells (fig. 88, A; 
 see description of fig.). It is supposed that the central 
 cells secrete pepsin, while the parietal form hydrochloric 
 acid. The zymogen in the peptic cells is called pepsinogen. 
 Pepsin is different from the enzyme that curdles milk, 
 known as the milk-curdling ferment. Pepsin differs from 
 all other enzymes in acting 
 only in an acid medium. 
 
 139. Changes in 
 Stomach. — When food 
 is introduced into the 
 stomach, -it is subjected 
 to three actions — first, to 
 heat, the temperature of 
 the stomach being, during 
 digestion, about 99° F. ; 
 second, to a slow move- 
 ment round and round, so 
 as to bring the food into 
 contact with the lining; 
 and, third, to the chemical 
 action of a special fluid 
 — the gastric juice. 
 
 The food, on entering 
 the stomach, first passes 
 into the cardiac end, thence along the greater curvature 
 from left to right to the pyloric end, and from thence 
 along the lesser curvature from right to left. 
 
 140. The changes in the mucous membrane are ; The 
 inner surface of the healthy fasting stomach is of a paler 
 pink than after the introduction of food, which causes the 
 exudation of a pure, colourless, viscid fluid, having a well- 
 marked acid reaction. This fluid, which is the gastric 
 juice, collects in drops, which trickle down the walls, and 
 mix with the food. Its two essential elements are : (1) a 
 
 Fig! 88.— Gastric Glands : 
 
 A, from pyloric end of stomach : cz, clear 
 columnar cells of month of gland ; 3, end 
 of gland, with more granular cells. B, 
 from cardiac end ; /i, principal cells ; h, b, 
 parietal cells ; c', mouth of cardiac gland. 
 C, transverse section of gland. 
 
132 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 free acid, which is usually hydrochloric alone, and occa- 
 sionally a mixture of hydrochloric and lactic acids ; and. 
 (2) an enzyme called /^««. 
 
 141. Chemical Nature of Gastric Juice. — The 
 gastric juice is highly acid, from the presence of free hydro- 
 chloric acid. The formation of free acid, from the blood 
 and lymph bathing the parietal cells, both of which fluids 
 are alkaline, may be accounted for by the interaction of 
 chloride of calcium with the hydrogen-sodium-phosphate 
 of the blood. The result of the action is phosphate of 
 calcium, sodium chloride, a,r>.A free hydrochloric acid. One 
 hundred parts of gastric juice collected from the human 
 stomach gave, of water, 99-44, organic matter, chiefly 
 pepsin, -32, of hydrochloric acid, -02, and very small quan- 
 tities of various salts, chiefly common salt. The gastric 
 juice of the dog is richer in all its constituents, containing 
 1-7 per cent, of pepsin and -3 of hydrochloric acid. Prob- 
 ably the average amount of hydrochloric acid is • 2 per cent. 
 
 142. Action of Gastric Juice. — The uses of this 
 fluid are not only to dissolve but also to modify the nitro- 
 genous elements of the food (such as albumin, fibrin, 
 casein, and, in short, all animal food except fat), converting 
 them into new substances, termed peptones, which, although 
 they coincide in their chemical coriiposition, and in many 
 of their physical properties, with the substances from which 
 they are derived, differ essentially from them in their more 
 ready solubility in water, in their power of rapidly dialysing, 
 or passing through animal membranes, as well as in various 
 chemical relations. The formation of peptone is one of 
 hydration ; that is to say, the proteid is caused to take up 
 water. Peptones are not at once formed ; intermediate 
 bodies called proteoses being produced, and there is also 
 the formation of a body called acid-albumin or syntonin. 
 All peptones are more soluble and diffusible substances 
 than the proteids, from which they were formed. 
 
THE ALIMENTARY SYSTEM. 1 33 
 
 The gastric juice exerts no action on the fats and the 
 carbo-hydrates (sugar, starch) (see p. 57). If the fats are 
 in animal cells, the walls of which are formed of albumin, 
 the walls are dissolved, and the contents set free. The 
 cellulose walls of vegetable cells are usually unaffected. 
 
 143. Case of Alexis St Martin. — The process of 
 gastric digestion was studied in 1838 by Dr Beaumont and 
 others in the remarkable case of Alexis St Martin, a man 
 who had a gunshot injury in 1822, which left a permanent 
 opening through the abdominal wall into his stomach, 
 guarded by a little valve of mucous membrane. Through 
 this opening, the mucous membrane could be seen, the 
 temperature ascertained, and numerous experiments made 
 as to the digestibility of various kinds of food. 
 
 144. Absorption in the Stomach. — What becomes 
 of the matters that are thoroughly dissolved in the stomach? 
 The albuminates, &c. which are converted into peptones, 
 are for the most part taken up by the blood-vessels of the 
 stomach, and by another set of vessels in the bowel, called 
 the ladeals. At the moment of their absorption, however, 
 peptones are converted into serum-albumin, the chief 
 proteid of the blood, by the action of the living cells in 
 and on the walls of the stomach and the coats of the 
 vessels. The rapidity with which aqueous solutions of 
 iodide of potassium, the alkaline carbonates, lactates, 
 citrates, &c. pass into the blood, and thence into the urine, 
 saliva, &c. shows that the absorption of fluids must take 
 place very shortly after they are swallowed ; and there is 
 little doubt that the blood-vessels (capillaries) of the 
 stomach constitute the principal channel through which 
 fluids pass out of the intestinal tract into the blood. 
 
 145. Time required for Digestion. — There can be 
 no doubt that the stomach is admirably adapted for the 
 digestion of the food introduced into it, because it has been 
 shown by numerous experiments that digestion will go on 
 
134 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 in gastric juice out of the stomach, but that it requires 
 three or four times longer ^a period than when performed 
 by the stomach itself. In the stomach, in most individuals, 
 rice and tripe are digested in one hour ; eggs, salmon, and 
 venison in one and a half hours ; tapioca, liver, and fish in 
 two hours ; lamb, pork, and turkey in two and a half hours ; 
 beef, mutton, and fowl in three and a half hours ; and veal 
 in four hours. There are, however, considerable differ- 
 ences in various individuals, or even in the same individual 
 at different times. 
 
 146. Conditions favourable for Good Digestion.— 
 These are : (i) a temperature in the stomach itself of about 
 99° to 100° F. ; (2) constant movement of the walls of the 
 stomach, so as to bring the food thoroughly into contact with 
 the mucous membrane and gastric juice ; (3) the removal from 
 time to time of such portions as have been fully digested ; (4) 
 a state of softness and minute division of the food ; (j) the 
 quantity of food taken — the stomach should be moderately 
 filled, but not distended ; (6) the time which has elapsed since 
 the last meal, which should always be long enough for the food 
 of one meal to have completely left the stomach before another 
 meal is introduced ; (7) the amount of exercise previous and 
 subsequent to a meal, gentle exercise being favourable, while 
 over-exertion is injurious; (8) the state of the mind, tranquillity 
 of temper favouring good digestion ; (9) the general state of 
 the bodily health, the stomach of an invalid not being usually 
 so fit for digestion as that of a person in robust health ; and 
 (10) the period of life, digestion being more active in the young 
 than in the old. 
 
 Questions. 
 
 136. Describe the process of swallowing. 
 
 138. Describe the parts seen in a section through the coats of the 
 stomach. 
 
 140. What is the appearance of the lining membrane of the stomach 
 
 before and after taking food ? 
 
 141. What are the constituents of the gastric juice ? 
 
 146. What are the conditions favourable to healthy gastric digestion? 
 
THE ALIMENTARY SYSTEM. 
 
 135 
 
 147. Digestion in the Bowels. — After the food, by 
 digestion in the stomach, has been converted into a semi- 
 fluid mass called the chyme, it passes into the intestine 
 
 Fig. 90.— Dia- 
 grammatic View 
 of the upper part 
 of a Villus: 
 
 a, a, columnar epith- 
 elium ; e, goblet ce\\ ; 
 b, 6, artery and 
 vein; c, nuclei of 
 connective tissue ; 
 d, commencement of 
 lacteal. 
 
 Fig. 89.— Section through the Walls of the 
 Small Intestine : 
 a, villus with columnar epithelium ; b, connective tissue 
 forming substance of villus ; c, blood-vessels ; d^ villus 
 showing ends of the epithelial cells ; e, Lieberkuhnian 
 gland : /, the same : g, muscularis mucosae (two layers 
 of muscular film) ; h, lacteals, one running up centre of 
 villus in submucous coat ; z, internal circular muscular 
 coat ; kj external muscular coat ; serous coat below k. 
 
 (see p. 44). The human intestine consists of a convoluted 
 tube, which, from a great change in calibre in two different 
 parts, is divided into (i) the small intestine, and (2) the great 
 intestine (figs. 29 and 34). The small intestine is about 
 twenty feet in length, and is divided by anatomists into 
 three portions — the duodenum, jejunum, and ileum, the last 
 
136 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 opening into the great intestine. The whole of this tube 
 is connected with the back of the abdonninal cavity by a 
 thin web, called the mesentery, on which blood-vessels, 
 nerves, and absorptive vessels, the lacteals, ramify before 
 penetrating into and supplying the bowel (see fig. 94, 
 
 P- 143)- 
 
 148. Microscopical Structure of Mucous Mem- 
 brane. — -When the small intestine is slit open, it presents 
 a large number of transverse folds, called valvula 
 conniventes (fig. 91), which are simply 
 doublings of the mucous membrane, so as 
 in little space to increase the surface for 
 absorption. . It has also a peculiar velvety 
 appearance, which is due to the fact that it 
 is covered over by innumerable small pro- 
 jections termed villi (fig. 89). They are 
 more numerous in the upper than in the 
 lower portions of the bowel. When 
 examined by the microscope, they are 
 found to be prolongations of the mucous 
 Fig. 91.— Small membrane, shaped like the finger of a 
 
 Intestine dis- , j 1. • j u 1 r 
 
 J , , glove, and each is covered by a layer ot 
 
 hardened by epithelial cells (fig. 90). Of these there 
 alcohol, and are two kinds : (i) the columnar epithelial 
 laid open to cell (fig. 90, a, a), and (2) a peculiar cell, 
 show the val- ^^^ ^^ ^^^^ mouth, called a goMet cell 
 (fig. 90, e). In the centre we find the 
 commencement of the true absorbent ves- 
 sel, the lacteal (fig. 90, d), and surrounding it a net- 
 work of vessels of very minute size. The villi in the small 
 intestine are to a certain extent comparable to the delicate 
 rootlets of a plant. The latter absorb moisture and 
 soluble nutriment from the soil, while the former are 
 bathed in a nutritious fluid, the chyme, and absorb readily 
 fluids by the blood-vessels, and fatty matters by the 
 
THE ALIMENTARY SYSTEM. I37 
 
 lacteals. We find also in the mucous membrane large 
 numbers of minute tubular glands, called Lieberkuhnian 
 glands, after the anatomist Lieberkiihn, who first described 
 them (fig. 89, e). In the upper part of the duodenum 
 there are a few racemose glands, like small clusters of 
 gfapes, known as Brunner's glands. 
 
 The great intestine, about five or six feet in length, is so 
 termed because it is so much wider than the smaller 
 one. It is also divided into three parts : the cacuni, which 
 is a wide pouch, often of great size in herbivorous animals, 
 and into which the 
 small intestine opens, A 
 the entrance being 
 guarded by a valve (fig. 
 36) ; the colon, which 
 forms the greater part 
 of the large intestine ; 
 and the rectum, which 
 is situated entirely in 
 the pelvis, and termin- 
 ates in the anus («ee p. 
 4S). The great resem- 
 bles the small intestine 
 in general respects, 
 but the mucous mem- 
 brane shows no villi. 
 
 149. Functions of Villi. — The function of the villi 
 is mainly the absorption of fatty matters, (i) The villi 
 exist only in the small intestine where the absorption of 
 fat goes on. (2) They are turgid, enlarged, and opaque 
 during the process of digestion and absorption, and small 
 and shrunken in animals that have been kept fasting 
 for some time before death. 
 
 150. Functions of Muscular Coat. — The small in- 
 testine has an internal circular and an external longi- 
 
 Fig. 92. 
 
 A, Coats of Small Intestine, much reduced in size : 
 a, mucous; b, muscular; c, serous. B, Small 
 Intestine, opened to show fold of mucous mem- 
 brane : rf, Peyer's patch. 
 
138 ELEMENTARY HUMAN PHYSIOLOGy. 
 
 tudinal coat of unstrlated muscle, the function of which is 
 to propel the food along the bowel. This is accomplished 
 by alternate contractions and relaxations, and thus a wave- 
 like motion is produced. This motion may be readily seen 
 in the intestines of an animal recently killed, and is termed 
 &. peristaltic action (fig. 92). 
 
 151. Action of Fluids in Small Intestine. — When 
 the food, reduced to a pulpy mass in the stomach, termed 
 chyme, passes into the duodenum, it is mixed with 
 three fluids — the bile, the pancreatic juice, and the intestinal 
 juice. 
 
 152. — Function of the Bile in Digestion. — The bUe 
 
 Fig. 93. — The under surface of the Stomach and Liver, which are 
 
 raised to show the Duodenum and Pancreas : 
 
 si, stomach ; >, its pyloric end; i, liver : g, gall-bladder; d, duodenum, extending 
 
 from the pyloric end of the stomach to the front, where the superior mesenteric 
 
 artery (jm) crosses the intestines ; pa, pancreas ; sp, spleen ; a, abdominal aorta. 
 
 is an alkaline fluid secreted by the liver (the structure of 
 which will be described in connection with the subject 
 of excretion, with which it has chiefly to do), and, after 
 having been collected in the gall-bladder (fig. 93, g), finds 
 its way into the upper part of the small intestine by a duct, 
 which usually unites with that of the pancreas, pa, and 
 opens by a common orifice. As it flows from the liver, 
 the bile is a thin greenish-yellow fluid, sometimes olive- 
 brown ; but when acted on by the gastric juice, it acquires 
 
THE ALIMENTARY SYSTEM. I39 
 
 a distinctly yellow or green hue, hence the appearance of 
 vomited bile. Its main use seems to be (i) to promote the 
 digestion of fatty matters, and it accomplishes this end by 
 a physical action both on the fats and on the intestinal 
 walls, disintegrating the former, and impressing on the 
 latter (by moistening the villi) a peculiar condition which 
 facilitates the absorption of fatty matters. (2) The bile 
 separates nutritious matters from those which are non- 
 nutritious, while it (3) stimulates the muscular movements 
 of the bowels, and (4) arrests putrefaction in the faeces. 
 
 153. Chemical Nature of the Bile. — The constit- 
 uents of the bile are the bile-salts, glycocholate and tauro- 
 cholate of soda ; the bile-pigments, bilirubin and biliverdin ; 
 a mucus-like substance, one of the nudeo albumins ; and small 
 amounts of cholesterin, soaps, fats, urea, lecithin, and 
 salts — chiefly chloride of sodium and phosphates of iron 
 and calcium. It is neutral, or alkaline, in reaction, and has 
 a specific gravity of about 1030. The amount of solid 
 matter is from 9 to 14 per cent. In human bile, by far 
 the most abundant constituent is glycocholate of soda. 
 The chief difference between the two bile-salts is that 
 taurocholate of soda contains sulphur, while the other does 
 not. Cholesterin, a substance forming the chief constit- 
 uent of gall-stones, exists only in minute quantities. The 
 fate of the biliary constituents will be considered in treating 
 of the liver. 
 
 154. The Pancreatic Juice in Digestion. — The 
 pancreatic juice is secreted by a long, narrow, flattened 
 gland called the pancreas, or sweetbread, which lies deeply 
 in the cavity of the abdomen, immediately behind the 
 stomach (figs. 37 and 93). It is a lobulated or racemose 
 gland, consisting of an immense number of small pouches 
 grouped round the extremities of small ducts. These ducts 
 unite with others, becoming larger and larger, until the great 
 duct of the gland is formed. The secretion is a colourless. 
 
14° ELEMENTARY HUMAN PHYSIOLOGY. 
 
 clear, somewhat viscid, and ropy fluid, devoid of any special 
 odour, and exhibiting an alkaline reaction. The functions 
 of the pancreatic juice are (i) to emulsionise the fat of the 
 chyme, and thus promote its absorption. If the duct of the 
 pancreas be tied, and fat be taken as food, a large amount 
 of it will appear in the faeces ; and the same result has 
 been seen in the human being in cases of diseased pancreas. 
 The juice appears not onA^ physically to emulsionise the 
 fats, but chemically to split them up into glycerin and a fatty 
 acid (p. 58). (2) The pancreatic juice also converts any 
 starchy matter, which may have escaped the action of the 
 saliva, into grape-sugar. (3) It acts partially on the 
 albuminous matters, splitting up the peptones into simpler 
 bodies, such as leucin and tyrosin. 
 
 155. Chemical Nature of the Pancreatic Juice. — 
 An analysis of human pancreatic juice showed it to con- 
 tain : water, 97-6 per cent; organic solids, i-8 per cent; 
 and inorganic salts, -6 per cent. From its peculiar action, 
 it has been assumed that four enzymes exist : (1) trypsin, 
 an enzyme that decomposes proteids; (2) amylopsin, the 
 enzyme acting on starch ; (3) steapsin, an enzyme having an 
 action specially on fats ; and (4) a milk-curdling enzyme. 
 These bodies have never been isolated. In addition, the 
 pancreatic fluid always contains some proteid matter, and 
 traces of leucin, tyrosin, xanthin, and soaps. Chloride of 
 sodium is abundant, and there are traces of phosphates 
 and carbonates, both of which cause the. alkalinity of the 
 fluid. 
 
 156. The Intestinal Juice in Digestion.— Of the 
 last of the fluids poured into the intestine, the intestinal 
 juice, we know little. It is the aggregate secretion of the 
 various glands which occur in the walls of the smaller 
 intestines. It is a colourless, or sometimes yellowish, ropy, 
 viscid fluid, which is invariably alkaline. It seems to unite 
 in itself the leading properties of the pancreatic and gastric 
 
THE ALIMENTARY SYSTEM. I4I 
 
 juices — that is to say, it resembles the former in converting 
 starch into sugar, and the latter, in converting albuminous 
 bodies into peptones. The most important action of 
 intestinal juice is that it converts cane-sugar or saccharose 
 and maltose into glucose or grape-sugar, due to an enzyme 
 called invertin. Thus all the starch and all cane-sugar is 
 exchanged into glucose before absorption. 
 
 157. Action of Minute Organisms in Intestinal 
 Canal. — -The contents of the stomach and of the first part 
 of the small intestine are acid, but they gradually become 
 neutral, and then alkaline by admixture with the bile and 
 pancreatic fluid, both of which are feebly alkaline. Such a 
 medium is one in which numerous minute organisms of the 
 nature of the lowest class of fungi, known as bacteria, live 
 and grow, and accordingly we find these lowly organisms 
 present in enormous numbers in the bowel. There can 
 be no doubt these set up chemical actions independently 
 of the enzymes we have considered. Thus they set up the 
 lactic acid change, by which the sugar in milk is changed 
 into lactic acid ; this lactic acid they further decompose 
 into butyric acid, carbonic acid, and hydrogen ; cellulose, 
 found in the cells of vegetable matter, they convert into 
 marsh gas and carbonic acid, the two chief gases found in 
 the intestine. The bacteria also act on fats, liberating 
 fatty acids, and causing the matter in the lower part of 
 the intestine to become acid. Lastly, they act on proteids, 
 giving rise to substances known as indol, skatol, and phenol, 
 which give the bad odour to the faeces. 
 
 158. Changes in the Great Intestine. — The line 
 of demarcation between the small and large intestine is 
 very obvious, and by the peculiar arrangement of the ileo- 
 ccecal valve, which guards the entrance of the small into the 
 great intestine, matters are allowed to pass forward with 
 facility, while regurgitation is impossible (see fig. 36, 
 p. 45). Structurally, the great intestine has no villi, and is 
 
142 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 more capacious, though much shorter, than the small 
 intestine. Its contents differ very materially from those 
 which are found in the small intestine, and constitute the 
 fceces. They are more solid and homogeneous, and are 
 often moulded into a definite shape. The only essential 
 change which the matters in the great intestine undergo in 
 this part of their course is, that they increase as they pass 
 onward in solidity, in consequence of the absorption of 
 fluid from them by the vessels of the mucous membrane. 
 They are propelled onwards into the rectum by the peri 
 staltic action which has been already described, and are at 
 last expelled by a partly voluntary and partly reflex effort. 
 
 The faeces consist chiefly of undigested materials (such as 
 vegetable cellular tissue, fragments of tendon, skin, and 
 disintegrated muscular fibre), but also of material derived 
 from the mucous membrane of the great intestine. It is 
 in the great intestine the chyme first acquires a faecal 
 odour, said to be due chiefly to the decomposition of 
 albuminous matters, which increases in intensity as the 
 material passes along the bowel. 
 
 The colour of the faeces varies with the food. With a mixed 
 diet, they are of yellowish-brown tint ; on a flesh diet, much 
 darker ; and on a milk diet, yellow. Their reaction is usually 
 alkaline. About four and a half ounces in ordinary circum- 
 stances are voided daily. 
 
 Questions. 
 
 147. Describe shortly the anatomical parts of the small intestine. 
 
 What is the mesentery ? 
 
 148. Describe the structure of a villus. 
 
 150. How are matters propelled along the bowels ? 
 
 152, 153. What are the chief matters in bile? 
 
 154. What is the structure of the pancreas? Where do the bile and 
 pancreatic fluid enter the bowel ? What is the action of pan- 
 creatic juice on food stufTs ? 
 
 158. How does the great differ from the small intestine ? What matters 
 are voided as faeces ? 
 
143 
 
 CHAPTER IV. 
 
 ABSORPTION OF NUTRITIOUS MATTER. 
 
 159. General. — As the chyme is propelled along the 
 alimentary canal, the watery portion, holding various 
 substances in solution, is absorbed by the blood-vessels, 
 while the fatty matter is taken up by the lacteals. It is 
 
 believed that absorp- 
 tion, so far as the 
 blood-vessels are con- 
 cerned, is partly a 
 physical process de- 
 pendent on osmotic 
 action, and partly a 
 vital process due to 
 
 —d 
 
 Fig. 94. — Lacteals from Intestine, 
 
 running in the Mesentery : 
 
 a, thoracic duct ; 3, aorta ; c, lymphatic glands ; 
 
 d. intestine. 
 
 Fig. 95. 
 Drop of Chyle : 
 On the left, corpuscles 
 lying amongst molec- 
 ular matter ; on the 
 right, corpuscles al- 
 tered by the addition 
 of acetic acid. 
 
 the selective action of the living epithelial cells clothing 
 the surface of the mucous membrane. The absorption 
 of fatty matter depends on the activity of the epithelial 
 cells covering the villi. The whole of the nutritive 
 material thus separates itself into two parts : one which 
 passes directly into the blood, and the other which enters 
 
144 ELEMKNTARY HUMAN PHYSIOLOGY. 
 
 the lacteals, and in these becomes a milky fluid called the 
 chyle. It is important to remember that all the blood 
 circulating in the digestive organs, and taking up soluble 
 nutritive matters, must pass through the liver before 
 
 Fig. 96. — ^The Absorbent System of Man : 
 
 u, junction of thoracic duct with left subclavian vein ; b^ thoracic duct ; Cy recep- 
 
 taculum chyli ; d^ portion of intestine ; f, lacteals. 
 
 entering the general circulation, and from it the cells of the 
 liver select and elaborate their secretion. But the chyle 
 passes into the blood indirectly. It is first conveyed to 
 numerous glands in the neighbourhood of the intestines, 
 
SANGUIFICATION. I45 
 
 called mesenteric glands (see Sanguification) (fig. 98). 
 Before entering these glands it is a milky fluid, essentially 
 molecular; but after it has passed through the glands it is 
 found to contain small granular cells, similar to colour- 
 less blood-cells, termed chyle-corpuscles, along with much 
 molecular matter, known as the molecular basis of the 
 chyle (fig. 95). Before passing through the glands, the 
 chyle does not coagulate on heating, but after doing so it 
 coagulates readily. The lacteal vessels proceeding from 
 these glands unite with corresponding sets of vessels from 
 the lower limbs, called lymphatics, in a wide cavity opposite 
 the last dorsal vertebra, the receptaculum chyli (see fig. 96). 
 From this cavity a duct, the thoracic duct, ascends through 
 the thorax, receives branches from the left arm and left 
 side of the head, and unites with the venous system at the 
 root of the neck on the left side, the point of junction 
 being where the left internal jugular vein unites with the 
 great vein of the left arm, the left subclavian. The 
 lymphatics of the rest of the body unite to form the right 
 lymphatic duct, which joins the venous system at a corre- 
 sponding point on the opposite side of the root of the 
 neck. The whole of the chyle, therefore, passes into the 
 blood at the root of the neck. 
 
 Question. 
 
 159. What is the distinction between chyme and chyle? Where is 
 chyle found ? Where does chyle enter the blood ? Trace the 
 course of the thoracic duct. 
 
 CHAPTER V. 
 
 SANG U I PICA TION. 
 
 160. General. — By this term we mean the making of 
 blood. In the lowest animals, such as in the amoeba, we 
 find no circulating nutritious fluid. When we ascend 
 
 J 
 
146 
 
 ELEMENTARY HUMAN PHVSIOLOGY. 
 
 higher in the scale, we find a colourless fluid containing 
 molecules made to move in certain definite directions by the 
 action of cilia in the general cavity of the body, as in a 
 sea-anemone. Still higher we meet with a colourless fluid 
 circulating in vessels, frequently communicating with the 
 body-cavity, and propelled by a special contractile organ, 
 as in the sea-urchin or ascidian ; and at last we meet with 
 a coloured fluid, circulating in vessels separate from the 
 body-cavity, and having a propelling 
 organ, or heart, of more or less com- 
 plex structure, as ifi all the vertebrata. 
 161. Sources of the Blood. — 
 The blood, in the higher animals and 
 in man, is derived from five sources : 
 (i) from materials, mostly of the 
 nature of fats, absorbed by the lac- 
 teals in the primary digestion of the 
 food in the alimentary canal {chyle) ; 
 (2) from soluble matters, such as 
 water, soluble mineral matters, sugar, 
 and proteids derived from peptones 
 absorbed by the blood-vessels, and 
 first of all sent through the liver ; (3) 
 from cells formed in certain glands 
 called blood-glaiids, found in various 
 parts of the body ; (4) from materials 
 Fig. 97.— General View re-introduced into the blood from the 
 of the Anatomy of a tissues — products of the -decomposi- 
 Lymphatic Gland : ^^^^ ^^^ solution of portions of these 
 
 The arrows indicate the direc- . ^ - •. ^ 
 
 tionofflowofiymph. tissucs Consequent on their vital ac- 
 re, body of gland ; I, lym- tivity (lymph) ; and (s) from a small 
 phatic entering gland. amount of matter which may be 
 
 absorbed by the skin. 
 
 162. The Blood-glands. — The so-called blood-glands 
 are — the spl'ee7i, a large organ found almost in juxta- 
 
SANGUIFICATION. 1 47 
 
 position with the left end of the stomach ; the suprarenal 
 capsules, two organs found in the lumbar region, one on 
 the top of each kidney ; the thymus, a gland found in the 
 thorax, immediately behind the breast-bone, of larger size 
 before birth and during the earlier years of life than during 
 adult life ; the thyroid, a gland existing in front of the box 
 of the larynx ; the glands of Peyer, in the mucous membrane 
 of the small intestine ; and lastly, the lymphatic glands, 
 which we find in many parts of the body, such as in the 
 
 Fig. 98. — Section of a Lymphatic Gland: 
 
 ^, strong fibrous capsule sending partitions into the gland ; b, partitions between 
 the fotlicles or pouches of the cortical or outer portion ; c, oartitions of the 
 medullary or central portion ; rf, f, masses of retiform tissue filled with white 
 cells in the pouches of the gland ; /, lymph-vessels which bring iymph to the 
 gland, passing into its centre ; g^ confluence of those leading to the efferent vessel, 
 k, which carries the lymph vcw&y/rojn the gland. 
 
 groin, the armpit, and the neck. The structure of a lym- 
 phatic gland will be understood from the description of 
 fig. 98. All of these glands agree in certain points of their 
 anatomy : they have no ducts to carry off the secretion, 
 except we regard as such the numerous lymphatics by 
 which they are supplied ; they consist of shut sacs, con- 
 taining (except the thyroid and suprarenal capsules) a 
 tissue called adenoid or retiform tissue, in the meshes of 
 the network of which there are white blood-corpuscles; 
 
148 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 and finally, they are richly supplied with blood-vessels, 
 lymphatics, and nerves. 
 
 163. Nature of Lymph. — The various tissues of the body 
 are nourished by blood brought into close proximity to them 
 by minute vessels termed capillaries. While the blood is 
 passing through the capillaries, part of it transudes through 
 their walls to nourish the tissues, or, possibly, it is secreted 
 by living cells in the capillaries and tissues. A portion of this 
 fluid or plasma is taken up by the tissues, and the other por- 
 tion is left behind, constituting the fluid found in almost every 
 tissue, to which it owes its softness and moistness. The tissues 
 perform certain functions, and in doing so undergo disintegra- 
 tion, the materials resulting from which pass into a fluid con- 
 dition. This fluid matter resulting from the disintegration of 
 the tissues, together with the excess of nutritious fluid which 
 has transuded from the vessels, is called lymph, and is taken 
 up by the commencements of a number of minute vessels termed 
 lymphatics. The lymphatics carry the lymph to glands dis- 
 tributed here and there throughout the body, called lymphatic 
 glands, where it is acted upon in such a manner as to fit it for 
 being carried back again into the blood. Thus the lymph re- 
 sults partly from matters produced by the tear and wear of the 
 tissues, but these waste-products the bodily economy, like a 
 manufactory, uses up as far as possible. The kernels or swell- 
 ings in the armpit during a whitlow, or after poisoning, are 
 swollen lymphatic glands. The lymphatic glands of the mes- 
 entery, or web connecting the bowel with the body, elaborate 
 chyle, not lymph, and are termed mesenteric glands. In the 
 lymphatic glands, also, the lymph is brought into close rela- 
 tion with the blood, and interchanges between these fluids 
 probably take place. 
 
 164. Blood, Chyle, and Lymph contrasted.— Blood 
 and chyle have already been described. Lymph is a slightly 
 yellowish or pale fluid, having a specific gravity of about 1018. 
 It contains numerous corpuscles — lymph-corpuscles — which are 
 of the same nature as the colourless cells in the blood.. Lymph 
 is distinguished from chyle by having in it almost none of the 
 fine molecular matter present in chyle. We may compare the 
 
SANGUIFICATION. 1 49 
 
 composition of one hundred parts of each of the three fluids in 
 man, thus : 
 
 Lymph. Chyle. Blood-plasma. 
 
 Water 95.0 90-5 90-2 
 
 Solids 5.0 9'5 9.7 
 
 Fibrin o-i q.i 0.4 
 
 Albumin 4.1 7.0 7'8 
 
 Fat trace. i-o trace. 
 
 Extractives 0-3 ) 0'56 
 
 Salts o-S S ''"^ 0-85 
 
 From this table we learn (i) that chyle and lymph, especially 
 the latter, contain less proteid matter than blood ; (2) that 
 fibrin is in greatest abundance in blood ; and (3) that fat is in 
 greatest abundance in chyle. The three fluids, however, when 
 we exclude the corpuscles, bear a striking resemblance. 
 
 165. Structure of the Spleen.— This is the largest 
 and most important of the blood-glands. It is of an oblong 
 flattened form (fig. 93), soft, of very brittle consistence, 
 highly vascular, of a dark bluish-red colour, and situated 
 near the cardiac or left end of the stomach. On cutting 
 into it, a section shows the presence of fibrous bands, termed 
 trabecules, united at numerous points with one another, and 
 running in all directions. The parenchyma, or proper substance 
 of the spleen, occupies the interspaces of the above-described 
 areolar framework, and is a soft pulpy mass of a reddish-brown 
 colour, consisting of coloured and colourless blood-corpuscles 
 and protoplasmic matter. The venous blood of the spleen 
 is carried away by the splenic vein, which contributes to form 
 the great portal venous system carrying blood to the liver ; 
 while arterial blood is supplied by the splenic artery. The 
 branches of the latter subdivide and ramify like the branches 
 of a tree (fig. 99), with the Malpighian or splenic corpuscles 
 attached to them like fruit (c, c, c). These corpuscles, 
 originally discovered by Malpighi, appear in sections as 
 whitish spherical bodies filled with granular matter and many 
 nucleated cells. They are in reality elongated or somewhat 
 ejgg-shaped masses of retiform tissue surrounding or attached 
 to the wall of a blood-vessel. The spleen-pulp contains cells 
 
iS° 
 
 ELEMENTARV HUMAN PHYSIOLOGY. 
 
 of various kinds in retiform tissue (fig. 100). Many theories 
 have been advanced as to the functions of the spleen ; but 
 the one most generally adopted is, that it has to do (i) with 
 the formation of the colourless corpuscles of the blood ; and 
 
 Fig. 99. 
 
 Portion of Splenic Artery, a, ^, 3, 
 having Malpighian bodies attached, 
 
 Fig. 100. 
 
 Cells from the Spleen Pulp : 
 
 ', similar to a colourless corpuscle of 
 
 blood : b, nucleated cell ; r, bi-nucle- 
 
 ated cell ; dy cell containing three 
 
 cells in interior. 
 
 (2) with the destruction of effete or worn-out red corpuscles. 
 Occasionally, in spleen pulp, we meet with large cells similar 
 to d (fig. 100), inclosing two or three cells similar to blood- 
 corpuscles. It is to be noted that the spleen has been 
 successfully removed from animals without any marked dis- 
 turbance of the system. In these circumstances some of the 
 other blood-glands probably did its work. 
 
 166. The other BLOOD-GLANDS.-r-Our knowledge of the 
 functions of the other organs classed as blood-glands is still 
 uncertain. The lymphatic glands, found in many localities, 
 such as the groin and armpit ; the thymus,- a gland in the 
 thorax, behind the sternum, reaching its greatest size in very 
 early life, and gradually wasting towards adolescence ; thejf/a«flJf 
 of Peyer, in the intestinal mucous membrane ; and the red 
 marrow of bone have all to do with the productioii of blood- 
 corpuscles. The red marrow of bone, in particular, is the birth- 
 place of red corpuscles. In these organs we find adenoid (reti- 
 form) tissue, but this tissue exists in other parts of the body. 
 It exists beneath the mucous membranes, and here and 
 there it forms knots or masses, as in the tonsils, and in the 
 solitary glands of Peyer. In the meshes of this tissue we 
 
THE LIVER. 151 
 
 always find numerous white blood-corpuscles, which are 
 probably developed here. Many of these while corpuscles, 
 called leucocytes, or wandering cells (because they wander about 
 in the tissues by their amoeboid movements), are believed to 
 guard the body against the attacks of its invisible foes, bacteria, 
 bacilli, and other organisms that are injurious to the body, when 
 they obtain entrance into the tissues. The white cells destroy 
 these micro-organisms by eating them up {phagocytosis), and 
 thus a war is carried on between the white cells and these 
 minute parasites, which are mostly of the nature of fungi. 
 
 The other so-called blood-glands have functions obscurely 
 concerned in removing from the blood various waste-products. 
 These waste-products are probably decomposed into simpler 
 substances, and are then eliminated by the true organs of 
 excretion. Thus the suprarenal bodies decompose effete pig- 
 ment, and the thyroid body destroys the constituent of mucus 
 called mucin. In all likelihood, liowever, these organs have 
 other functions yet unknown. The pineal gland is an 
 abortive ancestral eye, and the pituitary body is a very much 
 altered gland, partly of nervous, partly of mucous origin. 
 
 Questions. 
 
 161. From what sources is the blood continually replenished? 
 
 162. Enumerate the blood -glands. 
 
 163. What is lymph ? Compare it with chyle and blood. 
 
 165. Describe the structure of the spleen. What functions have been 
 
 attributed to the spleen ? 
 
 166. What functions may be performed by leucocytes ? 
 
 CHAPTER VI. 
 
 THE LIVER. 
 
 \(i1. General Description. — This organ is the largest 
 and heaviest gland in the body, weighing, on an average, 
 65 ounces avoirdupois. It is situated on the right side, 
 beneath the lower ribs (fig. 29). It consists of five lobes, 
 of a dark reddish colour, and these lobes are divided into 
 
152 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 lobules. The lobules are bound together by areolar tissue, 
 and the structure of all is alike. The liver is supplied 
 with the blood from which it elaborates its secretions by the 
 portal vein (fig. 72), a vessel which collects all the blood 
 circulating in the stomach, spleen, and intestines. The 
 portal vein divides and subdivides in the liver, till it forms a 
 plexus of minute vessels between and in the lobules, from 
 which originate the radicles of the hepatic vein (fig. 72), a 
 vessel which carries the blood from the liver to the inferior 
 vena cava. The connective tissue of the liver, and its 
 vessels and nerves, are supplied by a special artery, the 
 hepatic artery (fig. 75, n). The proper secreting structure 
 of the liver consists of numerous compressed 
 cells, about the Tirjn)''^ ^^ ^'i vixi^ in dia- 
 ^i^i meter, called ;4(?^>3/«Vir,f//s- (fig. 101, ^). These 
 cells secrete materials from the blood, 
 which they elaborate into bile. This secre- 
 Fig. 101. tion passes into minute ducts, the bile- 
 Hepatic cells, * ; ducts, which originate in minute spaces, a, 
 dud «r orSn' between the cells, b. These ducts convey 
 ating amongst the bile out of the liver ; and after it has 
 them, b. become inspissated and mixed with niucus, 
 
 from small mucous glands in the larger ducts, and from 
 the gall-bladder (fig. 37, b), it is poured into the duo- 
 denum. 
 
 i68. Circulation in the Liver. — When we examine 
 a thin section of the liver, we see irregularly polygonal areas 
 more or less sharply differentiated by connective tissue. 
 These are the lobules of the liver, and they consist of 
 hepatic cells and blood-vessels. Usually slightly oval, or in 
 transverse section polygonal, the length of a lobule is j\th 
 inch, and its breadth ^th inch. Around the circumference 
 of each lobule lie the ramifications of the portal vein, called 
 the interlobular veins. Capillaries pass from these into the 
 lobule, and they unite to form a central vein (fig. 102). 
 
THE LIVER. 
 
 153 
 
 Fig. 102. — Section of Rabbit's Liver near the surface. ' Injected from 
 
 the Portal Vein. 
 Observe three lobules. The injection has filled the branches of the portal vein, 
 
 called interlobular \"eins, and in the lobule to the left it has entered the lobule 
 
 and passed on to the central vein (intralobular vein). 
 
 Fig. 103, — Section of Cat's Liver near the surface. Injected from 
 the Vena Cava. 
 
 Observe four lobules. The injection has filled the central vein and the capillaries 
 leading into it, but it has not entered the portal capillaries, or interlobular veins. 
 
154 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 These capillaries form networks with the vessels in adjoin- 
 ing lobules. The spaces in the capillary network are 
 occupied by hepatic cells,- and these are arranged in a 
 radial manner round the vessel in the centre of the lobule. 
 This central vessel is termed the intralobular vein (fig. 103). 
 The intralobular veins are the beginnings of the hepatic 
 veins. Each intralobular vein opens into a sublobular vein, 
 which runs on one side of the lobule, and by the junction 
 of the sublobular veins the hepatic veins are formed. The 
 •branches of the hepatic artery run along with those of the 
 portal vein, and terminate in the interlobular tissue, 
 where the branches of the portal vein and of the hepatic 
 veins and the bile-ducts wind round them in a spiral 
 manner. The small veins originating from the plexus 
 formed by the hepatic artery open into interlobular veins 
 of the portal system. The hepatic artery also suppHes a 
 network of fine capillaries found in the capsule of the 
 liver. The course of the blood-vessels is therefore as 
 follows : . The portal vein enters the fissure of the liver, 
 divides again and again into finer and finer branches 
 which run between the lobules {itiierlobular veins). From 
 these, small capillaries enter the lobules and terminate in 
 the central veins (intralobular veins). Several of such 
 veins form a sublobular vein, and these form the hepatic 
 vein. The capillaries of the hepatic artery terminate out- 
 side the lobules. 
 
 Unlike what we find in other glands, very few hepatic 
 cells bound the lumen of the gland, not more than two 
 being related to a single lumen or bile-capillary, and the 
 structure is complicated by the arrangement that bile- 
 capillaries do not lie on one but on several sides of a 
 hepatic cell. These form a meshwork in which the hepatic 
 cells are situated. The bile-capillaries, or beginnings of 
 the hepatic ducts, are passages among the hepatic cells. 
 Sometimes they are termed intralobular bile-passages. At 
 
THE LIVER. 155 
 
 the margins of the lobules they pass into the interlobular 
 bile-ducts, which have a distinct wall, composed of a 
 structureless basement membrane and of flat epithelial cells. 
 By the union of interlobular ducts the larger bile-ducts are 
 formed ; these have a cubical or columnar epithehum. 
 
 169. Functions of the Liver. — The more obvious 
 function of this organ is the secretion of bile, and for many 
 years this was supposed to be its sole function. Research, 
 however, has shown that the liver is the seat of very active 
 changes which are hidden from the eye, and it has also 
 been ascertained that these changes are as necessary for 
 the well-being of the body as is the secretion of bile. The 
 liver is not to be regarded, therefore, as a gland having 
 only to do with the secretion of one of the digestive fluids ; 
 indeed, as has been shown, the bile plays only a subsidiary 
 part in the digestive process. It is important to note that 
 the liver receives a large amount of blood by the portal 
 vein, and that this blood is rich in materials absorbed by 
 the capillaries of the stomach, intestines, and spleen. The 
 blood of the portal vein, therefore, during absorption 
 following the digestion of food, is not like ordinary venous 
 blood. Thus all matters absorbed from the alimentary 
 canal in the first instance pass to the liver. From this 
 blood the hepatic cells select certain materials, proteids, 
 fats, and carbo-hydrates (in the form of glucose), and 
 submit these to various processes, with the result of 
 forming other substances, some of which are thrown out 
 in the bile, while others are retained in the body for further 
 use. 
 
 170. The liver, from this point of view, has to do with 
 the following processes : (i) the formation of ^//i?; (2) the 
 formation in some circumstances ol fatty matter stored up 
 for a time in the hepatic cells ; (3) the formation from 
 glucose chiefly of a carbo-hydrate, a kind of animal starch, 
 called glycogen ; and (4) the formation of urea from various 
 
156 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 substances originally derived from proteids, traceable back 
 either to the proteids of the food or the proteids of the 
 tissues, or to both. During embryonic life the liver is also 
 the seat of the formation of blood-corpuscles. This func- 
 tion is not carried on during adult life, but it is not improb- 
 able that even then in the liver there may be the destruction 
 of effete or worn-out red blood -corpuscles, and undoubtedly 
 the liver is the seat of the decomposition of a part of the 
 worn-out haemoglobin of the red blood-corpuscles. We 
 shall very shortly discuss each of these functions. 
 
 {a) The Formation of ^//i?. a— This has been already 
 described. We would only add that bile may be regarded 
 as one of the waste-products arising from the changes 
 happening in the liver. This waste-fluid — the bile — is 
 still, however, put to subsidiary uses in the processes of 
 digestion and absorption. 
 
 (b) The Formation of Fat. — Little globules of fatty matter 
 are often found in the hepatic cells. These globules may 
 sometimes so overload the cell as to hide the nucleus, and 
 then we have a fatty liver. During starvation this fat may 
 be used up. 
 
 (1:) The Formation of Glycogen. — This undoubtedly is one 
 of the most important functions of the liver, and it is part 
 of a general process for the using up of carbo-hydrates, 
 known as glycogenesis. The glucose brought to the liver 
 from the intestinal canal is changed by the hepatic cells 
 into glycogen, a substance in many ways like ordinary 
 starch. Glycogen differs, however, in giving a reddish- 
 brown colour with iodine instead of the well-known blue 
 colour given when a solution of iodine is brought into 
 contact with starch paste or with a solution of starch. As 
 glycogen may be formed in the liver even when no carbo- 
 hydrates are taken in the food, it must be formed from 
 the proteid matter existing in the hepatic cells. The 
 glycogen may remain stored up in the hepatic cells for a 
 
THE LIVER. 157 
 
 considerable time. When an animal dies, the glycogen 
 thus stored is quickly changed into sugar, so if we make 
 an infusion of dead liver with hot water, we readily obtain 
 a solution of sugar, and not of glycogen. During life, and 
 probably in the intervals when digestion and absorption of 
 carbo-hydrate is not going on, the glycogen leaves the 
 hepatic cells and is carried by the blood-stream all through 
 the body. It thus reaches the muscles in particular, and 
 there it is changed back again into sugar, and is then used 
 up for the nutrition of the muscular tissue. Some suppose 
 that the change of glycogen into sugar occurs before the 
 glycogen leaves the liver. In this way the muscles receive 
 an ample supply of carbo-hydrate, and it is from this that 
 most of the energy of the muscle is derived. 
 
 {d) The Formation of Urea. — We have seen that the 
 proteid matter is first changed into peptone by the gastric 
 juice, or into bodies somewhat similar by the pancreatic 
 juice. These peptones are converted into serum-albumin 
 at the moment of absorption, and in this way, say after a 
 diet rich in meat, the liver cells receive a large supply of 
 proteid matter. Some of this may pass through the liver 
 unchanged, and be carried to the muscles and other tissues 
 for their nourishment. A portion, however, appears to be 
 decomposed by the hepatic cells, with the formation of 
 urea, which passes into the blood, and is there thrown 
 out by the kidneys into the urine. Thus a diet rich 
 in proteids— in other words, a flesh diet — always causes an 
 increase in the urea eliminated, whereas a diet poor in 
 proteids, as with most vegetable foods, causes a diminution 
 in the amount of urea. It is not to be supposed, however, 
 that one of the functions of the liver is to form urea when 
 we take an excess of proteid in the food. It is more 
 likely that the other portion of the proteid, the part left after 
 the urea has been removed, is of great nutritional import- 
 ance, and, as it now contains no nitrogen (all the nitrogen 
 
158 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 having gone off in the urea), it may be changed into fat or 
 glycogen. There is also evidence to show that urea may 
 be formed from leucin and tyrosin formed by pancreatic 
 digestion. These crystalline bodies are absorbed from the 
 bowel and carried to the liver, there to be submitted 
 to further chemical changes leading to the formation of 
 urea. Lastly, the liver may form urea, or other nitrogenous 
 bodies, such as uric acid, from nitrogenous bodies that 
 have come from the waste of muscular tissue. 
 
 (e) Destruction of Waste Hcemoglobin. — As already men- 
 tioned, worn-out red corpuscles are destroyed in the spleen. 
 One of the substances thus set free is the pigment hcemo- 
 globin, which is carried to the liver, there further decomposed, 
 and the refuse thrown into the bile, appearing in this fluid 
 as the bile-pigments — namely, bilirubin and biliverdin. Some 
 of the pigmentary products thus formed are carried to the 
 kidneys, and are there eliminated as the pigment of the urine, 
 urobilin, &&, and others may be deposited in the tissues. 
 
 171. Fate of the Bile Constituents. — The bile 
 passes, as has been described, into the duodenum, and 
 there it has an influence both on digestion and on absorp- 
 tion. It is not all voided in the faeces, but a portion is 
 absorbed and returns to the liver. The bile-salts, glyco- 
 cholate and taurocholate of soda, exist in the faeces only 
 to a small extent, and as much as seven-eighths of the 
 total amount are absorbed and seiit ba:ck to the liver. It 
 is likely that in the intestine they are -decomposed into 
 taurin, glycocin, and cholalic acid. Small amounts of 
 these appear in the faeces ; the remainder return to the 
 liver. Their ultimate destination is not well known, but it 
 has been stated that the glycocin is changed into urea 
 and the taurin into a body called taurocarbamic acid, 
 both of which are then eliminated by the kidneys. The 
 bile-pigment becomes stercobilin, the pigment of the faeces. 
 Finally the cholesterin and mucus pass off" in the faeces. 
 
THE RESPIRATORY SYSTEM. 
 
 159 
 
 Questions. 
 
 167, 168. Describe the minute structure of a lolnile of the hver. 
 
 168. From what sources does the hver receive blood? How does its 
 
 structure differ from that of an ordinary secreting gland ? 
 
 1 70. Enumerate the functions of the liver, (c ) How does glycogen 
 
 differ from common starch ? {d) In what ways may urea be 
 formed ? (e) What is the origin of the bile-pigments ? 
 
 171. What becomes of the chief constituents of the bile ? 
 
 C H APT ER VII. 
 
 r//£ RESPIRATORY SYSTEM. 
 
 172. General Statement. — The organs and process 
 of respiration now claim our attention. We have already 
 stated that the blood of 
 the arteries differs in 
 colour from that of the 
 veins, the former being 
 of a bright scarlet tint, 
 while the latter is pur- 
 plish in colour. The 
 arterial represents pure, 
 and the venous impure 
 blood ; the change from 
 the former to the latter 
 having taken place in 
 the capillaries, which 
 form the bond of union 
 
 between the termination _. ,„, 
 
 Fig. 104. 
 
 of an artery and the jheXungs and Heart' (viewed in front) : 
 beginning of a vein 
 (fig. 77). The chemi- 
 cal differences between 
 arterial and venous blood are slight, except in relation to 
 the gases held in solution in these fluids. The two kinds 
 
 rt, aorta : d, windpipe ; /, A, lungs : /, /', right 
 and left auricles of heart : p, right ventricle ; o^ 
 apex of left ventricle ; y, pulmonary artery. 
 
i6o 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 of oxygen, 
 
 and 
 
 of blood differ widely in this respect, there being a smaller 
 
 greater quantity of carbonic 
 acid, in venous than in 
 arterial blood. 
 
 173. The organs by which 
 the impure and dark venous 
 bipod is converted into pure, 
 bright scarlet, arterial blood, 
 are the lungs, and the agent 
 by which this change is 
 effected is the oxygen of the 
 air we breathe. In their 
 simplest form, as they occur 
 in certain reptiles, the lungs 
 are air-sacs, existing as two 
 
 Fig. 
 
 105. — Blood-capillaries of 
 Lung injected. 
 
 elastic membranous bags, having small honeycomb-like 
 depressions known as ' air-cells ' on their inner surface, 
 communicating with the external air by a tube known as 
 the windpipe or trachea, which opens through the larynx 
 or organ of voice into the throat. These bags are lined by 
 a delicate, thin, and moist mucous membrane, in which is 
 imbedded a network of capillaries, 
 through which all the blood is driven 
 by the heart (figs. 105 and 106). 
 The moist partition between the 
 blood in this network and the air in 
 the interior of'the lungs is so thin 
 as to allow an interchange between 
 the gases of the blood and the gases of the air — that is 
 to. say, oxygen passes from the air in the air-cells into 
 the blood, while carbonic acid gas passes outwards from 
 the blood into the air in the air-cells. This is a pheno- 
 menon dependent largely on the laws of diffusion and 
 admixture of gases through animal membranes, but the 
 living cells lining the air-cells take part in the process. 
 
 Fig. 106.— Network o{ 
 Capillaries of Lung. 
 
THE RESPIRATORY SYSTEM. l6l 
 
 The air of expiration, as it passes over the moist air-pas- 
 sages, becomes laden with aqueous vapour. 
 
 174. Conditions of Respiration. — In the higher ani- 
 mals and in man, these essential parts are much compli- 
 cated and modified in a variety of ways. The anatomical 
 details (figs. 29, 38, and 104) may be considered under the 
 following heads : Firstly, the lungs afford an immense 
 extent of mucous .membrane, covered by vascular network, 
 through which, as in the simpler form, the blood flows in 
 innumerable minute streamlets (fig. 105), only separated 
 by a thin membrane from the atmospheric air that has 
 been inhaled ; secondly, there is such an arrangement of 
 the circulating system, that fresh blood is perpetually 
 driven from the right side of the heart through the lungs 
 onwards to the left side of the heart ; and thirdly, 
 there are arrangements for the frequent and regular change 
 of the air contained in the lungs. 
 
 175. Special Anatomy of the Organs. — We shall first 
 consider the lungs and the passages leading to them. The 
 back of the mouth, or pharynx, is connected with the outer 
 air in two ways — namely, by the nasal passages and nos- 
 trils, and by the mouth (figs. 31 and 38). Through either 
 of these channels the air may pass to and from the lungs, 
 but the nostrils are, properly speaking, the entrances to the 
 respiratory system. Behind the root of the tongue, we 
 find a chink or aperture, the glottis, bounded laterally by 
 two folds of membrane called the vocal cords, which may be 
 more or less widely separated from each other (see Voice). 
 This aperture is guarded by a leaf-like lid, the epiglottis, 
 which can be closed when expedient, so as to prevent 
 the entrances of particles of food, drink, &c. (fig. 31). The 
 glottis opens downwards, into a box-like chamber called 
 the larynx (which is the organ of voice) ; and leading 
 downwards from the larynx runs the trachea, or windpipe, 
 a tube kept permanently open for the passage of air, by 
 
 K 
 
l62 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 cartilaginous rings that surround the anterior two-thirds 
 of it. These are united, and the back of the tube is formed, 
 by a fibrous membrane or muscle. The windpipe, which 
 is easily felt by the hand, and lies just below the projecting 
 part of the larynx, popularly known as ' Adam's apple,' is 
 about four and a half inches in length, and about three- 
 fourths of i an inch wide. Passing into the cavity of the 
 chest, it divides into two branches, which are termed the 
 right and left bronchi {iig. 104). Each bronchus enters 
 the lung of its own side, and divides into a great number 
 
 Fig. 107. Fig. 108. 
 
 Air-tube ending in Air-vesicles : Scheme of Air-vesicles : 
 
 u^ pleura. a^ blood-vessels ; b, air. 
 
 of smaller tubes, called the bronchial tubes, which again 
 go on subdividing (fig. 38). These finest tubes end in 
 elongated dilatations, the infundibula, from the walls of 
 which bulge out the air-cells, averaging ■^^\k\. of an 
 inch in diameter (figs. 107 and 108). If we can con- 
 ceive a bunch of grapes with its stem and all its minute 
 branches, and the grapes attached to the ends of these, to 
 be hollow, we get a good idea of the mode in which the 
 lung is constructed, except that it does not represent all the 
 
THE RESPIRATORY SYSTEM. 
 
 163 
 
 e&» 
 
 sacculation or partitioning of the terminal 'cells.' It is in 
 consequence of the air included in these ' cells ' that the 
 lungs have a soft spongy feeling, and crackle when com- 
 pressed between the fingers. Each lung is invested by its 
 own investing serous membrane, termed \he. pleura, which 
 serves the double purpose of facilitating the movements 
 necessary in the act of respiration, and in suspending each 
 lung in its proper position (fig. 107, a). 
 
 176. General Description of Process. — The Mood 
 is being perpetually changed, and driven in a constant 
 current through the lungs by the action of the heart, 
 the venous or impure blood being 
 collected in the right ventricle, and 
 thence conveyed by the pulmonary 
 artery into the lungs. In these, 
 again, it gives off carbonic acid and 
 aqueous vapour, and absorbs oxygen 
 (as already described) ; after these c — ;, 
 changes, it is collected, and returned 5. iVi 
 to the left auricle by four vessels 
 called the pulmonary veins (fig. 
 
 73). d 
 
 The mode in which the air is 
 renewed in the lungs next requires 
 notice. This is effected by the 
 respiratory movements, which consist 
 in alternate acts of inspiration and 
 expiration, with an intervening pause 
 before the process is renewed. An 
 adult man in a sitting position per- 
 forms the respiratory act from thir- 
 teen to fifteen times in the minute, 
 but much more rapidly if taking 
 exercise. At each inspiration, about 
 30 cubic inches of air are inspired, and at each expiration 
 
 Fig. 109.— Diagram 
 showing Changes of 
 Chest in Respiration : 
 
 rt, windpipe : i, diaphragm ; c, 
 inspiration ; d, expiration. 
 
164 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 nearly the same volume is exhaled, allowance being made 
 for temperature, which in the exhaled air may equal that of 
 the blood. From 300 to 400 cubic feet of air thus pass 
 in and out of the lungs of a man at rest in the course of 
 twenty-four hours, and these are charged with carbonic acid, 
 and deprived of oxygen to the extent of nearly 5 per cent. ; 
 or, to put it in another form, about 18 cubic feet of the one 
 gas are taken in, and of the other gas are given off. The 
 quantity of carbon thus excreted in the form of carbonic 
 
 acid gas is nearly repre- 
 sented by eight ounces of 
 pure charcoal. The amount 
 of watery vapour separated 
 by the lungs daily varies 
 from six to twenty ounces, 
 according to the diet, exer- 
 cise, temperature, humidity 
 of the air, &c. 
 
 177. Mechanism of 
 Respiration. — The chest 
 (or thorax, as it is termed 
 by anatomists, fig. 12) is 
 so constructed as to be 
 capable of enlargement in 
 height (vertically), in depth 
 (or from the front back- 
 wards), and in width (or 
 from side to side). Its 
 height is increased mainly 
 by the descent of the dia- 
 phragm (figs. 109 and 1 10), 
 and to a certain extent by 
 the elevation of the ribs. 
 
 Fig. 110.— The lower part of the 
 Thorax, opened to show the upper 
 side of the Diaphragm from be- 
 fore : 
 
 «, sixth dorsal vertebra : h^ fourth lumbar 
 vertebra ; c, ensiforni cartilage ; rf, <f-, 
 aorta ; e, oesophagus ; y", opening for in- 
 ferior vena cava, i, 2, 3, trefoil tendon ; 
 4, 3, central portions of diaphragm: 6, 
 
 right, and 7, left crus of diaphragm. 
 
 and the widening of the intercostal spaces ; while its depth 
 and width are increased by the elevation of the ribs which 
 
THE RESPIRATORY SYSTEM. l6$ 
 
 carry forward and elevate the breast-bone (or sternum), espe- 
 cially at its lower end, and which are slightly rotated on an 
 imaginary axis, joining their extremities, whereby their cen- 
 tral portion is raised, and to a small extent carried away from 
 the mesial plane of the chest It is only in forced or deep 
 inspiration that all these means of enlarging the chest are 
 called into play. An ordinary inspiration is attended in men 
 with "very slight elevation of the ribs (about one-twentieth 
 of an inch), while in adult women the elevation is greater, 
 especially in the upper ribs ; the cause of this difference in 
 the sexes probably lying in the narrower waist of the female 
 requiring a compensation in the upper part of the chest. In 
 early life, and when women are untrammelled by conven- 
 tional garments, there appears to be no difference. There are 
 three varieties of ordinary respiration, namely: (i) abdominal, 
 or that chiefly effected by the diaphragm, and seen in the 
 motion of the walls of the belly ; (2) costo-inferior, or that 
 in which the seven lower ribs are observed to act ; and 
 (3) costo-superior, or that effected in a considerable degree by 
 the upper ribs. The first variety occurs in infants up to the 
 end of the third year, and in males generally ; the second, 
 in boys after the age of three, and in men ; and the third, 
 in adult females (fig. 109). 
 
 178. Number of Respiratory Movements, &c. — Every 
 complete act of respiration is divisible into four parts — namely 
 (i) Inspiration; (2) a short pause, not always observed; (3) 
 expiration ; and (4) a considerable pause, occupying about one- 
 fifth of the whole time required for one complete respiratory 
 act. The act of expiration is always more prolonged than that 
 of inspiration, the former being to the latter in the ratio of 
 12 : 10 in adult males, and as 14 : lo in children, women, and 
 aged persons. The number of respiratory acts performed in a 
 minute varies at different ages. At birth there are 44 respira- 
 tions in one minute ; at 5 years of age, 26 ; from 15 to 20, 20 ; 
 from 20 to 25, 18 ; from 25 to 30, 16 ; from 30 to 50, 18 : so 
 that from 16 to 20 maybe taken as the ordinary range for 
 
r66 ELEMENTARY HUMAN PHVSIOLOGY. 
 
 healthy adults. The average ratio which the number of res- 
 pirations bears to the number of heart-beats in a given time is 
 about I : 4-^, and if there be any great deviation from this 
 ratio, there is probably some obstruction to the aeration of the 
 ■ blood, or some disorder of the nervous system. 
 
 179. Capacity of the Lungs. — When the lungs have 
 been emptied as much as possible of air by the most 
 powerful expiratory effort, they still contain a quantity over 
 which we have no control, and which may be estimated at 
 about 100 cubic inches. To this portion of the contents 
 of the lungs the term residual air is applied. In addition 
 to this residual air, physiologists distinguish, in connection 
 with the respiratory process, supplemental air, which is that 
 portion which remains in the chest after an ordinary gentle 
 expiration, but which may be displaced at will, 100 cubic 
 inches ; breathing or tidal air, which is the volume that 
 is displaced by constant gentle inspiration and expira- 
 tion, about 30 cubic inches ; and complemental air, or the 
 quantity which can be inhaled by the deepest possible in- 
 spiration, over and above that which is introduced in ordi- 
 nary breathing, 100 cubic inches. The greatest volume of 
 air that can be expelled by the most powerful expiration, 
 which is obviously the sum of the supplemental, tidal, and 
 complemental air, is designated as the vital capacity — in allj 
 230 cubic inches. 
 
 Questions. 
 172. What is the object of respiration ? 
 T73. Describe the arrangements in the lungs by which the air is 
 
 brought into close proximity to the blood. Describe a minute 
 
 lobule of the lung. 
 
 176. How much air passes in and out of the lungs of an adult man in 
 
 one hour? What change is effected in the air by respiration? 
 How is the capacity of the chest increased in inspiration ? 
 
 177. What are the different types of breathing ? 
 
 178. Give the number of respirations per minute at different ages. 
 
 179. How much air exists in the lungs of an adult man after the deepest 
 
 possible inspiration and after the deepest possible expiration ? , 
 
THE RESPIRATORY SYSTEM. 167 
 
 186. Abnormal Breathing. — There are three peculiar 
 forms of abnormal, that is to say, of unnatural breathing : (a) 
 apnma. When the blood contains an excess of oxygen, 
 respiratory movements either cease or become fewer in 
 number. If we take several deep breaths, as before 
 diving, we can 'hold the breath' for a longer time, {b) 
 dyspnoea, or difficulty in breathing. This may arise in a 
 variety of ways : (i) from puncture of the cavity of the 
 pleura, preventing expansion of the lungs ; (2) obstruction in 
 the air-passages, preventing the free passage of air to and 
 from the lungs, as in strangulation ; (3) profuse bleeding, 
 affecting the nervous mechanism of breathing ; (4) any- 
 thing that weakens the circulation ; {5) anything that 
 diminishes the extent of the respiratory surface, as in 
 many diseases of the lungs ; and (6) a deficient amount 
 of oxygen in the air. If the respiratory process is entirely 
 interrupted, as in choking, drowning, stoppage of the 
 movements of breathing by pressure on the chest, as when 
 one is wedged in a crowd, then we have {c) the state called 
 asphyxia, the symptoms of which are produced by accumula- 
 tion of carbonic acid in the blood. It is usually divided into 
 three stages, all of which can be traced in death by drown- 
 ing, (i) First, there is difficulty in breathing, or dyspncea. 
 The respiratory movements are hurried, irregular, and soon 
 'deeper and laboured ; the inspiratory and expiratory 
 muscles, more especially the former, contract powerfully, 
 ■and the muscles of the thoracic and abdominal regions 
 contract spasmodically. At the end of about one minute, 
 the spasmodic movements extend more or less to the 
 muscles of the extremities, chiefly affecting the flexors. 
 During this period the oxygen is being used up, the blood 
 is becoming more and more venous, and the respiratory 
 •centres in the medulla oblongata or bulb are excited by the 
 venous blood ; (2) Second stage. — The convulsions cease, 
 •and the movements of inspiration are scarcely perceptible, 
 
1 68 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 while those of expiration come powerfully into action. The 
 second stage also lasts about 07ie minute, and its pheno- 
 mena are due to the action of the highly venous blood on 
 the medulla oblongata and the spinal cord ; (3) Third stage. 
 — The pupils- are now dilated ; the eyelids do not shut on 
 touching the eyeball ; consciousness is abolished ; reflex 
 movements cease ; the muscles become loose or flaccid ; 
 and there is a state of calmness, which presents a striking 
 contrast to what was observed a minute before. The ordi- 
 nary inspiratory muscles act ,more feebly, and at longer 
 intervals of time, whilst the accessory inspiratory muscles 
 occasionally contract spasmodically, so as to produce a 
 series of convulsive gasps ; similar convulsive movements 
 now and then occur in the muscles of the extremities, 
 more especially in the extensors, the head is bent back- 
 wards, and the body may also be arched in the same 
 direction ; the nostrils are dilated ; the heart becomes 
 paralysed, its right cavities are very distended with venous 
 blood, which enfeebles the muscular tissue of the heart; 
 the pulse cannot be felt, and, after one or two con- 
 vulsive movements, death ensues. This period lasts from 
 two to three minutes, and the whole of the stages may be 
 completed in five or six minutes. The heart, however, 
 may beat for seven minutes. Recovery from asphyxia may 
 take place if artificial respiration is set up before the heart 
 ceases to beat. In cases of drowning, complete submersion 
 for three or four minutes is fatal. Newly-born animals 
 sustain immersion for a much longer time than adults. On 
 examining the body, the venous system generally, the right 
 cavities of the heart, and the capillaries of the lungs 
 are found to be full of dark venous blood, whilst the 
 arterial system is nearly empty, the elasticity of the great 
 vessels having driven the blood onwards. The blood 
 is very dark coloured, and its colouring matter is almost 
 entirely in the form of reduced haemoglobin — that is, 
 
THE RESPIRATORY SYSTEM. 1 69 
 
 hiemoglobin from which the respiratory oxygen has been 
 removed. 
 
 181. Ventilation.— A knowledge of the respiratory 
 process explains the benefit to be derived from ventilation. 
 Ten thousand parts of ordinary atmospheric air contain from 
 2 to 4 parts of carbonic acid gas. If this gas be present 
 to the extent of i^ to 3 parts in 1000, headache and 
 giddiness are felt-; and if it be increased to 20 parts in 
 1000, death will be the result. To secure a proper degree 
 of dilution of carbonic acid in a room, so as to render the air 
 fit for respiration, about 2000 cubic feet of fresh air should 
 be introduced every hour for each person living in the room. 
 
 182. Essential Nature of the Respiratory Process. 
 — Respiration may be divided into external and internal 
 breathing. By external breathing we mean the interchange 
 between the gases in the blood and the gases in the air 
 introduced into the lungs by the arrangements above 
 described. The venous blood comes to the lungs sur- 
 charged with carbonic acid gas, and containing too small 
 an amount of oxygen. In the air-cells, on the other hand, 
 we have a gas rich in oxygen, and containing relatively a 
 much smaller amount of carbonic acid gas than exists in 
 the blood. Carbonic acid gas thus escapes from the blood 
 into the air-cells, and oxygen is taken into the blood. The 
 oxygen taken Jn unites with the hcemoglobin in the red blood- 
 corpuscles, oxyhmmoglobin being formed. Thus the blood is 
 arterialised, having lost carbonic acid and having gained 
 oxygen. The arterial blood then passes to the tissues, and 
 here we come to the domain of internal breathing. All 
 living tissues breathe— that is -to say, they produce carbonic 
 acid and consume oxygen. They must get rid of the 
 excess of carbonic acid, otherwise it would act injuriously, 
 and they must receive new supplies of oxygen. This is 
 accomplished by the lymph and by the blood. The lymph, 
 as already seen (p. 148), comes from the blood, bathing 
 
1.7° ELEMENTARY HUMAN PHYSIOLOGY. 
 
 each element of tissue, and internal breathing is the inter- 
 change between the gases of the blood and lymph and the 
 gases of the tissues. The blood brings oxygen near to the 
 tissue by the oxyhsemoglobin, the oxygen-carrier; the 
 oxygen is given up to the lymph ; from the lymph the 
 tissue takes it up ; the tissue produces carbonic acid ; this 
 it gives up to the lymph ; and by the lymph it is passed 
 back to the blood. The blood having lost oxygen and 
 gained carbonic acid, is now venous, and it goes on to the 
 lungs to again get rid of its excess of carbonic acid gas 
 and receive a new supply of oxygen. Thus the pigment 
 of the blood is the oxygen-carrier, and research has shown 
 that the carbonates and phosphates of soda in the blood 
 are the carbonic acid carriers. 
 
 Questions. 
 i8o. What are the three forms of abnormal breathing? Mention the 
 various ways in which asphyxia may be brought about. De- 
 scribe the stages of death by drowning. 
 
 181. State your reasons for asserting that a plentiful supply of fresh 
 
 air is essential to life. 
 
 182. Distinguish external from internal breathing. What are the 
 
 arrangements for the respiratory process in an active tissue, as 
 in a muscle ? 
 
 CHAPTER VIII. 
 
 NUTRITION AND SECRETION. 
 
 183. Nutrition. — The tissues of the body, such as 
 muscle, bone, nerve, or brain, are nourished by the blood. 
 But as this fluid is almost thd same in chemical composi- 
 tion in different parts of the body, and as the tissues differ 
 much in this respect from each other, each tissue must have 
 a selective power, whereby it selects from the blood the mate- 
 rial it requires for its growth. To secure healthy nutrition, 
 we must have (i) an adequate supply of blood. If any part 
 
NUTRITION AND SECRETION. I? I 
 
 of the body be not supplied with abundance of blood, its 
 actions are enfeebled ; and if the supply be cut off alto- 
 gether, it soon weakens and dies. (2) The blood must also 
 be healthy in quality. If affected by disease of any organ, 
 so that certain injurious materials are not eliminated, the 
 general nutrition of the body speedily suffers. To secure 
 proper nutrition, a part must (3) be subject to the influence 
 of the nervous system. Disease of the spinal cord causes 
 paralysis of the lower limbs, and the muscles become soft, 
 flabby, and diminish in size. Section of a nerve supplying 
 a part is often followed by destruction of the part by 
 ulceration. Finally (4), the part itself must be in a healthy 
 condition to secure proper growth. Any tissue which has 
 acquired any peculiarity of structure by previous disease 
 retains this peculiarity for many years ; but in course of 
 time the tissue tends to revert to its original condition. 
 This explains such phenomena as the perpetuation of 
 cicatrices and the influence of the vaccine virus. In the 
 latter case, the virus stamps a peculiar quality on the 
 blood and tissues, which modifies any subsequent attack of 
 smallpox. Growth is dependent essentially on the supply 
 of material to the tissues by the blood, and on the amount 
 of waste of tissue. If the supply exceed the waste, as in 
 childhood, the body increases in weight and power ; if the 
 supply and waste are equal, the body may remain in a 
 stationary condition for many years, as in middle life ; and 
 if the supply be much less than the waste, the body loses 
 weight and strength, as in old age. 
 
 184. Secretion. — Secretion is that function by means 
 of which certain fluids are separated from the blood for 
 further service in the economy. Various of these secretions, 
 such as the saliva, gastric juice, pancreatic juice, &c., have 
 been already described, but here we may briefly refer to 
 the process of secretion generally. However complicated 
 the structure of the various secreting glands may be, it is 
 
172 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 found on minute examination to consist of a delicate 
 membrane, called a basement-membrane, having blood- 
 vessels richly distributed under its attached surface, and 
 actively growing cells on its free surface. By foldings and 
 reduplications of these elements of structure, all secreting 
 glands are formed (fig. 111). The cells, however, are the 
 active agents. They select from the blood the materials 
 necessary, and elaborate these to form the secretion. These 
 cells may be directly influenced by the nervous system. 
 The secretion is not directly formed from the living matter 
 
 Fig. 111. — Diagram showing various forms of Secreting Structures : 
 
 A, general plan of a secreting membrane ; b, basement-membrane with cells, a, 
 on one side, and blood-vessels, c, on the other ; B, simple tubular (gastric 
 glands), /oUiculay (tonsils), and elongated tubular or convoluted glands (sweat- 
 glands) : C, compound tubular, as in kidney ; D, compound racemose, as in 
 salivary gland, pancreas, &c. ; E, simple racemose, two forms, as sebaceous 
 glands, &c. 
 
 (protoplasm) of the secreting cell. Intermediate substances 
 are formed, and some of the materials of the secretion may 
 not be set free till the moment they leave the living cell. 
 Thus cells that secrete mucus do not form mucus, containing 
 mucin, at once ; there is an antecedent body, a mucin- 
 producer, or, as it is called, mucinogen. Many, but not all, 
 secreting cells are developed, grow, live a certain time, 
 drop off from the membrane, and becoming ruptured, the 
 secretion is set free. Thus secretion is not opposed to 
 growth, as at one time supposed : it is dependent on the 
 growth of certain cells (fig. 33). 
 
THE KIDNEYS. 
 
 173 
 
 Questions. 
 
 183. What do you understand by nutrition? "What are the conditions 
 
 of healthy nutrition ? 
 
 184. Describe the structure of a secreting membrane. Draw a diagram 
 
 showing the various types of glands. 
 
 CHAPTER IX. 
 
 THE KIDNEYS. 
 
 185. General Description. — The human kidneys are 
 situated in the loins, one on each side of the spine 
 (fig. 39). A well-developed healthy kidney weighs about 
 six ounces. When 
 cut open (see fig. /f**K 
 
 112), we find a 
 cavity communica- 
 ting with the ure- 
 ter, U, the excre- 
 tory duct of the 
 kidney, and we ob- 
 serve also that the 
 organ consists of 
 two regions, which 
 are named, from 
 their position, the 
 external or cortical, 
 and the internal 
 medullary or sub- 
 stance. The medullary part consists of straight tubules, 
 which divide in twos as they pass outwards to the cortical 
 part ; while in the latter the tubes are extremely convoluted 
 (fig. 1 14). The tubules are termed tubuli uriniferi. They 
 are lined by irregularly shaped cells somewhat like those 
 of columnar epithelium (fig. 113). In the cortical part of 
 
 Fig. 112. — Longitudinal 
 
 Section of Kidney : 
 
 C, cortical substance ; M, medul- 
 lary substance : P, pelvis ; U, 
 ureter ; RA, renal artery. 
 
 Fig. 113.— Sec- 
 tion of a Urin- 
 iferous Tubule : 
 
 u^ section of tube ; 
 b^ epithelial cells. 
 
174 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 an injected kidney there are numerous small round balls of 
 capillaries called Malpighian bodies, after the celebrated 
 anatomist who first observed them. In man they are 
 about the rJirth of an inch in diameter. They consist of 
 a mass of minute capillaries supplied with blood by an 
 afferent vessel, and having also an efferent vessel to carry 
 the blood away. Each of these little balls is embraced by 
 
 Fig. 114. — Diagrammatic View 
 of Tubules, A, and Blood- 
 vessels, B, of Kidney. 
 
 Fig. 115. — Arrangements con- 
 nected with ^ Malpighian 
 Body: 
 
 «*, terminal branch of the artery, giving 
 the terminal twig, a/, to the Mal- 
 pighian tuft, »;, from which emerges 
 the efferent vessel, ef. Other efferent 
 vessels, ^, tf, e, are seen proceeding 
 from other tufts, and entering the 
 capillaries surrounding the urinifel> 
 ous tube, t. From this plexus of 
 capillaries the emulgent vein, ev^ 
 springs. 
 
 an infolding of the dilated end of one of the uriniferous 
 tubes, forming the capsule of Bowman, as seen in fig. 115. 
 The watery part of the urine is here • separated from the 
 blood, while the solid matter is excreted by the action of 
 the cells lining the tubules. 
 
 i86. SpecialPoints inStructure. — These are well seen 
 in fig. 114. At B we may observe straight arterial vessels 
 
THE KIDNEYS. 1 75 
 
 springing from arched vessels just at the junction of the 
 cortical with the medullary portions. The straight vessels 
 run towards the surface of the kidney, and give off the 
 afferent twigs to the Malpighian bodies. The efferent vessels 
 are seen breaking up into a second set of fine capillaries 
 (fig. 115), from which the veins originate. Observe also 
 the capsule surrounding the end of the tubule, the con- 
 voluted part of the tube, then a long tube that runs down 
 into the medullary part, and then returns to the cor- 
 tical part, to end in the straight discharging tubes seen 
 very black at A. The loop is called the looped tube of 
 Henle. 
 
 187. Characters of the Urinary Secretion.— 
 Urine is a clear, amber-coloured, faintly acid fluid, with a 
 bitterish taste, and an aromatic odour. It has a specific gravity 
 of about 1020. It contains (i) water ; (2) a small amount of 
 mucus from passages ; (3) urea, from the oxidation of nitro- 
 genous matter ; (4) uric acid, in the form of urates of soda 
 and potash ; (5) a number of less oxidised bodies in small 
 quantities, such as allantoin, xanthin, kreatinin, &c. ; (6) 
 colouring matter ; (7) odoriferous matter ; (8) salts, chiefly 
 chlorides of sodium and potassium, sulphates of soda and 
 potash, phosphates of soda and potash, phosphate of lime, and 
 phosphate of magnesia ; (9) a trace of sugar ; and (10) small 
 quantities of the gases oxygen, carbonic acid, and nitrogen. 
 In flesh-eating animals, urea is present in large amount ; very 
 little uric acid being found ; but in. the urine of vegetable 
 feeders, little urea and no uric acid are present, while hippuric 
 acid exists in considerable amount. 
 
 188. Mode of Action of the Kidney. — The true 
 secreting part of the kidney is the epithelium lining the 
 convoluted tubules. The water and saline matters pass 
 through the thin walls of the vessels forming the glom- 
 erulus of Malpighi, and thus enter the convoluted tubes. 
 The process by which water and saline matters are separated 
 is scarcely a filtrative process, as the cells lining Bowman's 
 
176 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 capsule exert a selective action. The fluid thus formed 
 contains an excess of water, and part of this excess is 
 absorbed into lymphatics from the tube forming the loops 
 of Henle, and thus re-enters the blood. 
 
 1,89. Quantity of Urinary Constituents.— One hun- 
 dred parts of urine passed by a healthy person'contain of water 
 96, and of -solids 4 per cent. The solids are partly organic 
 and partly inorganic. Of the organic solids, the percentages 
 are urea 2'8, uric acid -05, and kreatinin •!. There are also 
 traces of xanthin, hypoxanthin, oxaluric a,cid, hippuric acid, 
 and oxalic acid. The pigment urobilin is present only in very 
 small amount, and sometimes there may be a trace of indican. 
 Of the inorganic substances, the chief is chloride of sodium, 
 about i-S per cent.; of phosphoric acid, about -16 per cent., 
 united partly to alkalies, chiefly sodium, and alkaline earths — 
 namely, magnesia and lime. There are also small quantities 
 of sulphates. In twenty-four hours we may have eliminated, in 
 grains, of urea 480, uric acid 7-5, of common salt 300, and 
 of phosphoric acid 30 to 40. 
 
 190. Conditions influencing the Amount of Urink 
 — The normal amount is from 50 to 60 ounces daily, containing 
 i^ ounce of solids. It is, less in summer than in winter. 
 The amount seems to depend (l) on the intensity of the pres- 
 sure of the blood within the Malpighian tufts ; (2) on the 
 activity of the secreting cells ; and (3) on the quantity of water 
 or other diffusible matter taken into the system. 
 
 191. Separation and Discharge of the Urine.— The 
 urine is constantly being secreted by the kidney. It is carried 
 away to the bladder by a tube called the ureter — the bladder 
 serving as a reservoir (fig. 39). It collects in the bladder 
 until that organ is completely filled, when it is voided by con- 
 traction of the walls of the bladder, aided by the abdominal 
 muscles. The evacuation is partly voluntary and partl)t 
 involuntary. 
 
 Questions. 
 
 185. Describe the naked eye appearances of a section of a kidney. 
 
 186. Describe the circulation in the kidney. 
 
THE SKIN. 
 
 177 
 
 187. Enumerate the chief constituents of the urine. 
 
 188. How do you think the urine is formed ? 
 
 189. How much of each of the chief constituents of the urine is ehm- 
 
 inated daily? 
 
 CHAPTER X. 
 
 THE SKIN. 
 
 192. General Description. — This organ, continuous 
 at various points with the internal mucous surfaces, covers 
 the whole body, and 
 consists of two layers : 
 first, a hard epithelium, 
 composed of cells 
 more or less flattened, 
 called the epidermis 
 (figs. 116, a, and 
 117, V) \ and second, 
 of the dermis, cutis 
 vera, or true skin, 
 c, which is formed 
 of connective and 
 elastic tissue. Under- 
 neath the true skin 
 we find a layer of fat, 
 g. The surface of the 
 true skin is raised into 
 a series of papillae, b, 
 connected with the 
 sense of touch. We 
 find in the skin two 
 kinds of glands. The 
 sudoriparous or sweat 
 glands consist of a tube, coiled into a ball at the deeper 
 
 Fig. 116.— Vertical Section of the Skin : 
 rt, epidermis : b, papills: : c, dermis, or true skin ; 
 d, sweat-pores ; e, hair; f, sebaceous glands ; g, 
 fat-cells ; h, sweat-glands. 
 
178 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 part, and communicating with the surface by a spiral 
 duct (fig. 116, K). The sebaceous glands are small race- 
 mose glands, which usually 
 a open into the hair-follicles 
 (fig. 116, /), and secrete 
 h an oily fluid for lubricating 
 ?_ the hairs and surface of the 
 skin. 
 ■ v '" 193. Secretion OF Sweat. 
 
 JiS^ , ^ » — The chief excretion of the 
 '^ ~* 4 ^Vviat' rf®''^" '^ sweat, an acid watery 
 
 ' *'..*'j^* J ' I'^'^iilJ''^-* ^^^^ (having a small amount 
 
 ' "T ^; ^'^^ 
 
 of salts, chiefly chloride of 
 
 sodium, and a trace of or- 
 
 « ganic matter, chiefly urea, in 
 
 _^ solution), which is usually 
 
 -' carried off from the surface 
 
 Fig. IIT.-Section of Epidermis jn the form of vapour. The 
 
 from the Human Hand, highly . . ii r 
 
 magnified: ^ ^ amount varies greatly : from 
 
 A, horny layer, consisting of a, super- ^^e pOUnds in the twenty- 
 
 ficial horny scales; *, swollen out four hoUrS, tO One pOUnd. 
 
 horny cells ; c, stratum lucidum : B, rr.i_ . . i_ . • r ^i • 
 
 reternucosum, consisting of rf, prickle That the Separation of thlS 
 
 cells ; e, elongated cells near corium ; exCrCtioH Is important, is 
 
 y, a nerve-fibre. p^.^^^^ ^^ ^^^ j.^^^^ ^^^^ jf 
 
 the skin be varnished overj so as to prevent exhalation, 
 death speedily ensues. All the various modifications of 
 epidermis, such as hair, horn, nail, hoof, feathers, &c., may 
 also be regarded in the light of excretions. 
 
 194. Functions of the Skin. — The skin is (i) a pro- 
 tective covering for the parts underneath ; (2) an organ of 
 excretion — -separating sweat and sebaceous matter ; (3) an 
 organ concerned in certain parts with the senses of touch 
 and temperature ; and (4) partially as an absorptive and 
 respiratory organ, absorbing small quantities of aqueous 
 vapour, and giving off carbonic acid. 
 
animal heat. 1 79 
 
 Questions. 
 
 192. Describe a vertical section of the skin. Describe the structure of 
 
 the epidermis (see fig. 117). 
 
 193. What is sweat ? 
 
 194. Enumerate the functions of the skin. 
 
 CHAPTER XI. 
 
 ANIMAL HEAT. 
 
 195. All the processes hitherto described, whether physi- 
 cal or chemical, contribute to produce heat. The great 
 source of heat in the body is the oxidation processes which 
 take place in almost every tissue and in every organ. The 
 circulating blood acts as a conductor or distributer of heat, 
 so that the uniform temperature, taken in a partially pro- 
 tected place like the armpit (axilla), is about 98-4° Fahr. 
 In the mouth and rectum the temperature may be about 
 one degree higher. These matters have already been dis- 
 cussed in treating of the body in action (see p. 65). 
 Animals, such as man, which maintain a constant tempera- 
 ture, are called warm-blooded, while those which have no 
 constant temperature, and have a temperature usually 
 only a few degrees above that of the medium in which 
 they live, are called cold-blooded. The body is always 
 losing heat by radiation and conduction. To maintain 
 the body at a uniform temperature, whatever that of the 
 outside medium may be, arrangements are made by 
 which the amount of heat eliminated and the amount of 
 heat produced are kept at a balance. So-called warm- 
 blooded creatures have arrangements for the regulation of 
 temperature by which an equilibrium is maintained between 
 the amount of heat lost by the body and the amount of heat 
 liberated in the body; while cold-blooded animals have no 
 such arrangements. Thus by the use of clothes, by the 
 
l8o ELEMENTARY HUMAN* PHYSIOLOGY. 
 
 activity of the skin, by the nature of the food, and by the 
 
 amount of muscular exertion, the heat is maintained and 
 
 regulated. 
 
 Questions. 
 
 195. What is the temperature of the body in the armpit? Suppose a 
 man were exposed naked on a cold day, would his temperature 
 fall quch, and if not, why not ? How would a frog's tempera- 
 ture vary suppose it were taken into a warm room ? 
 
 CHAPTER XII. 
 
 ANIMAL MECHANICS. 
 
 196. Having already described the bones, joints, and 
 muscles, we now proceed to discuss briefly the mechan- 
 ical arrangements met with in the body, or the physiology 
 of movement (see also p. 25, par. 11). 
 
 197. Mechanical Arrangements of Muscles. — The 
 great majority of the muscles of the body are attached to 
 levers formed by the bones. Here the movable bone re- 
 presents a lever of which the fulcrum is the articulation 
 with the fixed bone, the power is employed at the point of 
 insertion of the contracting muscle, and the resistance may 
 be of various kinds according to the obstacles which tend 
 to prevent displacement of the movable bone (fig. 25). In 
 the body we find examples of levers of the first, of the 
 second, and of the third order. 
 
 198. Levers of the First Order. — Here we find the 
 fulcrum between the power and the resistance. As an 
 example, take the balancing of the head on the vertebral 
 column (fig. 2) : the fulcrum is the articulation between the 
 occipital bone and the atlas ; the resistance is the weight of 
 that part of the head and face in front of the articulation ; 
 and the power is applied behind at the point of insertion of 
 the muscles of the neck. The construction of the vertebral 
 column, the balancing of the trunk on the pelvis, and of the 
 
ANIMAL MECHANICS. l8l 
 
 leg on the foot, represent levers of the same kind. Usually, 
 in man, this order of lever is for the purpose of stability, but 
 we find it also in certain movements. For example, in 
 extending the fore-arm upon the arm — the fulcrum is the 
 elbow-joint, the power applied behind the articulation is the 
 insertion of the triceps, and the resistance is the weight of 
 the fore-arm in front of the articulation (fig. 27, d). 
 
 199. Levers of the Second Order. — Here the resist- 
 ance is between the power and the fulcrum. In this lever 
 the power-arm * is always longer than the resistance-arm. 
 As the forces are inversely proportional to the length of the 
 arms of the lever, a comparatively weak force will overcome 
 considerable resistance, and consequently this lever is 
 advantageous as regards expenditure of force. But it is 
 disadvantageous as regards rapidity of movement, for the 
 displacements of the two points of application are pro- 
 portional to the lengths of the arms of the lever. For 
 example, if the length of the power-arm =10 feet, and that 
 of the resistance-arm = i foot, a force of one pound would 
 move a resistance of ten pounds, but the point of applica- 
 tion of the power would move through ten feet, while that 
 of the resistance would be displaced only one foot. This 
 lever may be termed the lever oi power. It is not common 
 in the body. As an example, take the action of standing 
 on tiptoe. Here the fulcrum is the contact of the toes 
 with the ground ; the power is at the insertion of the 
 tendo Achillis, the strong ligament fixed into the os calcis, 
 or heel-bone ; and the resistance is the weight of the body 
 transmitted to the articulation between the tibia and 
 astragalus (fig. 22). 
 
 200. Levers of the Third Order. — The power is 
 between the resistance and the fulcrum. In this lever the 
 
 * The term arms of the lever is the distance which separates the fulcrum from 
 the point of application of the power or of the resistance. The one may be called 
 ihs J>6wer-ann and the other the resistance-arm. 
 
1 82 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 resistance-arm is always longer than the power-arm, and 
 while it is advantageous as regards swiftness, it is dis- 
 advantageous as regards expenditure of force. It may be 
 termed the lever of rapidity. It is the one common in the 
 movements of man. For instance, in the flexion of the 
 fore-arm upon the arm, the fulcrum is the articulation at 
 the elbow; the power is at the insertion of the flexors 
 {brachialis anticus, and biceps), and the resistance is the 
 weight of the fore-arm. The power is usually applied 
 in the body near the fulcrum, and the power-arm is 
 thus much, shorter than the resistance-arm, and hence 
 only small weights can be moved, but with great speed. 
 Thus the various movements of the body are rapidly per- 
 formed, and the clumsy form of the limb which would have 
 resulted had the power been applied near the resistance . is 
 obviated (fig. 25). 
 
 Simple movements such as are above described rarely 
 take place. Usually the movements which one bone makes 
 on another are not effected by one muscle, but by several, 
 which may be regarded as associated together for that 
 movement. Thus, in moving the arm, say from pronation 
 to supination with a slight degree of flexion or extension,, 
 many muscles act (fig. 26). 
 
 20I. Conditions of Equilibrium in the ^ody.— Posture. 
 — In the natural erect posture, the human body becomes a 
 rigid pillar without almost any muscular effort — the conditions 
 being that the centre of gravity is supported within the base 
 or surface between the points of contact of the soles of the feet 
 with the floor. The centre of gravity of the head is in front 
 of its point of support on the atlas, but the arrangements are 
 such as to secure equilibrium chiefly by the action of the liga- 
 ments which bind the occipital bone to the atlas and axis. 
 When the slight muscular effort required is withdrawn, as 
 during sleep, the head droops forwards, and the chin rests on 
 the chest. According to Weber, the centre of gravity of the 
 trunk is situated in front of the tenth dorsal vertebra, and 
 
ANIMAL MECHANICS. 
 
 183 
 
 \\ 
 
 a plumb-line dropped from it passes behind a line connecting the 
 two hip-joints, so that the trunk would tend to fall backwards 
 were it not attached anteriorly by a firm ligament to the femur. 
 The centre of gravity of the whole body 
 lies immediately in front of the promin- 
 ence of the sacrum (figs. 1 and 2), and a 
 line suspended from it would pass a little 
 in front of a line connecting the axes of 
 both ankle-joints, so that the body has a 
 tendency to fall forwards. This is pre- 
 vented partly by the wedging of the 
 astragali into the fork-like cavities formed 
 by the lower ends of the tibia and fibula 
 (fig. 20), and partly by the action of the 
 muscles forming the calf of the leg. As 
 already pointed out (p. 25), the weight of 
 the body falls upon an arch formed by 
 the bones of the foot. When standing 
 in the rigidly erect position, like that of 
 a soldier at ' attention,' the muscles on 
 the anterior aspect of the body and limbs 
 act slightly, so as to prevent the body 
 from falling backwards, while those on 
 the posterior aspect prevent it from fall- 
 ing forwards (fig. 118). In sitting, the 
 trunk rests on the iuder ischii (see fig. 
 18, c), and tends to swing forwards and 
 backwards on these. Thus there is an 
 anterior and a posterior sitting posture. 
 
 202. Locomotion. — In walking, the 
 pelvis is alternately supported by one 
 of the legs. Starting, for example, with 
 the right leg, the body is inclined for- 
 wards, the right foot raised, the right 
 leg advanced, and the foot put on the ground. 
 
 Fig. 118. 
 
 Muscles which maintain 
 
 the erect posture. 
 
 Then the left 
 
 heel is raised, but the toes of the left foot have not quitted 
 the ground when the right foot has reached it, so that 
 both feet are never off the ground at the same moment. The 
 action of the muscles of the left leg moves the body forwards, 
 
184 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 upwards, and to the right side. When the left foot has left the 
 ground, the body is supported on the right leg, and the left leg 
 swings forward like a pendulum to a position in advance of 
 the right foot, constituting the second step. Rapidity of walk- 
 ing depends on the length of the step and the duration of the 
 step, or the pendulum-oscillation of the leg. The pendulum- 
 oscillation is the quicker the shorter the leg, hence the step of 
 short-legged persons is quicker than that of long-legged ones. 
 In running, the action is more like that of a series of jumps — 
 that is to say, there are intervals in the step during which both 
 feet are off the ground at once. At the commencement of the 
 step in running, the active leg is strongly flexed, and then it is 
 extended with a kind of sudden jerk. 
 
 Questions. 
 
 197. Describe a lever. 
 
 198. Give an example of a lever of the first order ; (199) of the second 
 
 order ; and (200) of the third order, stating the position of the 
 fulcrum in each case. 
 
 199. What advantage is gained by the insertion of the tendon of the 
 
 biceps near the elbow-joint ? 
 
 201. Describe the arrangements for the maintenance of the erect pos- 
 
 ture without fatigue. Why may we become fatigued if we are 
 kept at ' attention ' for a long time ? 
 
 202. Describe ordinary walking. 
 
 CHAPTER XIII. 
 
 THE SENSES. 
 
 203. Introduction. — The senses are called into play 
 when the condition of the body has been affected to a 
 certain degree by external or internal agencies. A flash of 
 light, a sound, a touch, may so act upon the body as to be 
 followed by a sensation or mental state. Sensitiveness is a 
 property of all animals, and possibly of not a few plants. 
 Some animals, indeed, are so low in the scale of organisation 
 as to have no special parts set aside for the reception of 
 
THE SENSES. 185 
 
 sensory impressions, but every part of their body seems 
 alike fitted to recognise changes in its surroundings. As 
 soon, however, as we pass to the higher grades of animal 
 life, as in man, we find certain parts or organs of sense 
 whose duty it is to keep th^ body in relation to its 
 surroundings, and also a nervous system which receives 
 impressions and ensures the co-operation of all the indi- 
 vidual elements of the body one with another. 
 
 In order that sensations may be felt, we have a central 
 nervous system, or sensorium, from which nerve-fibres pass 
 outwards to all parts of the body, and at the ends of 
 the nerve-fibres certain structures or terminal organs, 
 which are so formed as to be capable of responding to 
 some special variety of impression. Thus the terminal 
 organ of the nerve of vision is insensitive to the vibrations 
 which, by acting upon the ear, originate changes leading to 
 the sensation of sound. The sensorium does not act as a 
 whole, but is differentiated so that one part is devoted to 
 one sense, another to another ; and when the nerves which 
 lead to these nerve-centres have been stimulated, it matters 
 not what the nature of the stimulus to the nerve has been, 
 the sensation experienced is always for each centre of one 
 and the same kind. Thus the visual centre always gives 
 rise to the sensation of seeing something, the auditory 
 centre to that of hearing, the olfactory centre to sensations 
 of smell, the gustatory centre to those of taste, and the 
 tactile centre to touch. But, over and above these special 
 forms of sensation, there are many vague or general sensa- 
 tions, such as those of heat or cold, of pain or fatigue, of 
 pressure, resistance, and the like, which may seem to be 
 felt in almost every part of the body ; and although each 
 of these has in all probability its special nerve-centre, yet 
 no special terminal organ seems to be necessary. 
 
 Special terminal organs, then, are developed for the 
 senses of sight, hearing, smell, taste, and touch. 
 
i86 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 
 ^'f 
 
 J. t--^L'7l|| 
 
 
 <n\ 
 
 -' II 
 
 Touch. 
 
 204. General. — The sense of touch, including that of 
 
 different degrees of heat, is possessed by the skin, by the 
 
 walls of the mouth and nostrils, and by the tongue, but it 
 
 is most highly developed on the 
 
 tips of the fingers. The essential 
 
 organs of this sense are the true 
 
 skin, containing capillaries, and 
 
 the terminations of sensory nerves. 
 
 On examining the surface of the 
 
 true skin by a magnifying-glass, we 
 
 can see a regular arrangement of 
 
 papillae, or cone-like projections, 
 
 ibout xhs^ of an inch in length 
 
 (fig. 116). In many of these 
 
 papillae there are found small, 
 
 „.„„„, , round or oval bodies made of hard 
 
 Fig. 119. — Touch-corpuscle: ., . , . 
 
 7 . ... fibrous tissue, havme a nerve-fibre 
 
 u^ layers of connective tissue of , » o 
 
 the true skin ; b, body of cor- coiled round them, and sometimes 
 puscie;rf,ar,nerve-fibrestwisted penetrating into their interior. 
 
 spirally round the corpuscle : c, ^ ° 
 
 nerve-fibres at the lower end of TheSe are Called tOUch-bodieS (fig. 
 
 the corpuscle; J nerve-fibre JLjgx ^Jj ggj.yg ^^ resisting 
 
 ending in little thickenings near ' -^ , . *^ 
 
 the upper end of the corpuscle, structures agamst which the nerve 
 
 Magnified 250 diameters. ^^^ ^,g prCSScd, and thuS the SCHSe 
 
 of touch may be intensified. The touch-corpuscles are the 
 chief terminal structures connected with the sense, but 
 there are others. At the margins of the lips, and in other 
 localities where the sense is very delicate, we find small 
 bladder-like bodies, having nerve-fibres passing into their 
 interior. These have been called end-bulbs. Again, in the 
 tissue below the skin in the palm of the hand and fingers 
 and the soles of the feet there are other corpuscles, larger 
 than either the touch-corpuscles or the end-bulbs, each 
 consisting of a number of folds, like the coats of an onion, 
 surrounding a core into which a nerve-fibre passes. These 
 
THE SENSES. 187 
 
 are the Pacinian bodies. Hairs also may be regarded as 
 organs of touch, since nerves are connected with the roots 
 or the bulbs. When one of these nerves is pressed upon 
 by the contact of any foreign body, 
 an impulse is produced which travels 
 to the brain, whereby we become con- 
 scious of the impression. This con- 
 sciousness, however, we refer not to the 
 brain, but to the part affected ; a sub- 
 jective power, which is the result of 
 experience, inherited and acquired. 
 
 205. Nature of Touch. — A sen- 
 sation of touch is produced by gentle 
 pressure. The most delicate contact 
 causes pressure. It is a familiar obser- 
 vation that all parts of the skin are 
 not equally sensitive. The method of 
 determining the degree of sensitive- 
 ness, first employed by Weber, consists Co>npasses of Weber, 
 
 ' ,. , ,, ,. or sesthesiometer. 
 
 in finding the smallest distance at 
 
 which the two points of a pair of compasses can be felt. 
 
 The results in millimetres* are given in the following table : 
 
 Fig. 120. 
 
 Tip of tongue i -i 
 
 Under surface of third 
 
 phalanx of finger 2-2-3 
 
 Red part of the lip 4-5 
 
 Under surface of second 
 
 phalanx of finger .4-4- 5 
 
 Upper surface of third pha- 
 lanx of finger, tip of nose.. 6-8 
 
 Ball of thumb 6-5-7 
 
 Centre of palm 8-9 
 
 Under surface of third 
 
 phalanx of great toe 11-3 
 
 Upper surface of second 
 
 phalanx of finger 11-3 
 
 * I millimetre 
 
 B ack, eyelid 11-3 
 
 Under surface of lower third 
 
 of fore-arm 15-0 
 
 Cheek 15-8 
 
 Temples and Forehead 22-6 
 
 Back of head 27-1 
 
 Back of hand 31.6 
 
 Knee 36-1 
 
 Fore-arm and leg 45-1 
 
 Back, opposite fifth dorsal 
 
 vertebra 51.1 
 
 Neck -••54-1 
 
 Upper-arm, thigh, centre of 
 
 back 67-1 
 
 : ^ of an inch.. 
 
1 88 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 206. Sensations of Temperature. — The skin is the 
 chief organ by which we appreciate temperature. Sensations 
 of heat and cold can also be excited in mucous surfaces. 
 Direct irritation of a nerve does not give rise to these sensa- 
 tions. Thus if we plunge the elbow into very hot water, 
 or into ice-cold water, we do not experience heat or cold 
 by thus irritating the ulnar nerve, which lies here just below 
 the skin, but there is a painful sensation referred to the 
 extremities of the nerve. Recent observations show that 
 
 , there are minute areas 
 
 •* •> *• * 
 •■;;'•. "."K. •' ..•. . • : ••• •••.••. of skin in which sensa- 
 
 -•- -• • tf%*« - «••••• ■• »• 
 
 "" • -■ -- tions of heat and cold 
 
 .'•>,•..;»• ...V. ;>«'-N.jj:;'* ': 
 
 may be more acutely 
 .-. .. .y, » felt than in adjoin- 
 :•.•.'• '; •••/:: ing areas. Some of 
 * ' these areas are more 
 Fig. 121. sensitive to cold, and 
 
 C, cold spots ;H, hot spots. ^^^^^ ^^^ ^^jj^^ ^^^^ 
 
 spots ; while others, more sensitive to heat, have received 
 the name of hot spots ; and they appear to be, or to con- 
 tain, end-organs, arranged in points, subservient to a tem- 
 perature-sense. A topographical view of such spots on 
 the radial half of the dorsal surface of the wrist is 
 shown in fig. 121. A simple method of demonstrating 
 this curious phenomenon is to use a solid cylinder of 
 copper, say eight inches in length by \ inch in thickness, 
 and sharpened at one end to a fine pencil-like point 
 Dip the pointed end into hot water, close the eyes and 
 touch parts of the skin. When a hot spot is touched, 
 there is an acute sensation of burning. Such a spot is 
 often near a hair. Again, in another set of experiments, 
 dip the copper pencil into ice-cold water and search for the 
 cold spots. When one of these is touched, a curious 
 sensation of cold, as if gathered to a point, is experienced. 
 It will be found, in this way, that in a given area of skin 
 
THE SENSES. 1 89 
 
 there may be hot spots, cold spots, and tactile spots. Cold 
 spots are more abundant than hot spots. The spots are 
 arranged in curved lines, but the curve uniting a number 
 of cold spots does not coincide with the curve forming a 
 chain of hot spots. 
 
 Questions. 
 
 203. What do you mean by sensitiveness and sensation ? What are 
 
 the parts necessary for a serisation ? 
 
 204. Describe the various kinds of tactile bodies. 
 
 205. How may tactile sensibility be measured ? Where are the most 
 
 sensitive portions of the skin ? 
 
 206. What evidence is there that we can appreciate heat and cold by 
 
 the skin, say of the forefinger ? 
 
 Taste. 
 
 207. General. — The organs of taste are in the mucous 
 membrane of the tongue, especially at its back part. The 
 nerves of taste are the lingual branch of the fifth cranial 
 nerve and the glosso-pharyngeal, the former supplying the 
 
 Fig. 122. — Organ of Taste from Tongue of Rabbit : 
 a, section through taste-organ^ showing flask-shaped bodies in the depressions ; 
 ^, flask body isolated, showing that it is made of spindle-shaped cells ; c, small 
 cells found in flask, having pointed lower ends which are continuous with nerve- 
 fibres ; d, fusiform cells which form wall of flask-shaped body. 
 
 anterior two-thirds, and the latter the posterior one-third 
 of the tongue. The chorda tympani, a branch of the 
 facial, is also a nerve of taste for the tip of the tongue. 
 The mucous membrane of the tongue presents papillae of 
 various forms, known asjiliform, or thread-like ; fungiform, 
 
19° ELEMENTARY HUMAN PHYSIOLOGY. 
 
 or mushroom-like; and circumvallate. The circumvallate 
 papillae are from thirteen to fifteen in number, and are 
 set in the form of a V with its point backwards. Each 
 resembles a broad fungiform papilla surrounded by a trench. 
 The terminal organs of taste are flask-shaped bodies, well 
 seen in the tongue of the rabbit (fig. 122), and abounding 
 in the circumvallate papillae. They derive their nerves 
 chiefly from the glosso-pharyngeal nerve. The contact of 
 a sapid body with the surface of the tongue is not sufficient 
 to evoke the sense of taste. The substance must be 
 dissolved, and to effect its solution a special fluid is 
 provided — the saliva. In febrile diseases, in which the 
 tongue is dry and coated, the sense of taste is either 
 dormant or perverted. Taste is more acute in some per- 
 sons than in others. 
 
 208. Physiological Conditions of Taste. — The 
 tongue is the seat of sensations that are quite unlike each 
 other. Thiis, there are tactile sensations, as when we 
 touch the organ with a pin, sensations of pressure, sensa- 
 tions of heat and of cold, burning or acrid sensations, 
 peculiar sensations excited by the application to the tongue 
 of an interrupted electrical current, and, lastly, sensations 
 of true tastes. We must also distinguish from these 
 sensations that are called flavours, experienced when we 
 bring the tongue into contact with an onion or a savoury 
 bit of cooked meat or fish. These are in reality sensations 
 compounded of smells and tastes, and the sensation of 
 tasting an onion is thus quite changed when we hold the 
 nose and avoid breathing. True tastes may be classified 
 as sweet, bitter, salt, sour, alkaline, and, perhaps, metallic. 
 All of these are specifically distinct sensations, and they are 
 no doubt due to some kind of action, probably chemical, 
 which the substance excites in the taste-cells. If we assume 
 that the taste-cells are connected with the ends of the 
 nerves, then we can imagine that the chemical changes 
 
THE SENSES. 
 
 191 
 
 excited in the taste -cells set up nerve impulses which, 
 propagated to the centre of taste in the brain, give rise 
 there to molecular changes that in turn are related to 
 consciousness. 
 
 Questions. 
 
 207. What are the nerves of Ihe tongue ? Describe the papillae on the 
 
 surface of the tongue. 
 
 208. What sensations may be referred to the tongue ? 
 
 209. 
 
 Smell. 
 I. General. — The organ of the sense of smell is the 
 
 .1 
 
 Fig. 123. — Transverse vertical section across the 
 nasal cavities, opposite to the middle of the hard 
 palate ; the anterior part of the section seen from 
 behind : 
 
 I, part of inner surface of cranium ; 2, projection between the 
 two cribriform plates of the ethmoid bone ; 3. median septum 
 or partition in the ethmoid bone ; 4, 4, cells in the lateral 
 masses of the ethmoid bone ; 5, 5, the middle turbinated 
 portion of the ethmoid bone ; 6, 6, the two turbinated bones ; 
 
 7, the vomer, or bony septum or partition, of the nose ; 
 
 8, section of the malar or cheek bone ; 9, a large sinus or 
 space in the superior maxillary bone — sometimes called the 
 maxillary sinus, or antrum of Highmore ; it communicates 
 with the nasal cavity, at 10, and there is a corresponding 
 space on the other side. 
 
 mucous membrane lining a part of the nasal cavities 
 
 Fig. 124. 
 
 ' Cells from the 
 olfactory or- 
 gan, of two 
 kinds : 
 
 Uy with broad 
 ends like 
 knife - handles ; 
 c", with deli- 
 cate pointed 
 ends, and con- 
 tinuous with 
 nerve - fibre at 
 d. 
 
192 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 supplied with nerves from the olfactory bulbs or first pair 
 of cranial nerves. Attached to the side walls of each nasal 
 cavity are two, delicate scroll-like bones, called turbinated 
 bones (see fig. 123), which to a great extent divide each 
 cavity into three spaces, lying one above the other (fig. 
 123). The upper two of these constitute the true olfac- 
 tory chambers, while the lowest passage is merely used 
 for respiratory 2:)urposes. The whole of this bony frame- 
 work is covered by moist mucous membrane, covered by 
 elongated cells attached to the ramifications of the olfactory 
 nerves (fig. 124). By the contact of certain substances 
 with these, a sensation of smell is produced. All odorous 
 substances are in general such as can be readily acted on 
 by oxygen. Animal effluvia exist near the soil, hence the 
 bloodhound runs with his nose to the ground. The sense 
 of smell is extremely delicate in most individuals. It is 
 soon blunted, and consequently many who live among 
 disagreeable odours do not perceive them. A distinction 
 must be drawn between a smell proper, like that of a violet, 
 and the irritation produced by the fumes of ammonia. 
 The close stuffy sensation experienced on entering an ill- 
 ventilated crowded apartment, is due partly to interference 
 with the free play of respiration, and partly to the odour 
 of certain organic matters given off by the breath. 
 
 210. Physical Causes of Smell. — Substances that 
 excite the sense of smell must exist in the atmosphere in 
 a state of fine subdivision, and even vapours and gases may 
 be supposed to consist of minute molecules of matter. If 
 air conveying an odour be passed through a long glass 
 tube packed firmly with cotton-wool, it will still be odorous, 
 although this proceeding will remove all particles larger 
 than the one-hundred-thousandth of an inch. Again, a 
 grain of musk will for years communicate its odour to the 
 air of a room, and at the end of the time it will not have 
 appreciably diminished in weight. Odoriferous particles 
 
THE SENSES. 193 
 
 will mix with the air either in accordance with the laws of 
 diffusion of gases or by virtue of their volatility, that is, 
 the rapidity with which they evaporate. In the case of 
 odorous gases, no doubt mixture takes place by diffusion, 
 but an odorous essential oil will give off particles by a 
 kind of evaporation. 
 
 211. Physiological Conditions of Smell. — The air 
 containing the odour must be driven against the mem- 
 brane. The nostrils may be filled with an odoriferous 
 substance like eau-de-cologne, or air impregnated with 
 sulphuretted hydrogen, and no smell will be experienced 
 if no inspiration is made. When we make a sniff, the air 
 in the nasal passages is rarefied, and as the odour-bearing 
 air rushes in to equilibrate the pressure, it is forcibly 
 driven against the olfactory surface. Odorous air passing 
 from the posterior nares also gives rise to sensation of 
 smell, although not so intense as when it passes in the 
 normal direction. An odour may be perceived even 
 although the nostrils are full of fluid. 
 
 Questions. 
 
 209. Describe a vertical section through the middle of the nose, and 
 
 indicate where the sense of smell is located. Describe the 
 terminal organ of smell. 
 
 210. What are the physical causes of odours? 
 
 211. Given an odoriferous substance, what is necessary to excite 
 
 smell ? 
 
 Sight or Vision. 
 
 212. General. — The sensation of light results from the 
 influence produced indirectly on the expansion of the 
 filaments of the optic nerve by vibrations of a delicate 
 and subtle substance known as the 'ether.' But the falling 
 of light upon the optic nerve itself will produce no sensa- 
 tion. An intermediary apparatus is necessary — the retina, 
 which is an expansion of nervous matter intimately con- 
 
 M 
 
194 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 nected with or related to the terminal filaments of the 
 optic nerve. The action of light on the retina is analogous 
 to that produced on a photographic surface, and it is 
 associated with a change in the electrical condition of the 
 retina. 
 
 213. General Description of Eye. — The. globe of the 
 eye is placed in the anterior part of the orbit, in which it 
 is held in position by its connection with the optic nerve 
 
 Fig. 125. 
 
 View of lower half of right Human Eye, divided horizontally : 
 
 a, cornea ; ^, sclerotic ; r, sheath of optic nerve passing into sclerotic ; d^ choroid ; 
 e, ciliary muscle ; /, ciliary process : g, iris ; h, optic nerve with artery in 
 centre ; z, passage of nerve into retina, called optic disc or papilla ; k, fovea 
 centralis in centre of yellow spot ; /, retina ; m, anterior chamber of aqueous 
 humour ; «, posterior chamber of aqueous humour ; 0, crystalline lens ; /, 
 zonule of Zinn ; q, suspensory ligament of lens; r, vitreous humour. 
 
 posteriorly, and with the muscles which surround it, and 
 by the eyelids in front. It is further supported behind and 
 on the sides by a quantity of fat. The eyeball is composed 
 
THE SENSES. 1 95 
 
 of several investing membranes, and of certain transparent 
 structures, which are enclosed within them. These trans- 
 parent structures act as refractive media of different 
 densities, so that rays of light entering the eye are so bent 
 as to come to a focus on the retina. As rays of light may 
 be supposed to emanate from the surface of any external 
 object, a distinct image is formed. These refractive 
 structures are, from before ' backwards — ist, the cornea, a 
 transparent epidermic structure (fig. 125, a) ; zd, the 
 aqueous humour in the anterior chamber, m ; 3d, the lens, 
 composed of numerous laminae, like the folds of an 
 onion, ; and lastly, the vitreous humour, a jelly-like 
 structure, r. 
 
 214. The outermost coat of the eye is the sclerotic, b. It 
 is a strong, dense, white, fibrous structure. Posteriorly, it 
 is perforated by the optic nerve. This coat, by its great 
 strength and comparatively unyielding structure, maintains 
 the inclosed parts in their proper form, and serves to 
 protect them from external injuries. 
 
 215. The choroid coat, d, is a dark-coloured vascular 
 membrane, containing pigment cells (see fig. 50). In 
 front, it ends in the ciliary processes, f, which consist of 
 about sixty or seventy radiating folds. These fit into 
 depressions in the suspensory ligament of the lens, q, and 
 assist in keeping it in its proper position. 
 
 216. The iris, g, may be regarded as a process of the 
 choroid, with which it is continuous. It is a thin, flat curtain, 
 hanging vertically in the aqueous humour in front of the 
 lens, and perforated by the pupil for the transmission of 
 light. It is composed of unstriped muscular fibres, one 
 set of which being arranged circularly round the pupil, 
 when necessary, effect its contraction ; while another set 
 lie in a radiating direction from within outwards, and 
 by their action dilate the pupil. Thus more or less 
 light may be admitted into the eye, and the function of 
 
196 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 the iris is like that of the diaphragm in many optical 
 
 instruments. 
 
 217. The varieties of colour in the eyes of different 
 
 individuals and of different kinds of animals mainly depend 
 upon the amount of the pigment 
 which is deposited in the cells in 
 the substance of the iris, and upon 
 the thickness and degree of trans- 
 lucency of the iris. 
 
 218. Within the choroid is the 
 retina (fig. 125, /). With the naked 
 eye it is seen to be a delicate 
 semi-transparent sheet/of nervous 
 matter, lying immediately behind 
 the vitreous humour, and extend- 
 ing from the entrance of the optic 
 nerve nearly as far as the lens. 
 On examining the retina at the 
 back of the eye by an instrument 
 called an ophthalmoscope, we ob- 
 serve, directly in a line with the 
 axis of the globe, a circular yellow 
 spot called, after its discoverer, 
 the yellow spot of Sommering, k. 
 ■ ,„„ ^. The only mammals in which it 
 
 Fi& 126. — Diagrammatic . •' , , , 
 
 Section of Human Retina: exists are man and the monkey. 
 
 „, layer of hexagonal pigmented It IS the pomt of dlStinCt VlSlOn. 
 
 cells ; b, layer of rods and When We read & book, wc ruu the 
 
 cones (Jacob's membrane); c, , .it . i ■ 
 
 external granules layer, with eye aloHg the lines SO as to bnng 
 
 oval granules ; d, external reti- portions of the lineS SUCCeSsively 
 cular layer of fine fibrils : f, in- ... .. . Tr j.u 
 
 ternal granular layer ;/, inter- On the ycUow SpOt. If, On the 
 
 nal reticular layer; g, nerve- Other hand, WC carcfully fix OUr 
 
 cells , h, fibres of optic nerve. ^^^^^^^^^ ^n a word in the middle 
 of the line, we see that word distinctly, because its image is 
 on the yellow spot ; while the images of the words towards 
 
THE SENSES. 197 
 
 each end of the line are less distinct, being on other and 
 less sensitive portions of the retina. 
 
 219. The structure of the retina, as revealed by the 
 microscope, is seen in fig. 126. It is now well known that 
 the part affected by light is the layer of rods and cones 
 next the choroid, so that a ray of light passes through all 
 the other layers ere it reaches this sensitive layer. Each 
 rod or cone is probably in direct communication with a 
 filament of the optic nerve, so that, when excited by light, 
 an impulse is transmitted along this filament to the brain, 
 and the consequence is a luminous impression. 
 
 220. The TRANSPARENT MEDIA through which rays of 
 light must pass before they form on the retina the images 
 of external objects are : 
 
 (i) Immediately behind the transparent cornea is the 
 aqueous humour, which fills up the chamber between the 
 cornea and the lens (fig. 125, tn). It is nearly pure water, 
 with a trace of chloride of sodium. 
 
 (2) The crystalline lens lies opposite to and behind the 
 pupil, close to the iris, and its posterior surface is received 
 into a depression on the fore-part of the vitreous humour 
 (fig. 125, 6). In form it is a double convex lens, with sur- 
 faces of unequal curvature, the posterior being the more 
 convex, and the curvature is also less at the centre than 
 towards the margin. 
 
 (3) The vitreous humour lies in the concavity of the 
 retina, and occupies four-fifths of the eye posteriorly (fig. 
 125, r). 
 
 221. The APPENDAGES of the eye are : 
 
 (i) The muscles by which the eye is moved are four 
 straight (or recti) muscles, and two oblique (the superior 
 and inferior). By the duly associated action of these 
 muscles, the eye is enabled to move through a consider- 
 able range without the head being moved. 
 
 (2) The eyelids are two thin movable folds placed in front 
 
igS ELEMENTARY HUMAN PHYSIOLOGY. 
 
 of the eye, to shield it from too strong light, and to protect 
 its anterior surface. The eyelashes intercept the entrance 
 of foreign particles directed against the eye, and assist in 
 shading that organ from an excess of light. 
 
 (3) The lachrymal apparatus consists of the lachrymal 
 gland, by which the tears are secreted ; two canals, into 
 which the tears are received near the inner ang^le of the 
 eye ; the sac, into which these canals open ; and the duct, 
 through which the tears pass from the sac into the nose. 
 The constant movements of the upper eyelid induce a con- 
 tinuous gentle current of tears over the surface, and these 
 carry away any foreign particle that may have been 
 deposited on the globe of the eye. 
 
 222. Mechanism of Vision. — ^The uses of the different 
 structures of the eye are readily understood. Assuming a 
 general knowledge of the ordinary laws of geometrical 
 optics, let us trace the course of the rays of light pro- 
 ceeding from any luminous body through the different 
 media on which they impinge. If a luminous object, as, 
 for example, a lighted candle, be placed at the ordinary 
 distance of distinct vision (about ten inches) from the 
 front of the eye, ■ some rays fall on the sclerotic, and being 
 reflected, take no part in vision ; the more central ones 
 fall upon the cornea, and of these some also are reflected, 
 giving to the surface of the eye its beautiful gUstening 
 appearance, while others pass through it, are strongly 
 converged by it, and, entering the aqueous humour, are 
 proisably also slightly converged there. Those which fall 
 on and pass through the outer or circumferential part of 
 the cornea are stopped by the iris, and are either reflected 
 or absorbed by it ; while those which fall upon its more 
 central part pass through the pupil. The rays now 
 impinge upon -the lens, which, by the convexity of its 
 surface, and by its greater density towards the centre, 
 increases the convergence of the rays passing through it. 
 
THE SENSES. 199 
 
 They then traverse the vitreous humour, the principal use 
 of which appears to be to afford support to the expanded 
 retina, and are brought to a focus upon that tunic, forming 
 there an exact, but inverted image of the object (fig. 130). 
 
 nent. For example, if we look through 
 
 223. Accommodation of the Eye for Distance.— It 
 will be found that we cannot distinctly see a distant and a near 
 object at the same moment. For example, if we look through 
 a railing at a distant 
 church spire, and fix 
 our attention on the 
 spire, we do not dis- 
 tinctly see the railing ; 
 and vice versa. This 
 was early observed ; 
 but, until recently, the ^ ^ 
 
 mechanism by which Fig- 127.— ReHected images in the eye : A, 
 the eye accommodates ^°^ distance ; B, for near vision, 
 
 or focuses itself for different distances was unknown. Cramer 
 was the first to point out that if we bring a candle-flame near 
 the eye in a dark room, we may see three images — ist, an erect 
 image reflect- j^ 
 
 ed from the 
 cornea; 2d, an 
 erect image 
 on the anterior 
 surface of the 
 lens ; and 3d, 
 an inverted 
 and very faint 
 image on the 
 posterior sur- 
 face of the 
 lens. He also 
 showed that 
 when the eye 
 looks quickly 
 
 at a near object, after having been for some time directed to 
 a distant one, the middle image moves forwards nearer to the 
 
 liary Muscles and Iris in 
 
 accommodation ; 
 
 A, (right or left) half; eye at rest, or focused for a distant 
 object. B, (left or right) half; eye focused for a near object. 
 
 a, cornea ; ^, sclerotic : c, anterior part of choroid : d^ ciliary 
 muscle ; e, suspensory ligament of lens ; f, anterior capsule 
 of lens ; ^, iris. 
 
200 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 first, and also becomes smaller, showing that for near vision 
 the anterior surface of the lens becomes more convex (see 
 fig. 127). Thus he showed conclusively that the accommoda- 
 tion of the eye for different distances is effected by changes 
 in the curvature of the anterior surface of the lens. The 
 physiological explanation is as follows : 
 
 The lens, which is elastic, is kept habitually in a state of 
 tension by the pressure of the suspensory ligament (fig. 125, q), 
 and consequently has a flatter form than it would take if left 
 to itself. The ciliary muscle (fig. 125, e) contracts when 
 we look at a near object. When contracting, by pulling on 
 the ciliary processes (fig. 125,/), it relaxes the ligament, and 
 thereby diminishes its elastic tension upon the lens. The 
 anterior surface of the lens consequently becomes more con- 
 vex, and thus the divergent rays from a near object are brought 
 to a focus on the retina. The lens returns to its former shape 
 when the ciliary muscle ceases to contract (see also fig. 128 
 and description). The power of thus accommodating the eye 
 begins when we look at objects about 70 yards, and ends at a 
 distance of about 10 inches from the eye. 
 
 Questions. 
 
 213 and 220. What are the refractive media through which light 
 
 must pass before it reaches the retina ? 
 
 214 to 2i8. Suppose you cut from the outside of the sclerotic to the 
 
 centre of the eye, through what layers would the incision be 
 
 made ? 
 216. Describe the structure of the iris. 
 218, 219. Describe the layers of the retina. 
 
 220. Draw the form of the lens. 
 
 221. Describe the lachrymal apparatus. 
 
 222. Show how an image, say of an arrow, is formed on the retina. 
 
 223. Prove that the eye must be focused for objects at different dis- 
 
 tances. What is the mechanism of accommodation ? 
 
 224. The Blind Spot.— Near the area of greatest sensi- 
 bility to light we have a spot in the retina which is devoid of 
 rods and cones, and hence is unaffected by images formed upon 
 it. This is the optic papilla (fig. 125, i), or place of entrance 
 of the optic nerve, and as its diameter is nearly rifth of an 
 inch, it subtends a visual angle of about 6 degrees. Lines 
 
THE SENSES. 20I 
 
 drawn from the border of the optic pore to the nodal point 
 (the point where central rays cross in the lens), and pro- 
 duced outwards, will enclose a flattened cone whose base is 
 contained within the visual field, and within which all objects 
 will be invisible to the unmoving eye. This area is called 
 the blind spot. Suppose, for example, the left eye being shut, 
 the right eye be fixed upon the cross. When the book is held 
 
 at arm's length, both cross and round spot will be visible ; but 
 if the book be approximated to about 8 inches from the eye, 
 the gaze being kept steadily upon the cross, the round spot will 
 at first disappear, but as the book is brought still nearer both 
 cross and spot will again be seen. It may also be noted in 
 this experiment, that there is no consciousness of a break 
 of continuity in the visual field, no sensation, as we might 
 imagine there would be, of darkness ; to put it shortly, there 
 being no stimulation, there is not consciousness of a lack, but 
 a lack of consciousness. 
 
 225. Defects of Vision.— It has been shown that the 
 human eye is not a perfect optical instrument in the sense 
 of being accurately corrected for spherical and chromatic 
 aberration, but it is so nearly perfect in this respect that the 
 defects escape our notice unless looked for with special appli- 
 ances, and consequently we suffer no practical inconvenience. 
 In some people there is a defect called astigmatism, in which 
 the individual cannot see at the same distance, and in the 
 same plane, a horizontal and vertical line with equal dis- 
 tinctness. It is usually due to differences in the curvatures 
 of the vertical and horizontal meridians of the cornea. There 
 are two common forms of defective vision, however, which re- 
 quire notice — namely, short-sightedness or myopia, and long- 
 sightedness or hypermetropia. They are due to an abnor- 
 mality either in the curvatures or in the density of the refract- 
 ing media, or in the length of the horizontal axis of the eyeball. 
 In short-sightedness, from too great a refractive power from 
 either cause, the rays from objects at the ordinary range of 
 distinct vision are brought too soon to a. focus, so as to cross 
 one another, and to diverge before they fall on the retina ; the 
 
202 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 eye, in this case, being able to bring to the proper focus on the 
 retina only those rays which were previously diverging at a 
 large angle from a very near object (fig. 129, C). The correc- 
 tion for this deficiency is accomplished by interposing between 
 the eye and indistinctly seen objects a concave lens, with a 
 curvature sufficient to throw the 
 images of external objects at the 
 ordinary distance of distinct vision 
 backwards upon the retina. In 
 long-sightedness, on the other 
 hand, there is an abnormal dimi- 
 nution of the refractive power, or 
 the eyeball is too short from before 
 backwards (fig. 129, B), so that 
 the focus is behind the retina. 
 This defect is corrected by a 
 convex lens, which increases the 
 convergence of the rays of light. 
 The normal eye is seen in fig. 
 129, A : by it parallel rays, such 
 as come from objects at a great 
 distance, are focused on the 
 retina. 
 226. Subjective Phenomena 
 -When small particles 
 of matter occur in the aqueous 
 or in the vitreous humour, they 
 cast shadows on the retina which 
 
 Fig. 129. 
 
 A, normal eye : parallel rays 
 brought to a focus at retina. B, 
 hypermetropic eye : globe short- 
 ened ; parallel rays not yet brought 
 to a focus when they reach retina. 
 C, myopic eye : globe lengthened ; OF VISION.- 
 parallel rays brought to a focus in 
 front of retina. In astigmatism the 
 vertical meridian of the cornea is 
 usually the more convex. 
 
 appear to float in the air before the eye, often like small 
 black dots, but sometimes assuming grotesque forms. These 
 are called muscce volitantes. They are often seen during ill 
 health, more especially if associated with bilious disorder. 
 Another series of phenomena are produced by pressure on the 
 eyeljall, either continuous, or sudden as by a blow. Then a 
 number of rings of various colours, or a flash of light, may be 
 observed. These are termed phosgenes, and are due to 
 mechanical irritation of the retina. Finally, if we fix the 
 attention for a minute or two on a coloured surface, say a red 
 wafer, brilliantly illuminated on a white ground, and then 
 
THE SENSES. 203 
 
 transfer the gaze to another part of the room, or shut the 
 eyes, in a second or two a huge wafer, of a colour com- 
 plementary to the one at first looked on— that is, green— makes 
 its appearance, and floats before us. Such phenomena are 
 termed after-images, and are accounted for by supposing that 
 the light from an illuminated surface fatigues a limited area 
 of the retina, and that the after-image is due to the changes 
 in the retina which attend its recovery from this fatigue. The 
 three classes of phenomena just described are all examples of 
 optical illusions, and must be distinguished from the delusions 
 of the insane, which have their origin not in the sense organ, 
 the eye, but in the brain. 
 
 227. Position of Objects on the Retina. — In con- 
 sequence of the bending of rays of light by the refractive 
 media, the image of an external object is inverted on the 
 retina, and yet we see objects erect. The probable explan- 
 ation is, that the mind may perceive as correctly from 
 an inverted as 
 from an erect 
 image. When 
 we glance at ' 
 a column from 
 top to base, 
 
 we move the Fig. 130.— Diagram showing the visual angle, and 
 eyeball down- also the path of rays through the eye. 
 
 wards so as The image of the point, A, is formed on the retina at a; of B 
 
 , , • ^ at ^ / and of C at c. AOC is the visual angle. On the 
 
 10 Drmg sue- retina there is an inverted image, cia, of the object, ABC, 
 
 Cessive parts *"^ '^^ size of this image depends on the size of the 
 
 on the yellow ^"^° 
 
 spot, and it is the feeling of movement which informs us 
 which is top and which is base, not the inverted position 
 on the retina, of which we are unconscious. 
 
 228. Sizes of Objects. — The apparent size of any 
 object depends on the size of the image formed on the 
 retina, and this again on the size of the visual angle — that 
 is, the angle formed in the lens by the pencils of rays 
 
204 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 passing from the extreme limits of the object looked at (see 
 fig. 130 and description). 
 
 229. Single Vision with Two Eyes. — This pheno- 
 menon is explained by the fact that there are corresponding 
 points on the retina, so that when, by an adaptive action 
 of the muscles of the eyeball, an image is formed on a cor- 
 responding point in each eye, the mind is conscious of one 
 image. If we alter the direction of the axis of one eye by 
 pressing gently on that eye, an image is formed on a point 
 of the retina of that eye which does not correspond to 
 the point upon which the image falls in the other eye, and 
 consequently we squint, or see two images. 
 
 Questions. 
 
 224. Define the position of the blind spot, and prove that it exists. 
 
 225. Wliat is a short-sighted eye ? How may the defect be remedied ? 
 
 Draw diagrams showing the state of the eye in emmetropia (nor- 
 mal), myopia, and hypermetropia. 
 
 226. Explain the cause of musue ■volitantes. What are. phosgenes ? 
 
 227. 228. Show geometrically how an image is formed on the retina. 
 229. What is meant by the term ' corresponding points ? ' 
 
 Hearing. 
 
 230. General Description of Ear. — The organ of 
 hearing is composed of three portions, the external, middle, 
 and internal ear. The external ear consists of the auricle, 
 which presents elevations and depressions, the functions of 
 which are to receive and reflect the vibrations of the air 
 which constitute sound, and to transmit these by a tube, 
 partly cartilaginous, partly bony, called the auditory canal 
 (fig. 131, 15, 16), to the middle ear. The middle ear is named 
 the tympanum or drum, 21. It is a cavity in the petrous or 
 hard portion of the temporal bone. It is shut off from the 
 auditory canal by the membrane of the drum, i-i, a thin struc- 
 ture capable of vibrating when acted on by the vibrations of 
 the air. The tympanum communicates with the back of the 
 throat by the Eustachian tube, 23, the function of which is to 
 
THE SENSES. 205 
 
 equalise atmospheric pressure on both sides of the vibrating 
 membrane. When this tube becomes stopped mechani- 
 cally by enlargement of the tonsils, partial deafness is 
 the result, and when cleared so as again to allow air 
 to pass into the tympanum, hearing at once returns to 
 
 Fig. 131. — Diagram of the Ear ; natural size : 
 
 r, auditory nerve ; 2, internal auditory meatus closed by the cribriform plate of 
 bone through the perforations of which the branches of the auditory nerve pass 
 to the ear ; 3-8, membranous labyrinth composed of 3, utricle, 4, semicircular 
 canals, 5, saccule, 6, duct of the cochlea (the coils not entirely shown), 7, endo- 
 lymphatic duct with, 8,- its saccule lying inside of the cranial cavity ; 9, lymphatic 
 space surrounding the membranous labyrin-th ; 10, osseous labyrinth of compact 
 bone lying in the more spongy substance of the petrous bone, 11, 11 ', 12, the 
 oval window, filled by the foot-plate of the stirrup-bone ; 13, the round window, 
 across which is stretched the internal tympanic membrane; 14, auricle; 15, 16, 
 external auditory meatus ; 15, its cartilaginous, and, 16, its bony part ; 17, tym- 
 panic membrane; 10-20, auditory ossicles; 18, hammer; 19, anvil ; 20, stirrup; 
 21, middle ear; 22, osseous, and, 23, cartilaginous portion of the Eustachian 
 tube ; 24, cartilages of external auditory meatus. 
 
 its normal state. Stretching across the tympanum we find 
 a chain of small bones, one of which, the malleus^ or hammer 
 (figs. 131, 18, and 133, m), is attached by a long handle, 
 h, to the drum ; this unites by a joint with another, 
 the mcus, or anvil (figs. 131, 19. 132, and 133, sc^ k) ; 
 which in turn bears the stapes, or stirrup (figs. 131, 20, and 
 
2o6 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 133, s) ; the base of this is fixed to a small oval mem- 
 brane closing an aperture, the femstra ovalis, which 
 communicates with the internal ear (fig. 131, 12). The 
 function of this chain of bones, which is really a 
 
 Fig. 132.— Incus and Malleus of the 
 right side seen in their Natural Posi- 
 tion in the Tympanum : 
 
 I, tympanic membrane : 2, Eustachian tube ; 
 3j tensor tympani muscle seen attached to the 
 malleus ; 4, anterior ligament of the malleus 
 attached to the processus gracilis ; 5, superior 
 ligament of the malleus ; 6, chorda tympani 
 nerve ; rt, b, c, sinuses or spaces connected 
 with the tympanum in which the ossicles move 
 freely. ' 
 
 Fig. 133. — Ossicles of the 
 Left Ear as seen from the 
 outside and below : 
 
 »2, head of the malleus ; g, the 
 slender process, or processus 
 gracilis ; h, the manubrium or 
 handle ; sc, the short crus, and /c, 
 the long crus of the incus ; a, the 
 position of the lenticular process, 
 through the medium of which it 
 articulates with the head of the 
 stapes ; ^, the base of the stapes. 
 
 jointed lever, is to convey vibrations or minute variations 
 of pressure from the membrane to the internal ear. 
 
 231. Structure of Internal Ear.— The internal ear, or 
 labyrinth, so called on account of its complexity of structure, is 
 the essential part of the organ of hearing, because here we 
 find the filaments of the auditory nerve which are ultimately to 
 receive impulses originally produced by vibrations of the air, 
 and conveyed by the intermediate structures already described. 
 It is made up of three parts — the vestibule, or central part ; the 
 semicircular canals, three in number, which communicate by 
 
THE SENSES. 
 
 207 
 
 five openings with the vestibule ; and the cochlea, so called from 
 its resemblance to a snail shell (fig; 135). Each of these parts 
 is excavated from the sub- 
 stance of the bone, and forms 
 the bony or osseous labyrinth ; 
 but within this we have a fibrous 
 structure exactly correspond- 
 ing in shape, the membran- 
 ous labyrinth (fig. 134). The 
 osseous is separated from the 
 membranous labyrinth by a 
 fluid called the perilymph; and 
 within the membranous portion 
 there is another fluid known as 
 the endolymph. The termina- 
 tions of the auditory nerve end in vibratile structures in the 
 membranous portion ; and by the presence of the two fluids 
 
 Fig. 134. — Scheme of Mamma- 
 lian Labyrinth : 
 
 «, utrfcle : ^, saccule ; tr, aquseductiis 
 vestibuH, dividing into two branches, 
 going to saccule and utricle respec- 
 tively ; rf, canalis or ductus reuniens. 
 
 Fig. 135. — Interior of the Osseous Labyrinth : 
 V, vestibule : av^ aqueduct of the vestibule ; fl, fovea semi-elliptica ; r^ fovea 
 hemispherica. S, semicircular canals; j, superior: /, posterior; i, inferior; 
 tr, a, n, the ampullar extremity of each. C, the cochlea ; sv, osseous zone 
 of the lamina spiralis^ above which is the scala vestibuli, communicating with the 
 veslibtile ; sf, scala tympani, below the spiral lamina. 
 
 just mentioned, the most delicate pressures of the air com- 
 municated directly to the membrane of the drum and chain 
 
208 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 of bones, or indirectly through the bones of the head, are 
 conveyed to these vibratile structures, and by these to the 
 nerves. 
 
 232. Structure of Cochlea. — The structure of the coch- 
 lea is very remarkable. It consists of a central pillar, round 
 which a tube makes two and a half coils. This tube is divided 
 into two compartments by a partition, partly bony, partly 
 membranous (fig. 135, C, sv). The upper portion communi- 
 cates with the vestibule, and, from its fancied resemblance to 
 a stair, has been called scala vestibuli. Suppose we ascended 
 this stair to the apex of the cochlea, we would there find a 
 
 Fig. 136. 
 
 Section through one of the Coils of the Cochlea (diagrammatic) : 
 
 SV, scala vestibuli ; ST, scala tympani ; CC, canal of the cochlea ; IsOt lamina 
 spiralis ossea, or spiral plate of bone ; lls^ limbus of the spiral lamina ; R, 
 Reissner's membrane ; sSy spiral sulcus or groove : ^, tectorial membrane ; CO, 
 organ of Corti ; ^, basilar membrane ; &/, spiral ligament : «c, cochlear nerve ; 
 gs^ spiral ganglion in course of cochlear nerve. 
 
 small opening communicating with the lower compartment, 
 which has been called the scala tympani. It receives this name 
 because at the bottom it communicates with the tympanum by a 
 round opening, called the fenestra rotunda, closed by a thin 
 membrane (fig. 131, 10, 13). The cochlear branch of the 
 auditory nerve enters the base of the pillar just mentioned, 
 and distributes branches to the membranous portion of the 
 scalae. But this is not all. Between the two scalse or staircases, 
 
THE SENSES. 
 
 209 
 
 in a triangular space, there is a remarkable organ called 
 the organ of Corti (fig. 136, CO). This is a complicated 
 structure, consisting essentially of three or four thousand 
 
 Cells of Claudius. 
 ■Cells of Hcnsen,- ' 
 
 Outer hair 
 cells. 
 
 Phalanges. 
 Outer head plate. 
 Inner head plate. 
 Inner hair cells. 
 
 Epithelium of 
 ' ^ sulcus spiralis. 
 
 Awiitorii teeth. — 
 
 « 
 
 Fig. 137.— The Organ of Corti. 
 
 A, seen in transverse section ; B, seen from above ; very highly magnified. The 
 two views are placed side by side, and the names between apply to the 
 view on each side. Note, by a study of fig. 136, where the organ is situated 
 (CO). 
 
 jointed rods, supporting ciliated cells called hair-cells, which 
 are apparently capable of vibrating. These are connected 
 with auditory nerve filaments (see figs. 131, i, 136, nc, and 
 137, A, nerves. 
 
 233. Functions of Parts of Ear. — We know little 
 
 N 
 
2IO ELEMENTARY HUMAN PHYSIOLOGY. 
 
 regarding the functions of the different parts of the internal 
 ear. That they have different functions we infer from the 
 structure being so dissimilar, and also from the facts of 
 comparative anatomy. In the animal kingdom, the vesti- 
 bule first appears ; to this are superadded the semicircular 
 canals ; and, lastly, the cochlea, which increases in ' com- 
 plexity from the lower orders of the mammalia up to man, 
 in whom it is one of the most complicated organs of the 
 body. The vestibule probably enables us to experience a 
 sensation of sound as such ; the semicircular canals may 
 assist in determining the direction of sounds, or, according 
 to recent researches, may so affect us as to give us the 
 sense of equilibrium or of rotation ; while there are many 
 arguments in favour of the view that the cochlea, as we find 
 it in man, with a highly elaborated organ of Corti, may 
 be the mechanism by which we appreciate the fitch and 
 quality of musical sounds, which act so powerfully in 
 exciting the emotions. 
 
 234. Range of Hearing. — The range of hearing, like that 
 of vision, varies in different persons. Some are insensible to 
 sounds that others hear. Many cannot hear the chirp of a 
 grasshopper or the squeak of a bat, two of the shrillest sounds 
 produced by living beings. The range of the ear is much 
 greater than that of the eye in detecting movements which 
 produce vibrations. Thus we hear the sound produced by a 
 vibrating rod or string long after we have ceased to see the 
 movements. The range of the human ear is about eleven 
 octaves. The lowest sound recognisable as musical is pro- 
 duced by about 32, and the highest by about 32,000 vibrations 
 per second. 
 
 Questions. 
 
 230. Where is the drumhead of the ear situated? What is the 
 
 tympanum ? How does the tympanum communicate with the 
 external air ? . Describe the chain of bones. 
 
 231. What are the parts of the labyrinth? How are pressures com- 
 
 municated from the drumhead to the labyrinth ? 
 
THE SENSES. 211 
 
 232. What is the cochlea? Draw a diagram showing a section 
 
 through the tube of the cochlea. Where is the organ of 
 Corti ? 
 
 233. What uses have been assigned to the semicircular canals ? 
 
 234. What is a vibration ? What is the range of the ear as regards 
 
 the appreciation of vibrations ? 
 
 The Muscular Sense. 
 235. There is still another sense, called the muscular 
 sense, or sense of weight. If we close our eyes, and hold 
 a weight on the palm of the outstretched hand, we experi- 
 ence a peculiar sensation. It is not referable to any of the 
 five senses, except, perhaps, to touch. But it is not simple 
 touch. We are conscious of an effort to sustain the weight, 
 and of a firm condition of the muscles of the arm. This 
 sensation is the muscular sense. It is the sensation we 
 experience when any groups of the voluntary muscles are 
 called into action, and by it we become aware of the con- 
 dition of these muscles. By means of this sense, we stand 
 erect, we walk, balance ourselves on a narrow ledge, throw 
 stones or weapons, play on many instruments, &c. ;" and it 
 adds largely to our feelings of pleasure. It is chiefly by 
 means of the muscular sense that we receive our notions 
 of solidity, relief, and of things being external to, and at a 
 certain distance from, ourselves (fig. 156). 
 
 Question. 
 
 235. Prove the existence of a muscular sense. 
 
 CHAPTER XIV. 
 
 THE NERVOUS SYSTEM. 
 
 236. General Description of Nervous System. — 
 The vital processes already described (with the exception 
 of those connected with the senses) belong to the class 
 
212 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 of functions known as vegetative, because certain of them 
 are common to vegetables as well as to animals. These 
 functions have as their object the preservation of the plant. 
 The animal has, however, another set of organs, by the use 
 of which it becomes conscious of a world external to itself, 
 and by which, as stated above, a control, both stimulating 
 and regulative, is exercised over the other organs. By 
 means of certain functions, which, from their occurrence in 
 animals only, are termed animal, all the higher animals, 
 and especially man, are endowed with sensation, motion, 
 and volition. These powers are due to the presence of a 
 nervous system, including two sets of nerves and nerve- 
 centres — namely, the cerebrospinal system and the sym- 
 pathetic system (see p. 38). 
 
 The former consists of the cerebrospinal axis, composed 
 of the brain and spinal cord, and the cerebral and spinal 
 nerves connected with this axis ; while the latter consists 
 chiefly of a double chain of ganglia or nervous masses, 
 lying at the sides of the spinal column, and united with one 
 another and with the spinal nerves by connecting threads 
 of nervous substance (fig. 154). 
 
 237. Characters of Nervous Matter to the Naked 
 Eye. — Nerve matter is of two kinds, white and gray, which 
 may be readily seen by cutting through the brain of a 
 sheep or of any other animal, when it will be observed that 
 there is an outer layer of gray matter, while the interior is 
 white. In the spinal cord these relations are reversed, the 
 gray matter lying in the centre. 
 
 238. Structure of Nerves. — These consist of a 
 number of delicate fibres, each of which is transparent as 
 glass when examined in a perfectly fresh state, but usually 
 seen with two well-defined lines on each side of a broad 
 clear space. The central part is called the axis-cylinder, 
 and the outer part, the white substance of Schwann. Very 
 minute nerve-fibres, such as those obtained near the surface 
 
THE NERVOUS SYSTEM. 213 
 
 of the brain (fig. 138, f,/), show no white substance. The 
 nerve-fibres vary much in diameter. Those of the sym- 
 pathetic have no white substance. At certain distances 
 the white substance is interrupted, while the axis-cylinder 
 is continuous, constituting the so-called 7iodes of Ranvier, 
 During life the substance in the interior of the sheath of 
 
 a b 
 
 Fig. 138.— Nerve-fibres. 
 
 c, ordinary-sized nerve-fibre showing axis-cylinder 
 surrounded by white substance ; d^ smaller 
 nerve-fibre, with white substance scarcely 
 visible ; e^ still smaller, with no white substance 
 visible; f^ varicose nerve-fibre, from gray matter 
 near surface of brain; rt, nerve-fibre, coloured 
 and acted on by ostnic acid, showing one of 
 the nodes of Ranvier, or complete interruption 
 of the white substance with continuity of the 
 axis-cylinder ; b, nerve-fibre showing nucleus 
 and node of Ranvier (the axis-cylinder is 
 blackened) ; g^ non-medullated nerve-fibre from 
 sympathetic, having no white substance, and 
 nucleated at intervals. 
 
 Fig. 139. 
 Transverse Section of 
 Nerve : 
 To the left is seen a portion of a 
 section of a nerve. Observe 
 the partitions of connective 
 tissue that separate groups of 
 nerve-fibres from each other. 
 The nerve-fibres seen cut trans- 
 versely vary in diameter. A 
 section of a single fibre is seen 
 to the right : a, neurilemma, or 
 Schwann's sheath ; ^, axis- 
 cylinder ; dt white substance. 
 
 the nerve-fibre (the neurilemma) is in a semifluid state, and 
 the conception of a nerve-fibre to be formed is, a thin 
 cylinder {neurilemma) enclosing a cylinder of semifluid 
 substance {white substance of Schwann), within which there 
 is a core of semifluid matter, of different consistence from 
 the last, called the axis-cylinder (fig. 139). 
 
 239. Nerve-cells. — When nerve-fibres are traced into 
 the nerve-centres, they are found to terminate in nerve-cells, 
 which are of various forms. These cells are composed of 
 
214 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 protoplasmic matter, slightly molecular, and usually having 
 issuing from them one or more poles or processes. One 
 
 Fig. 140. — Various forms of Nerve-cells. 
 u, multipolar^ from gray matter of spinal cord : 3, rf, bipolar^ from ganglia on 
 posterior roots of spinal nerves ; f, g^ unipolar, from cerebellum ; g, shows 
 indications of a process coming off at lower end ; £, union of three multipolar i 
 cells in spinal cord ; f, union of three tripolar cells in gray matter of cerebral 
 hemispheres. Nerve-cells are probably never connected, as shown in e 3.T1A/. All 
 the processes, with the exception of the one giving origin to an axis-cylinder, 
 break up into extremely fine fibres, or, as now called, an arborisation, like the 
 twigs of a tree (fig. 141, a.p.). 
 
 large process issuing from a cell is in continuation with the 
 axis-cylinder of a nerve-fibre (fig. 141, a.p.). They vary 
 in size from the jinnrth to the 
 j^th of an inch. The function 
 of these cells is to receive or 
 transmit nervous impulses, but 
 how they do so is quite un- 
 known. Gray matter is com- 
 posed chiefly of these cells 
 lying amongst extremely deli- 
 cate connective tissue termed 
 neuroglia. 
 
 240. Functions of a Nerve- 
 fibre. — The function of the 
 an impression of any kind — 
 mechanical, chemical, thermal, electrical, or volitional — 
 
 a.p. 
 
 Fig. 141. 
 
 Nerve-cell from Spinal Cord: 
 
 a.p., axis-cylinder process. 
 
 nerve-fibre is to receive 
 
THE NERVOUS SYSTEM. 215 
 
 thereupon to generate an influence, and to conduct this 
 influence to or from a nerve-centre. The rapidity of the 
 nerve-impulse is, in cold-blooded animals, from 75 to 120 
 feet per second ; incomparably slower than light or elec- 
 tricity. In warm-blooded animals, such as man, it travels 
 at a rate of about 200 feet per second. 
 
 Questions. 
 
 236. Compare the central nervous system with the sympathetic 
 
 system. 
 
 237. When you cut into the brain or spinal cord, what kinds of matter 
 
 may be seen ? 
 
 238. Describe the structure of a meduUated nerve-fibre. 
 
 239. Draw a diagram showing the various kinds of nerve-cells. 
 
 240. What are the chief functions of a nerve-fibre ? What is the rate 
 
 at which an impulse is transmitted along a nerve ? 
 
 THE DEVELOPMENT OF THE NERVOUS SYSTEM IN THE 
 ANIMAL KINGDOM. 
 
 241. Nothing conduces sooner to an intelligent comprehen- 
 sion of the complicated nervous system of man and of the 
 higher animals than the study of the gradual development 
 of the nervous system throughout the animal kingdom, from 
 its simpler to its more complex forms. Suppose the surface of 
 an animal's body to be covered with epithelium cells, as in fig. 
 142, c, one of these is by-and-by set aside for the reception of 
 a special stimulus, such as pressure, or light, or sound. A 
 process (the beginning of a nerve) passes from this cell to 
 another cell situated deep in the tissues of the animal, but 
 without actual continuity at a, and this cell (the beginning of 
 a central nervous system) acts on the muscular fibre 6, causing 
 contraction or movement. A stimulus applied to ci caused 
 movement ofd. 
 
 A still more complicated arrangement is seen in fig. 143. 
 Here a nerve-cell / in the brain acts through the fibre e oh 
 the cell c, situated, say, in the spinal cord (but not continuous 
 with it), and c, in its turn, acts on the muscle-fibre a, by 
 the nerve-fibre d. From e, fibres ei and d pass off, so that a 
 
2l6 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 Stimulus Starting at/ may initiate movements in many muscle- 
 fibres by such offsets as d and d. 
 
 Fig. 142. — Simple plan 
 of nervous mechanism as 
 in lower forms of life. 
 
 Fig. 143. — Complicated plan of 
 nervous mechanism, causing move- 
 ment, as in higher animals. 
 
 242. Nervous System of Invertebrates. — In none of 
 the Protozoa, including such animals as sponges, infusoria, &c., 
 
 ®' 
 
 Fig. 144. — Nervous Fig. 145. — Nervous 
 System oi&Serpula System of an Ant : 
 or Seaworm : a, cephalic ganglion. 
 
 a, cephalic ganglion. 
 
 Fig. 146. — Nervous 
 System of a Crab : 
 
 a, cephalic ganglion ; b, 
 mass of ventral ganglia 
 fused together. 
 
 has any trace of a nervous system been discovered. Neither 
 is any rudiment of it to be found in the Hydrozoa, the first 
 subdivision of the ccelenterate group of animals ; but in the 
 
THE NERVOUS SYSTEM. 
 
 217 
 
 Actinosoa, which comprehends such animals as the sea- 
 anemone, it is first discovered as a little knot or nodule of 
 nervous matter, from which delicate fibres radiate. Such a 
 nodule is called a ganglion, and the filaments constitute nerves. 
 Among the Echinodermata, such as starfishes, sea-urchins, 
 &c., we find the nervous system consisting of a number of 
 ganglia, connected together, so as to form a ring, or nervous 
 circle, from which nerve-filaments pass to various parts of the 
 body. In some of the Annelida, or worms, we find (fig. 144) 
 a ganglion, a, in the neighbourhood of the head, from which 
 two nervous cords pass along the ventral (or belly) surface of 
 the animal. In the Mollusca, or shellfish, there are usually at 
 least three ganglia with radiating nerves— one in the head, one 
 in the foot, and one posterior and above the alimentary canal. 
 In the Insecta, or insects (fig. 145), we find a large ganglion in 
 the head, a, from which a double cord passes backward along 
 the ventral surface of the animal, and in.connection with which 
 there are three or more ganglia, as seen in the figure. In the 
 Crustacea, such as the common crab 
 (fig. 146), there is a large ganglion near 
 the anterior extremity, with nerves for 
 the eyes and antennae, a, while behind 
 we find the ventral chain of ganglia 
 fused into one mass, b. 
 
 243. Nervous System of Verte- 
 brates.— All of the groups now men- 
 tioned belong to the invertebrate sub- 
 division of the animal kingdom, and 
 all have their nervous system along the 
 ventral aspect of the body. We now 
 come to the vertebrate subdivision, or 
 those having a backbone, and here we 
 meet with another nervous system ex- 
 tending along the dorsal aspect of the 
 animal, to which anatomists have given 
 the name of the cerebrospinal system, 
 chain of ganglia constituting the brain, 
 an elongated mass of nervous matter, running from the bram 
 through the canal of the vertebral column, called the spinal 
 
 Fig. 147. 
 Diagram of an Ideal or 
 
 Typical Brain : 
 J, olfactory lobes; 2, cere- 
 brum ; 3, corpus stria- 
 tum ; 4, optic thalamus ; 
 5, cerebellum ; 6, pons 
 Varolii ; 7, medulla ob- 
 longata ; 8, spinal cord. 
 
 This consists of a 
 behind which there is 
 
2l8 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 cord, or spinal marrow. In all vertebrate animals, the spinal 
 marrow seems to be much alike in general structure and arrange- 
 ments (although the spinal cord of a man is a more ' com- 
 plicated organ than that of a rabbit), but one animal differs 
 from another (as a fish from a frog, or a pigeon from a rabbit) 
 mainly in the degree of development of the brain. The brain 
 consists of a series of ganglia which, in a typical or ideal brain, 
 might be thus represented (fig. 147). These ganglia, from 
 before backwards, are : i, olfactory lobes ; 2, cerebral lobes ; 
 3, corpora striata ; 4, optic thalami ; 5, cerebellum ; 6, pons 
 Varolii ; 7, medulla oblongata ; and 8, spinal cord. Between 
 4 and s we also find a mass of nervous matter termed the 
 optic lobe or lobes. 
 
 Such a brain is seen, for example, in many fishes (fig. 148), 
 
 Fig. 148. 
 
 Brain of Common 
 
 Gurnard : 
 
 , olfactory; 2, cerebral 
 lobes ; 3, corpora striata ; 
 4, cerebellum. 
 
 Fig. 149. 
 
 Brain of Common 
 
 Frog: 
 
 (j olfactory ; b, cerebral 
 lobes covering corpora 
 striata ; c, corpora quad- 
 rigeniina, or optic lobes ; 
 dt cerebellum (rudiment- 
 ary) : J, back of medulla 
 showing fossa. 
 
 Fig. 150. 
 
 Brain of Tortoise : 
 
 , olfactory; 2, cerebral 
 lobes ; 3, corpoi-a striata ; 
 4, optic lobes; iv, cere- 
 bellum ; 5, medulla. 
 Part of the surface of 
 the cerebral lobes has 
 been removed to show 
 the cavities in the in- 
 terior termed the ventri- 
 cles. 
 
 where the cerebral hemispheres, 2, are still of very small 
 size, and do not overlap any of the adjacent structures. 
 The same arrangement may also be studied in the brain 
 
THE NERVOUS SYSTEM. 
 
 219 
 
 of amphibians, such as the common frog (fig. 149) ; but 
 here we find the cerebral lobes larger, so that they now ex- 
 tend backwards so as to cover 
 the corpora striata. When ^ 
 we ascend to reptiles, such 
 as the tortoise (fig. 150), we 
 find the cerebral hemispheres 
 larger, broader, and thicker 
 as regards the amount of 
 gray nervous matter on the ^^S- 151.— Brain of Pigeon : 
 
 surface. The cerebellum is ^' ^"^^ fro-n above. B, lateral view of 
 
 a bisected brain. A : «, olfactory ; o, 
 
 still feebly developed. In the cerebral lobes ; c, optic lobes ; d, cere- 
 brain of birds the cerebral bellum ; «, medulla. B ; «, cerebrum ; ^, 
 lobes are Stillfurther developed cerebellum ; c, olfactory ; d, optic nerves ; 
 
 (fig. 151), and the cerebellum *■' ""^ " * ■ 1 "^or . 
 has become so large as to wedge in between the two optic 
 lobes and push these towards the base of the brain. The 
 mammalian brain shows the hemispheres of the cerebrum still 
 larger, so that they now project so far posteriorly as to 
 
 Fig. 152. — Brain of Rabbit : Fig. 153. — Brain of Common 
 
 I, olfactory ; ^, surface of cerebral Ca,t, showing Convoluted Sur- 
 
 hemisphere ; 3, cavity in brain face, 
 
 called a lieniriclsy in the floor of 
 which is seen the corpus striahtm ; 
 4, cerebellum. 
 
 cover not only the corpora striata and optic thalami, but 
 also the optic lobes. The cerebellum is also much more 
 highly developed. The brains of the lower mammals, such 
 as the rabbit (fig. 152), are nearly smooth on the surface, 
 and exhibit only a. trace of those elevations and depressions 
 
220 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 which we meet with on the surface of the brains of such an 
 
 animal as the common 
 cat (fig. 153), where 
 we find the surface 
 distinctly convoluted. 
 The convolutions in- 
 crease in number, 
 depth, and complexity 
 as the intelligence of 
 the animal increases, 
 until we come to the 
 brain of man, where 
 in a well-developed 
 brain we find them 
 presenting the appear- 
 ance depicted in (figs. 
 155 and 156). It will 
 thus be seen that as 
 we ascend from the 
 lower to the higher 
 vertebrates, the brain 
 becomes more and 
 more complex in struc- 
 ture, chiefly by the 
 great growth and de- 
 velopment backwards, 
 of the cerebral hemis- 
 pheres, and by the 
 appearance of con- 
 
 «, cerebrum ; b, cerebellum ; c, medulla oblongata ; volutions on the Sur- 
 d^ spinal cord, from which the spinal nerves arise ; face of these, indicat- 
 ..brachial plexus; /sciatic nerve. j^^g increase of gray 
 
 matter. The general plan of the nervous system in man is 
 shown in fig. 154. 
 
 Fig. 154. 
 
 Questions. 
 
 241. Describe the simplest form of nervous system. 
 
 242. Show how the nervous system gradually, becomes complicated in 
 
 invertebrate animals. 
 
THE NERVOUS SYSTEM. 
 
 221 
 
 243. Draw a diagram showing the parts in the typical brain of a 
 vertebrate animal. Compare the brains of a fish, a frog, and a 
 tortoise. Describe the brain of a bird. Compare the brains of 
 a rabbit and a cat. How do the brains of the lower mammalia 
 differ in general from the brain of a man ? 
 
 THE HUMAN BRAIN. 
 
 244. General Description. — The brain consists of the 
 
 Fig. 155. — Under Surface, or Base of Brain : 
 F.L., T.L., O.L., frontal, temporal, and occipital lobes of the cerebrum; cbt ch, 
 cerebellum, the medulla oblongata lying between its two lobes. Cranial Nerves. 
 — I. olfactory lobe (the nerve of smell) ; 2, optic nerve (nerve of sight) ; 3, third 
 or oCulo-motor nerve, motor nerve to most of the muscles' of the eye ; 4, fourth or 
 trochlear nerve, motor nerve to the superior oblique muscle of the eye ; 5, fifth, 
 trigeminus, or trifacial, sensory and motor, the large root sensory to the face and 
 eyes, &c. ; the small root, motor to muscles of mastication ; 6, sixth or abducens 
 nerve, to external rectus muscle of eye, turns eyeball outwards ; 7, seventh or 
 facial, motor to muscles of expression ; 8, eighth or auditory nerve, sensory for 
 hearing (cochlea) and for equilibration (semicircular canals] ; g, glosso- pharyngeal, 
 sensory nerve of taste, and motor to some of the muscles of deglutition ; 10, 
 pneumogastric, sensory and motor to larynx, lung, heart, and stomach ; 11, spinal 
 accessory, motor to muscles of heart (inhibitory) and sterno-mastoid and trape- 
 zius ; 12, hypoglossal, motor to all the muscles of the tongue ; cj, first cervical 
 spinal nerve. 
 
 cerebrum, or brain proper, which occupies the whole of the 
 
ELEMENTARY HUMAN PHYSIOLOGY. 
 
 upperand front parts of the cavityof the skull; the. cerebellum, 
 or little brain, lying beneath the hinder part of the cerebrum : 
 and the medulla oblongata, or oblong marrow, which may 
 be regarded as a continuation of the spinal cord within the 
 cavity of the cranium, and as forming the connection be- 
 tween the brain and cord. The cerebrum and cerebellum 
 are almost completely divided into two lateral halves by a 
 deep median longitudinal fissure ; and the surface of the for- 
 mer is indented by a considerable number of tortuous fur- 
 rows, nearly an inch 
 deep, mio convolutions. 
 As the gray matter is 
 extended into these 
 furrows, its quantity 
 is thus vastly in- 
 creased (see figs. 155, 
 156, and 157). 
 
 At the base of 
 the cerebrum, and 
 connected with it, 
 are two large gang- 
 lionic masses of gray 
 and white matter, 
 called the corpora 
 striata; behind these, 
 other two bodies of a 
 similar nature, the 
 optic thalami ; and 
 still farther back, four 
 bodies, two on each 
 side, \ht corpora guad- 
 rigemina. All these 
 parts of the brain are 
 connected with each other by numerous nerve-fibres. The 
 fibres from the spinal cord pass upwards in the medulla 
 
 Cerebrum- 
 To show, firstly, 
 
 Fig. 156. 
 
 upper surface (Quain) : 
 division into two nearly equal 
 hemispheres by the great median fissure ; 
 secondly, general appear.ince and apparent 
 irregularity of arrangement of the convolutions 
 and fissures ; F.L., frontal lobe; O.L., occipital 
 lobe. 
 
THE NERVOUS SYSTEM. 223 
 
 oblongata; those from the posterior parts of the cord going 
 chiefly to the cerebellum, while those from the anterior 
 parts pass chiefly to the cerebrum. In the cerebrum, 
 cerebellum, and ganglia we also find fibres running from 
 their anterior to their posterior ends, while other fibres run 
 transversely, and unite corresponding parts on opposite 
 sides of the brain (fig. 157, corpus callosum). Thus there 
 is evidently community of function. 
 
 245. Functions of different Parts of the Brain. 
 — The functions of these different parts may be briefly 
 stated to be as follows : (i) the cerebrum is the seat of 
 sensation, volition, emotion, of those intellectual powers. 
 
 Fig. 157. — Vertical Section of Brain. 
 
 n, a, cerebrum and convolutions ; b, optic thalamus ; t, corpora quadrigemina ; 
 
 d, section of cerebellum ; e, optic nerve ; /^ pons Varolii ; ^, medulla oblongata. 
 
 in short, which constitute Mind ; (2) the cerebellum is the 
 chief regulator of muscular movements ; (3) the corpora 
 striata are great centres of voluntary movement, not of 
 volition, but of the nervous mechanism by which, when we 
 will by means of the cerebrum, the influences are sent along 
 the spinal cord to the various muscles; (4) the optic thalami 
 collect and transmit tactile (touch) impressions coming 
 
2 24 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 from all parts of the body which excite sensation ; (5) the 
 corpora quadrigemina receive impressions by the optic 
 nerves from the eyes, and transmit these to the cerebrum, 
 where there is then the consciousness of sight ; and (6) the 
 medulla oblongata, and an adjoining part called the pons 
 Varolii, are the seat of the nervous influences which 
 regulate swallowing, breathing, and other important in- 
 voluntary movements. The parts of the brain last men- 
 tioned (6) are absolutely essential to life. The other parts 
 may be cut or mutilated without instant death, but this 
 quickly follows injury to the medulla. 
 
 246. Motor Areas. — Observations made on the cerebral 
 hemispheres by stimulating small areas on their surface by 
 feeble electric currents, have led to the discovery of certain 
 'centres' in the convolutions which, when stimulated, cause 
 movements of definite groups of muscles. These centres have 
 been termed motor-ce.rAx^%. There is thus a centre in the 
 cortex of the brain for each muscle and group of muscles. 
 Each centre probably receives sensory impulses from skin or 
 mucous membrane, or from other centres in the brain itself, 
 which impulses in turn stimulate the centre so as to cause 
 movements of specific groups of muscles. 
 
 247. Functions of Nerves. — Nerves have different 
 functions. When an influence travels along a nerve to a 
 muscle, it excites the muscle to contract, and the former is 
 then called a motor nerve ; when it travels to the brain and 
 causes a sensation, we call such a nerve sensory. A third 
 class of nerves, when stimulated, convey impressions to 
 glands, and the consequence is secretion. There is no evi- 
 dence that there is any difference of structure between motor 
 and sensory nerves. The difference of result on stimulating 
 a nerve depends on its mode of termination. For example, 
 if it terminate in the hemispheres of the brain, sensation 
 or pain is felt ; if in a muscle, the result is contraction ; if 
 in a gland, the secretion is augmented or diminished ; if in 
 a blood-vessel, the vessel may contract or dilate. Most 
 
THE NERVOUS SYSTEM. 
 
 225 
 
 nerves contain both sensory and motor fibres. Some are 
 purely sensory, as certain parts of the fifth cranial nerve ; 
 others purely motor, as the facial, or seventh cranial nerve ; 
 while all the spinal nerves have both sensory and motor 
 fibres. Certain nerves respond only to particular stimuli. 
 For example, the optic nerve is affected only by vibra- 
 tions of rays of light, acting in the first instance on a special 
 terminal apparatus called the retina. Such are called special 
 sensory nerves, and include those of sight, hearing, taste, 
 smell. The nerves of touch are those of common sensi- 
 bility distributed to the skin (see also pages 73 to 76). 
 248. Cranial and Spinal Nerves. — Twelve pairs of 
 
 Fig. 158. — Diagram of the 
 Brain, sliowing origin of 
 the cranial nerves : 
 
 H, hemispheres ; CS, corpora 
 striata ; P, pineal gland ; CQ, 
 corpora quadrigemina ; TH, 
 optic thalami ; PT, pituitary 
 body ; M, medulla. The 
 Roman numerals indicate the 
 nerves. Sp, i, Sp. 2, first and 
 second spinal nerves. Observe 
 the ganglia on the posterior 
 roots. 
 
 nerves are given off from the brain, and thirty-one from the 
 spinal cord. The spinal nerves are all sensori-motor — that 
 is, they contain both kinds of filaments. The cranial 
 nerves may be thus classified, and their general origin may 
 be studied in figs. 155 and 158 : 
 
 Order. 
 
 1st Pair. 
 2d Pair. 
 3d Pair. 
 
 Physiological 
 Name. 
 
 Function. 
 
 Anatomical Name. 
 
 .Olfactory, I Olfactory Special sense, smell. 
 
 . Optic, II Optic Special sense, sight. 
 
 .Motor-oculi, III.. Motor-oculi.. Motor, for all the muscles of the 
 
 eyeball except two, IV. and VI. 
 O 
 
226 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 Order. Anatomical Name, ^^'"^'"^f'^^ Function. 
 
 4th Pair . . . Trochlear, I V. ., . . Pathetic Motor for superior oblique muscle 
 
 of eyeball. 
 5th Pair... Trigeminal, or 5th Nerve.... Sensori-motor—j^arorj' to face, 
 Trifacial, V. mouth, and part of tongue; 
 
 7?;0^0rto muscles of mastication. 
 6th Pair...Abducens, VI. ...6th Nerve .... Motor to external rectus muscle 
 
 of eyeball. 
 
 (Portio dura Facial "j Two portions— ^««/, the motor 
 ' nerve of the face; and the 
 Portio mollis Auditory... f „„rf;to^ _ special sense of 
 VII., VIII. J hearing. 
 
 8th Pair.. .8th 8th Three distinct nerves : (i) The 
 
 glosso-pharyngeal^ IX., special 
 sense of taste ; (2] the spinal 
 accessory, XI., motor to tra- 
 pezius muscle in back, sterno- 
 cleido-mastoid muscle in neck, 
 and motor filaments to pneumo- 
 gastric ; {3) the pnewnogastric 
 or vaguSy X., which extends 
 through the cavity of the chest 
 to the upper part of the abdo- 
 men— sensory and motor to phar- 
 ynx, oesophagus, larynx, lungs, 
 heart, and stomach ; inhibitory 
 to heart ; depressor to vaso- 
 motor centre in the medulla. 
 
 9th Pair... Hypoglossal. Hypoglossal, Motor to muscles of tongue. 
 
 XII. 
 
 Questions. 
 
 244. Describe what is seen on the under surface of a human brain. 
 
 What is the appearance of the upper surface of a human brain? 
 
 245. Suppose a human brain is divided into two parts by cutting 
 
 through the great median fissure : what may be seen ? Where 
 are the following parts : cerebrum, cerebellum, corpus striatum, 
 thalamus opticus, corpora quadrigemina, pons, and medulla ? 
 
 246. What is meant by the term ' motor area ' of the cortex ? 
 
 247. What are the various kinds of nerves in the body, considered 
 
 physiologically ? 
 
 248. Draw a diagram showing the relative positions, from before back- 
 
 wards, of the cranial nerves. What are the nerves of the eyes, 
 ears, tongue, nose? What is the motor nerve of the face? 
 What is the nerve of the face affected in neuralgia? What 
 nerve supplies the lungs, heart, and stomach ? 
 
THE NERVOUS SYSTEM. 
 
 227 
 
 THE SPINAL CORD. 
 
 249. The Spinal cord or marrow is a cylindrical column 
 of soft nervous tissue, extending 
 from the base of the skull, 
 where it is continuous with thea-| 
 viedulla oblongata, to the region 
 of the, loins, where it tapers ofTi-j 
 to a thread in the lowest part of ^ 
 the vertebral canal (figs. 159 and 
 162). Its average length is 
 eighteen inches. It is not only 
 divided by two fissures in therf-j 
 middle, but each half is again 
 divided longitudinally into three 
 equal parts by two parallel series 
 of nervous filaments, which are 
 the anterior and posterior roots 
 of the spinal nerves (figs. 160 and 
 161). The posterior root pre- 
 sents a swelling or ganglion, 
 immediately beyond which the 
 two coalesce into the trunk of a 
 nerve which, after emerging 
 through a hole called the inter- 
 vertebral foramen, is distributed 
 into branches to the parts it is 
 
 destined to supply with nervous Fig. 159.-Diagrammatic View 
 J-, . r 1 ii of Brain and Spinal Cord : 
 
 filaments ; as, for example, the , ^ 
 
 . rt, cerebrum ; by medulla oblongata ; 
 
 muscles of the trunk and limbs c, cerebellum ; d, spinal cord ; e, 
 
 and the surface of the body ^p;"^' "^oi^mn; /, cut ends of 
 
 //•-■•-# \ rrti 1 spinal nerves. 
 
 (fig. 154). These roots have 
 
 separate functions, the anterior being composed of motor, 
 while the posterior contain sensory fibres. Hence if the 
 anterior root be divided, or if the column of the cord 
 
228 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 from which it springs be diseased, loss of motion in the 
 part which it suppHes is the result, while if the posterior 
 
 root were similarly 
 acted on, there would 
 be loss of sensibility. 
 The anterior columns 
 of the medulla decus- 
 sate (that is, send 
 nerve-fibres across 
 to the adjoining 
 column) ; while the 
 fibres of the posterior 
 columns decussate 
 
 *■ t— . 
 
 Fig. 160. — Diagram of a segment of the 
 
 spinal cord, with a spinal nerve on each 
 
 side. 
 Observe the crescent-formed gray matter in the 
 
 cord surrounded by the columns of white matter. 
 
 On the right side the anterior (motor) root has 
 
 been cut Observe the ganglion or swelling on 
 
 the posterior (sensory) root. 
 
 higher up, near the upper part of the medulla oblongata. 
 
 Consequently all the motor 
 impulses starting, say, in the 
 right hemisphere of the cere- 
 brum excite muscular move- 
 ments on the left side of the 
 body and vice versa, because 
 all motor impulses cross over, 
 chiefly in the medulla, and 
 partly in the cord itself. 
 Again, all sensory impulses 
 from the left side of the body 
 find their way to the right 
 side of the brain, and vice 
 versd,, because all sensory 
 impulses cross over, chiefly 
 in the medulla. A clot of 
 blood therefore in the right 
 hemisphere of the brain will 
 cause paralysis both of motion 
 and sensation on the left side 
 
 of the body, while a similar injury to the left hemisphere 
 
 Fig. 161.— Side View ofj the 
 Spinal Cord, showing ' the 
 Fissures and Columns : 
 
 J, anterior median fissure ; 2, posterior 
 median jissure ; 3, anterior lateral 
 fissure ; 4, posterior lateral fissure ; 5, 
 lateral column ; 6, anterior column ; 
 7, posterior column ; 8, posterior 
 median column ; g, anterior root ; 10, 
 posterior root ; and 11, ganglion of 
 (12) a spinal nerve. 
 
THE NERVOUS SYSTEM. 
 
 229 
 
 will cause paralysis both of motion and sensation on the 
 right side. 
 
 Fig. 162. — Diagram showing the 
 close relation between the cerebro- 
 spinal and sympathetic systems. 
 
 Parts of the brain and medulla are seen at 
 the upper end, and the spinal cord is 
 traced downwards. Observe the spinal 
 nerves issuing from the sides of the cord 
 and forming plexuses or networks, from 
 which issue the great nerves going to the 
 limbs, as at 6, 7, 8, 9, 10 above, and at 
 the lower end, i, 2, 3, 4. The cord of the 
 sympathetic is seen on the left side. 
 Observe the ganglia a, b, c, d, and the 
 connections of these ganglia with the 
 anterior roots of the spinal nerves. All 
 the fibres of the sympathetic system 
 originally come from the cerebro-spinal 
 system. 
 
 *=ii»» 
 
 The spinal cord is not only a great conductor of motor 
 and sensory impulses : it also contains numerous centres 
 
 for reflex action. 
 
 Questions. 
 
 249. How is the spinal cord connected with the brain? Describe the 
 general arrangement of the spinal cord. What are the functions 
 of the roots of the spinal nerves ? Describe and explain the 
 effects of a severe injury of the right hemisphere of the brain. 
 
230. ELEMENTARY HUMAN PHYSIOLOGY. 
 
 SYMPATHETIC SYSTEM OF NERVES. 
 
 250. This nervous system consists of a ganglionated cord 
 found on each side of the spinal column, and giving to and 
 receiving numerous filaments from the cerebro-spinal sys- 
 tem (fig. 162 and description). Observation and experi- 
 ment have shown that it has the following functions : 
 (i) it controls the contractions of all structures which con- 
 tain involuntary muscular fibre, such as the viscera ; (2) it 
 governs the various secretions, probably by acting on the 
 blood-vessels of the glands ; and (3) it is vaso-motor, con- 
 trolling the calibre of the blood-vessels, and thereby 
 regulating the circulation in the capillaries, the blood 
 pressure in the greater arteries, and the distribution of 
 animal heat. The general relations of the sympathetic 
 system are seen in fig. 163. 
 
 Questions. 
 
 250. Where is the sympathetic system of nerves situated ? How is the 
 'sympathetic system connected with the cerebro-spinal system ? 
 What are the general functions of the sympathetic system ? 
 
 CHAPTER XV. 
 VOICE AND SPEECH. 
 
 251. There is a difference between voice and speech. 
 Voice is a sound produced by vibrations of two thin folds 
 of membrane called the vocal cords,' placed in the larynx, 
 at the top of the trachea or windpipe ; speech is the modi- 
 fication of voice into sounds connected with certain ideas 
 produced by the action of the brain, which we wish to 
 communicate to our fellow-men. Many animals have voice ; 
 none, except man, have articulate speech expressive of 
 
231 
 
 Fig, 163. 
 
 Greater Portion 
 of the Sympa- 
 thetic Nerve ; 
 the right lateral 
 walls of the 
 chest and abdo- 
 men, and the 
 stomach, in- 
 testines, liver, 
 spleen,and pan- 
 creas being re- 
 moved to bring 
 it in view : 
 
 ^» 3i 3) the superior, 
 middle, and in- 
 ferior cervical gan- 
 glia ; 4, the two 
 lines from this 
 figure include the 
 twelve dorsal gan- 
 glia ; 5, include 
 the four lumbar 
 ganglia ; 8, cardiac 
 plexus ; 9, solar 
 plexus ; 10, aortic 
 plexus ; a, the 
 larynx ; ^, the tra- 
 chea ; c, arch of 
 the aorta ; c/, ex- 
 ternal carotid ; c'', 
 internal carotid ; 
 rf, the heart ; e, e, 
 the diaphragm ; f, 
 the cardiac end of 
 the oesophagus ; g^ 
 thoracic ; and g', 
 abdominal aorta ; 
 k, the kidney ; 
 I, the supra-renal 
 capsule ; /, the 
 section of base of 
 the skull. 
 
232 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 ideas. The organ of voice is the larynx (behind the Fomum 
 Adami), the structure of which is complicated, and cannot 
 be here described (fig. 163, a). It consists of various 
 cartilages and muscles, the object of which is to tighten or 
 relax the margins of two folds of membrane, called the vocal 
 cords. By the vibrations of these cords voice is produced, 
 
 Fig. 164. 
 
 A, larynx and trachea on deep inspiration ; B, on phonation ; C, during falsetto 
 note when only a portion of the length of the cord vibrates ; D, approximation 
 of the ventricular bands or false cords as it occurs in straining the voice. 
 
 and by tightening or relaxing, separating or approximating 
 them, we obtain various modifications of voice. When a 
 high note is sounded, the cords are tense and close together 
 (fig. 164, B) ; and, on the contrary, when we sing a deep 
 bass note, they are relaxed and wide apart. The quality 
 and compass of the voice differ in individuals. In men, 
 the highest is the tenor ; the lowest, the bass ; the inter- 
 mediate, the barytone. In women, the corresponding 
 notes are the soprano, the contralto, and the mezzo-soprano. 
 The difference between the deep bass of a man and the 
 shrill soprano of a woman is that in the man the cords 
 are longer and less tense than in the woman. At the time 
 of puberty, more especially in the male, the larynx enlarges 
 
VOICE AND SPEECH. 233 
 
 from before backwards, thus increasing the length of the 
 vocal cords. During the period of enlargement the voice 
 ' breaks,' and the pitch, at the close of the process, will be 
 found to be about an octave lower than at first. Con- 
 sequently a boy who sang soprano now has a tenor voice, 
 and one who sang contralto becomes a singer in the bass 
 clef. A much slighter change occurs in the girl. 
 
 252. Speech is voice so modified by the action of the 
 throat, tongue, cheeks, and lips, as to mean or indicate 
 objects, properties, ideas, &c. This is language. If we 
 breathe quietly, without causing the vocal cords to vibrate, 
 and modify by the action of the mouth, &c., the volume of 
 the air expelled, we produce whispering. 
 
 Questions. 
 
 251, 252. Distinguish between voice, singing, whispering, and speaking. 
 Where is the organ of voice situated ? What is the appearance 
 of the glottis in inspiration, in expiration, and in singing a 
 note? What are the various registers of the human voice? 
 When the voice ' breaks,' why does it, in the male sex, fall 
 about an octave in pitch ? 
 
INDEX. 
 
 (L.= Latin; Gr. = Greek.) 
 
 PAGE 
 
 Abdomen (L. abdere^ to hide) 36 
 
 Abdominal respiration 165 
 
 Abducens (L. leading away) nerve. . .226 
 Abductor (L. leading away) muscles . . 30 
 
 Aberrations, in eye 201 
 
 Absorption 143 
 
 Accommodation, mechanism of 199 
 
 Acetabulum (L. aceiabie^ a small cup). 25 
 
 Acid, carbonic 55 
 
 Acids, inorganic, 54 ; organic 57 
 
 Acromion (Or. acro^ a point ; ontos^ 
 
 shoulder). 20 
 
 Actinozoa (Or. akiin^ a ray ; zoon^ 
 
 an animal), nervous system of. . . . .217 
 
 Actions, reflex 75 
 
 Adam's apple 49 
 
 Adductor (L. leading to) muscles 30 
 
 Adenoid (Gr, aden^ gland ; eidos, 
 
 like) tissue 147, 150 
 
 Adipose (L. adeps, fat) tissue 88 
 
 After-images 203 
 
 Air, composition of, 122 ; in lungs, 
 
 166 ; import.ince of. 121 
 
 Albumin (L. aibus, white) 56 
 
 Albuminoids (L. aihts^ white ; eidos, 
 
 like) 56 
 
 Albuminous matters 122 
 
 Alcohols (Arabic ai, the ; kokol, a 
 
 stain, or finely powdered) 58 
 
 Aliment 120 
 
 Alimentary system iiS 
 
 Amoeba (Gr. amoibe^ a change) iig 
 
 Amoeboid (Gr. ameibo, I change) 
 
 movement 82 
 
 Anabolic (Gr. anaballein, to build 
 
 up) process 71 
 
 Anatomy (Gr. ana ; iemnetn, to cut).. 8 
 
 Ankle 25 
 
 Annelidae (L. anellus, diminutive of 
 
 anmdtis, aring), nervous system in.217 
 Antf nervous system in 216 
 
 PAGE 
 
 Apncea (Gr. a, privative, or without ; 
 
 pneeiHy to breathe) 167 
 
 Appendix vermiformis (worm-like) .■ . .45 
 
 Aqueous humour 197 
 
 Arm, bones of. 20 
 
 Arteries, structure of. 1 13 
 
 Asphyxia (Gr. a, privative, or with- 
 out ; sphuxisy pulse) 167 
 
 Astigmatism (Gr. «, privative, or 
 
 without ; stigma, a point) 201 
 
 Atlas (,Gr. atlao, I sustain), the 15 
 
 Auditory canal 204 
 
 Auricle (L. dim. of auris, the ear). . . 204 
 
 Axis, the 15 
 
 Axis-cylinder . , 212 
 
 Bacteria (Gr. bacterion, a little 
 
 stick) in intestinal canal 141 
 
 Ball and socket joints 27 
 
 Bartholin, duct of (named after old 
 
 anatomist) 42 
 
 Bases, inorganic, in body 55 
 
 Bile, action of, 138 ; composition of, 
 139; fate of constituents of, 158; 
 
 formation of 155 
 
 Bile acids, 154 ; ducts 158 
 
 Bilirubin (L. bilis, bili ; ruber , red) , . 158 
 Biliverdin (L. bilisy bili ; viridis^ 
 
 green) 158 
 
 Birds, brain of 219 
 
 Bladder 50, 176 
 
 Blind spot 200 
 
 Blood, circulation of, 105 ; coagula- 
 tion of, 103 ; corpuscles of, 104 ; 
 composition of, 148 ; formation of, 
 73; general characters of, 101; 
 microscopical examination of, ici ; 
 plasma of, 103 ; sources of, T46 ; 
 
 use of 70, 71 
 
 Blood-glands, 147 ; pressure 114 
 
 Blood-vessels 105 
 
235 
 
 PAGE 
 
 Body in action 65 
 
 Bone, chemical nature of, 100 ; 
 
 growth of, 98 ; structure of. 97 
 
 Bone marrow 150 
 
 Bones, 13 ; of the ear 205 
 
 Bowels, digestion in 135 
 
 Bowman, capsule of 174 
 
 Brain, anatomy of, 38, 221 ; func- 
 tions of, 223; parts of 76, 218 
 
 Breathing, abnormal 167 
 
 Bronchi, 162 ; bronchial tubes 161 
 
 Brownian movement (named after 
 
 Brown, the celebrated botanist) 79 
 
 Brunner's glands (named after their 
 discoverer) 137 
 
 Cadaveric rigidity 78 
 
 Caecum (L. cescns^ blind) 45 
 
 CanalicuU (L. small canals) in bone... 97 
 
 Capillaries (L. capillus^ a hair) 114 
 
 Carbo-hydrates 57, 122 
 
 Carpus, the wrist 22 
 
 Cartilage 95 
 
 Casein (L. caseum, cheese) 56 
 
 Cat, brain of 2ig 
 
 Cells, chemical composition of, 82 ; 
 conditions of life of, 83 ; forms of, 
 81 ; parts of, 80 ; reproduction of, 
 84 ; sizes of, 81 ; varieties of, 84 ; 
 
 vitality of. 82 
 
 Cellular elements 80 
 
 Cement of tooth 126 
 
 Cerebellum (L. dim. of cerebrum).. . .222 
 
 Cerebrum (L. the brain) 223 
 
 Cervical (L. cervix.^ the neck) 15 
 
 Chemical changes in body 59 
 
 Chemical compounds, 54 ; elements, , .53 
 
 Chemistry of body 52 
 
 Cholesterin (Gr. chdie, bile ; stereos, 
 
 solid) 139 
 
 Chondrin (Gr. chondros) g6 
 
 Chorda tympani (L. chorda, cord ; 
 
 iympanutn^ drum 189 
 
 Choroid coat (Gr. chorion^ the 
 chorion — a foetal membrane — 
 
 eidoSf like) igs 
 
 Chyle (Gr. chulos, juice) 143, 149 
 
 Chyme (Gr. chwnos, juice) 131 
 
 Cilia (L. cilium, an eyelash) 85 
 
 Ciliary movement, 86 ; muscle, 200 ; 
 , processes 195 
 
 PAGE 
 
 Circulation, organs of.. .51, 105, 109, iii 
 
 Circumvallate papillae igo 
 
 Clavicle (dim. of clavis, a key) 20 
 
 Clot in brain 228 
 
 Cochlea 208 
 
 Cold-blooded 179 
 
 Cold spots 188 
 
 Colon (Gr. koilo7i, hollowed) 44 
 
 Condyle (Gr. kondulos, a knuckle)... .24 
 
 Connective tissue 32, 90 
 
 Contractility 69 
 
 Convolutions 222 
 
 Corpora quadrigemina (L. quadri- 
 
 gemimis,. fourfold) 224 
 
 Corpora striata (L. corpus, a body ; 
 
 striata, grooved) 222 
 
 Corpus callosum (L. callosus, hard).. 223 
 
 Corpuscles, blood 102 
 
 Corti, organ of (named after dis- 
 coverer, the Marchese di Corti). ... 209 
 
 Costal (pertaining to ribs) 18 
 
 Crab, nervous system of 216 
 
 Cramer, images of igg 
 
 Cranial nerves 225 
 
 Cranium (Gr. kranos, a helmet) iS 
 
 Crustacea, nervous system of 217 
 
 Crystalline lens 197 
 
 Cuboid (Gr. kubos, cube; eidos, like). 25 
 Cuneiform {cimeits, a wedge ; for- 
 
 ma^ shape) 25 
 
 Cutis vera (L. true skin) 177 
 
 Death 77 
 
 Decomposition 60 
 
 Deglutition (L. deglutitio, swallow- 
 ing) 129 
 
 Dentine (L. dens, a tooth) 126 
 
 Dermis 177 
 
 Diaphragm (L. diapkragjsta, a par- 
 tition wall) 35 
 
 Diastole (Gr. diastole, drawing 
 
 apart) loS 
 
 Diet 124 
 
 Digestion, organs of, 39 ; time in, 
 
 133 ; favourable conditions of. 134 
 
 Drum of ear 204 
 
 Duodenum (L. duodeni, twelve, or 
 
 twelve fingers' breadth) 44 
 
 Dying 78 
 
 Dyspnoea (Gr. dits, difficult; pneei?i, 
 I to breathe) 167 
 
236 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 PAGE 
 
 Ear, anatomy of, 204 ; functions of, 
 
 208 ; structure of internal 206 
 
 Echinodermata (Gr. echuios, the 
 sea hedgehog ; derma^ skin), ner- 
 vous system in 217 
 
 Effluvia 192 
 
 Elastic tissue 90 
 
 Elements, chemical 53 
 
 Enamel ....i 126 
 
 End-bulbs 186 
 
 Endolymph (Gr. ettdos, within) 207 
 
 Endothelium (Gr. endos, within ; 
 
 ikeliay a papilla) 85 
 
 Energy 68, 82 
 
 Enzymes (Gr. ^«, in ; zumne^ 
 
 leaven) 62, 82 
 
 Epidermis (Gr. epi, upon ; derma, 
 
 skin) 177 
 
 Epiglottis (Gr. epi, upon ; giossa, 
 
 tongue) i6z 
 
 Epiphyses (Gr. epij upon ; phyo^ I 
 
 grow) 99 
 
 Epithelium (Gr. epi, upon ; tkelia, 
 
 a papilla) 85 
 
 Equilibrium 182, 210 
 
 Erect position 25 
 
 Eustachian tube (named after 
 Eustachius, an ancient anatomist).. 204 
 
 Expiration 163 
 
 Eye, 194 ; appendages of, 197 ; coats 
 of, 195 ; humours of, 197 ; muscles 
 
 of, 197 ; refractive media of 195 
 
 Eyelids 197 
 
 Face, bones of 18 
 
 Facial nerve 226 
 
 Faeces 142 
 
 Fascia (L. bandage) 28 
 
 Fasciculi (L. small bundles) of 
 
 muscle 92 
 
 Fat, 88 ; combustion of, 58 ; com- 
 position of, 58 ; digestion of, 140 ; 
 
 formation of 156 
 
 Fatigue 94 
 
 Femur 23 
 
 Fenestrae(L.^«^j^rrt!, a window). 206, 208 
 
 Ferments 61 
 
 Fibrillae (L. small fibres) of muscle.. . .92 
 
 Fibrin 103 
 
 Fibrinogen (L.Jidrin, and gennao, 
 I produce) 103 
 
 PAGE 
 
 Fibrous elements 89 
 
 Fibrous tissue 89 
 
 Fibula 24 
 
 Filiform (L. filum, a thread ; /or- 
 
 nta, likeness) papiUee 189 
 
 Fish, brain of 218 
 
 Flavours 123, 190 
 
 Food, 120 ; analysis of, 124 ; classi- 
 fication of, 122 ; digestion of, 131 ; 
 necessity for, ^\ ; quantity of, 
 
 123 ; relation of to work 123 
 
 Foot, bones of 35 
 
 Frog, brain of 218 
 
 Fungiform (L. /ungtis, a mushroom ; 
 forma, likeness) papillae 189 
 
 Gall-bladder 46, 152 
 
 Ganglia (Gr. ganglion, a tumour). ... 21 7 
 
 Gastric glands, 130 ; juice 132 
 
 Gelatinous matters (L. gelare, to 
 
 congeal) 122 
 
 Glands, salivary, 41, 42 ; types of.... 172 
 Globulins (L. globulus, a ball). .•56, 103 
 Glosso - pharyngeal nerve (Gr. 
 
 glossa, tongue) 226 
 
 Glottis 161 
 
 Glycogen (Gr. glitcos, sweet ; 
 
 gennao, I produce) 156 
 
 Growth 171 
 
 Gurnard, brain of 218 
 
 Haemoglobin (Gr. kainia^ blood ; 
 
 globulus, a little ball) 158, 170 
 
 Hair 178 
 
 Hair-cells 207 
 
 Haversian canals of bone (named 
 
 after Clopton Havers, a Dutch 
 
 anatomist) 98 
 
 Hearing 210 
 
 Heart, cavities of, 107 ; position of, 
 
 106; structure of, 106; rhythmic 
 
 movements of, 116; valves of. 108 
 
 Heat, animal, 65, 179 ; liberation of. . . 70 
 Hepatic cells (Gr. hepatikos^ of the 
 
 liver) 152 
 
 Hinge jcunts 28 
 
 Hip-joint 27 
 
 Hippuric acid (Gr. hippos, a horse ; 
 
 ouron, urine) 176 
 
 Histology (Gr. histos, a tissue ; 
 
 logos, a description) 79 
 
INDEX. 
 
 237 
 
 PAGE 
 
 Hot Spots 188 
 
 Hydrozoa (Gr. hudor, water ; zooii^ 
 
 animal) 217 
 
 Hypermetropia 201 
 
 Hypoglossal nerve (Gr. hypo^ 
 
 under ; glossa, tongue) 226 
 
 Humerus 20 
 
 Humours of eye 197 
 
 Ileo'caecal valve 45 
 
 Ileum (Gr. eiiein, to turn or twist). . ..44 
 
 Illusions, optical 203 
 
 Impulse, nervous 69 
 
 Incus (L. tftcTts, an anvil) 205 
 
 Infundibula (L. i?ifu7idere^ to pour 
 
 into) 162 
 
 Inosite (Gr. w, inos^ muscle) 57 
 
 Insalivation 127 
 
 Insecta, nervous system in 127 
 
 Inspiration 163 
 
 Intervertebral discs 14 
 
 Intestinal juice 140 
 
 Intestine, large, 44 ; small 40, 44 
 
 Intestine, changes in great, 141 ; 
 structure of great, 137 ; digestion 
 in small, 131 ; muscular coat of 
 
 small, 137; structure of small 136 
 
 Iris (Gr. iris, coloured halo or 
 circle) 195 
 
 Jejunum (L. jejunus, hungry, from 
 this portion of bowel being usually 
 found empty) 44 
 
 Joints 26, 27 
 
 Katabolic process (Gr. kata, down ; 
 
 hallein, to throw) 71 
 
 Kidneys, anatomy of, 50 ; action of, 
 
 175 ; structure of 173 
 
 Kreatinin (Gr. kreas, flesh) 176 
 
 Labyrinth (Gr. laburifttkos, a maze). 207 
 Lachrymal (L. lachrymal tears) 
 
 apparatus 198 
 
 Lacteals (L. /izc, milk) 143 
 
 Lactose (L lac, milk) 57 
 
 Lacunae (L. laais, a lake) 98 
 
 Language 233 
 
 Larynx 49, 161, 232 
 
 Latent stimulation period 94 
 
 Leg, bones of 24 
 
 PAGE 
 
 Lens in eye 187 
 
 Leucocytes (Gr. leucos, white; 
 
 kutos, a cell or bladder) 83 
 
 Levers 180 
 
 Lieberkuhn, glands of (named after 
 
 old anatomist) 137 
 
 Life, definitions of 76 
 
 Ligaments 14, 32 
 
 Ligamentum nuchae (of the neck) 90 
 
 Liver, anatomy of, 46; circulation 
 in, 152 ; description of, 151 ; func- 
 tions of, 155 ; lobules of 154 
 
 Living beings 7 
 
 Lower extremity, bones of 12 
 
 Lumbar (belonging to the loins) 14. 
 
 Lungs, anatomy of, 47, 161 ; capa- 
 city of, 166 ; structure of 16& 
 
 Lymph 71, 14a 
 
 Lymphatics 145 
 
 Malar (L. mala, belonging to the 
 
 cheek) bone 18 
 
 Malleus (L. a mallet) 205 
 
 Malpighian bodies in kidney (named 
 after the discoverer, Malpighi, an 
 
 Italian anatomist) 174^ 
 
 Malpighian bodies in spleen 149 
 
 Man, nervous system in 220 
 
 Marrow of bone 83 
 
 Mastication 125 
 
 Matrix (L. mater, mother) of cartil- 
 age 96 
 
 Mechanics, animal 180 
 
 Mediastinal spaces (L. in fnedio 
 
 stare, to stand in the middle) 49 
 
 Medulla oblongata (L. medulla, mar- 
 row ; oblongata, elongated). . . 222, 224 
 
 Medullary canal of bone 99 
 
 Membranes, serous, 37 ; mucous 34 
 
 Mesenteric glands 145 
 
 Mesentery (Gr. mesos, middle ; 
 
 ejiieron, intestine) 44, 143, 
 
 Mitral valve (like a bishop's mitre) . , 108 
 
 Molecular movements 79 
 
 Molecule (dim. of moles, a mass) 79 
 
 Mollusca (L. mollziscitm, a shell- 
 fish), nervous system in 217 
 
 Motor areas 224 
 
 Motor-oculi nerve 225 
 
 Mouth 7 40 
 
 Movements, respiratory 165 
 
238 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 PAGE 
 
 Mucinogen (L. mucus, mucus ; Or. 
 
 gennao^ I generate) 172 
 
 Mucous membranes 34 
 
 Muscae volitantes (L. muscle, flies; 
 
 volitanteSy flitting) 202 
 
 Muscle, chemical nature of, 93 ; 
 
 general phenomena in, 69 ; heat 
 
 phenomena of, 95 ; effects of 
 
 stimulatiifg, 93 ; structure of, 91 ; 
 
 work done by a 94 
 
 Muscles, the 28 
 
 Muscular sense, 211 ; tissue 91 
 
 Myopia (Gr. vtuo, to close ; ops, the 
 
 eye) 201 
 
 Myosin (Gr. muon, muscle) 56, 93 
 
 Nares 47 
 
 Nasal bones ^ 18 
 
 Nerve-cells 213 
 
 Nerves, classification of, 74, 225 ; 
 
 functions of, 214, 224 ; structure of.212 
 Nervous system, 211 ; anatomy of, 
 38 ; development of, 215 ; influ- 
 ence of. 73 
 
 Neurolemma (Gr. neuron, a nerve ; 
 
 letnnta, a coat) 213 
 
 Non-striated muscle 91 
 
 Nucleo-albumin 139 
 
 Nucleolus (L. dim. of nucleus). ... 80, 82 
 
 Nucleus (L. a kernel) 80, 8z 
 
 Nutrition 170 
 
 Objects, sizes of 203 
 
 Occipital (L. occiput, back of head) 
 
 bone 17 
 
 Odontoid (L. odonto, tooth ; Gr. 
 
 eidos, form) process 15 
 
 Olfactory nerve 225 
 
 Ophthalmoscope (Gr. opkthalmos, 
 
 the eye ; skopeo, I see) ig6 
 
 Optic nerve, 225 ; papilla 200 
 
 Optic thalami (Gr. thalamos, a 
 
 bed) 222, 223 
 
 Organ of Corti 207 
 
 Organic compounds 56 
 
 Organic matter, instability of 63 
 
 Organisms in intestine 141 
 
 Organs, the internal 35 
 
 Os (L, OS, a bone) calcis, heel bone, 
 
 25 ; 05 coxas, hip bone, 23 ; os 
 
 magnum, in wrist 22 
 
 PAGE 
 
 Oxaluric acid (Gr. oralis, wood- 
 sorrel ; ourou, urine) 176 
 
 Oxidations 60 
 
 Pacinian bodies 187 
 
 Palate bone 18 
 
 Pancreas, 40, 46 ; structure of 139 
 
 Pancreatic juice 140 
 
 Papillx of tongue i8g 
 
 Parietal (L. paries, a wall) bone 17 
 
 Parotid gland 41 
 
 Patella 24 
 
 Pathetic nerve 226 
 
 Pelvis (L. a basin). 23 
 
 Pepsin (Gr. Pepsis, digestion). 132 
 
 Peptones (Gr. pepio, I digest) 132 
 
 Pericardium (Gr. peri, around ; 
 
 kardia, the heart) 107 
 
 Perilymph 207 
 
 Peristalsis (Gr. peri, around ; stello, 
 
 I contract) 138 
 
 Peyer's glands (after discoverer). 147, 150 
 
 Phalanges 21 
 
 Pharynx 45 
 
 Phosgenes (Gr. phos, light ; gennao, 
 
 I produce) 202 
 
 Physiology (Gr. phusis, nature ; 
 
 logos, a description) 8 
 
 Pigeon, brain of 219 
 
 Pigment, description of 87 
 
 Pineal (Gr. pinea, a pine cone) gland. 151 
 Pisiform bone (Gr. pisutn, a pea ; 
 
 forma, shape) 22 
 
 Pituitary (Gr. pituita, mucus) body.. 151 
 
 Plasma 148 
 
 Pleura (Gr. pleura, the side — the 
 
 plural q{ pleuron, a rib) 48 
 
 Pneumogastric nerve (Gr. pneuino, 
 
 lung ; gaster, the stomach) 226 
 
 Pomum Adami (Adam's apple) 232 
 
 Pons Varolii (L. pons, bridge ; Varo- 
 
 lius, the discoverer) 224 
 
 Portal vein 152 
 
 Portio dura (L. Portion part ; durus, 
 
 hard) nerve 226 
 
 Portio mollis (L. portio, part ; mol- 
 lis, soft) nerve 226 
 
 Position, the erect 25 
 
 Presbyopia (Gr. presbys, old ; oPs, 
 the eye), due to defect in mechan- 
 ism of accommodation 200 
 
INDEX. 
 
 239 
 
 PAGE 
 
 Pronation (L. promts^ inclined for- 
 wards) ; 21, 30, 32 
 
 Proteid 59 
 
 Proteoses 132 
 
 Protoplasm (Gr. protos, first ; plasso^ 
 
 I form) 80, 81 
 
 Protozoa (Gr. protos, first ; zoon^ 
 
 animal) : 216 
 
 Ptyalin (Gr. ptitalon^ saliva) 127 
 
 Pulse (L. pulsus, a stroke) 115, 117 
 
 Pus 88 
 
 Rabbit, brain of 219 
 
 Racemose (L. racetnuSt a cluster of 
 
 grapes) gland 42 
 
 Radius (L. spoke of wheel) 21 
 
 Ranvier, nodes of, in nerve. 213 
 
 Receptaculum chyli (receptacle for 
 
 chyle) 14s 
 
 Rectum (L. rectus, straight) 45 
 
 Reductions 61 
 
 Reflex acts 75 
 
 Reptile, brain of 219 
 
 Respiration, and circulation, 116 ; 
 
 conditions of, 161 ; description of, 
 
 i59» 163 ; mechanism of, 164 ; 
 
 types of, 165 ; process 169 
 
 Respiratory organs, anatomy of 47 
 
 Retiform (L. rete^ a net) tissue 147 
 
 Retina (L. rete, a. net), structure of, 
 
 196; formation of image on '. .203 
 
 Ribs 19 
 
 Rivinus, duct of 42 
 
 Rotation, sense of 210 
 
 Round ligament of hip 27 
 
 Sacrum (L. sacer, sacred) 17 
 
 Saline matters 123 
 
 Saliva, 127 ; salivary glands 41 
 
 Salts 56 
 
 Sanguification 145 
 
 Sapidity 123 
 
 Sarcolemma (Gr. sarkos, flesh ; 
 
 lemma, a web) 92 
 
 Sarcous elements (Gr. sarkos, flesh). ,92 
 Scalse of cochlea (L. scala, a stair) . .208 
 Scaphoid (Gr. skaphe, a boat) bone ... 22 
 
 Schwann, white substance of 212 
 
 Sebaceous (L. sebuvi, suet or fat) 
 
 glands 178 
 
 Secretion 171 
 
 PAGE 
 
 Semicircular canals 206 
 
 Semilunar (L. se^ni, half; Inna, 
 
 moon) bone, 22 ; valves 108 
 
 Senses 184 
 
 Sensori-motor nerves 225 
 
 Serous membranes 37 
 
 Serpula, nervous system in 216 
 
 Serum 86 
 
 Sight 193 
 
 Skeleton (Gr. skeleios, dried up) n 
 
 Skin 33, 177, 178 
 
 Skull (L. satiella, a cup) 17 
 
 Smell 192 
 
 SSmmering, yellow spot of (after 
 
 discoverer) ig6 
 
 Speech 233 
 
 Sphenoid (Gr. sphen, wedge ; eidos, 
 
 likeness) bone 17 
 
 Spinal cord 35, 75, 227 
 
 Spinal accessory nerve 226 
 
 Spinal nerves 228 
 
 Spleen 47, 147, 149 
 
 St Martin, case of 133 
 
 Standing 182 
 
 Stapes (L. a stirrup) 205 
 
 Starch, animal 156 
 
 Starchy matters • 122 
 
 Stearin (Gr. stear, fat) 58 
 
 Steno's duct 42 
 
 Sternum 19 
 
 Stomach 39, 44, 130, 131, 133 
 
 Striated muscle 81 
 
 Sub-lingual gland 127 
 
 Sub-maxillary gland 127 
 
 Sudoriparous glands (L. sudor, 
 
 sweat ; pario, I produce) 177 
 
 Supination (L. supinus, lying on 
 
 back) 21, 30, 32 
 
 Supra-renal bodies 50, 147, 150 
 
 Suspensory ligament 200 
 
 Suture (L. siiere, to stitch) 17 
 
 Swallowing 129 
 
 Sweat, 178 ; sweat-glands 177 
 
 Sympathetic nerve 229, 230, 231 
 
 Symphysis (Gr. sumpkuo, I grow 
 
 together) 23 
 
 Synovia (Gr. sun, with ; oon, an egg).. 26 
 Synthesis (Gr. sujithesis, putting 
 
 together) 61 
 
 Syntonin 132 
 
 Systole (Gr. siistole, a contraction). ..108 
 
240 
 
 ELEMENTARY HUMAN PHYSIOLOGY. 
 
 PAGE 
 
 Tarsus 25 
 
 Taste, i8g ; taste-bulbs 189 
 
 Taurin (L. tattrusy a bull) 139, 158 
 
 Teeth 126 
 
 Temperature, sensations of 188 
 
 Temporal bone 17 
 
 Tendon 90 
 
 Terminal organs 185 
 
 Tetanus (Gr. teino, I stretch) 94 
 
 Thigh, bones of 23 
 
 Thoracic duct 145 
 
 Thorax (Gr. thorax, cl cuirass, or 
 
 coat of mail) 47, 164 
 
 Throat 41 
 
 Thymus body 147, 150 
 
 Thyroid gland 48, 147, 150 
 
 Tibia 24 
 
 Tissues, the soft, 23 ; structure of, 
 
 79 ; respiration of 169 
 
 Tongue, 126 ; papillas of 189 
 
 Tooth, structure of 126 
 
 Tortoise, brain of 218 
 
 Touch, 186 ; touch-bodies 186 
 
 Trachea 48, 161 
 
 Trapezium (from geometrical form) 
 
 bone 22 
 
 Trapezoid (from geometrical form) 
 
 bone 22 
 
 Tricuspid valve 108 
 
 Trigeminal (L. three parts) nerve. . . .226 
 Trochanters (Gr. irochao., I run or 
 
 roll) 24 
 
 Trochlear (Gr. trochleay a pulley) 
 
 nerve 226 
 
 Tubular elements 95 
 
 Tubuli uriniferi (uriniferous tubules). 173 
 Turbinated bones (L. turbo, a top),. 191 
 
 Tympanum (L. a drum) 204 
 
 Tyrosin (Gr. tyros, cheese) 140 
 
 Ulna (L. a cubit) 21 
 
 Unciform bone (L. nnctis, a hook ; 
 
 forma, form) 22 
 
 Upper extremity, bones of 20 
 
 Urea (Gr. otiron, urine) 59, 157, 176 
 
 PAGE 
 
 Ureter 176 
 
 Uric acid 50, 176 
 
 Urine 175, 176 
 
 Vagus (L. vagare., to wander) nerve..226 
 
 Valves in veins 115 
 
 Veins, circulation in the 115 
 
 Ventilation 169 
 
 Ventricle (L. ventriculus, venter^ 
 
 the belly) of the heart 107 
 
 Vertebra (L. verto, I turn)> charac- 
 ters of a 14 
 
 Vertebral column 14 
 
 Vertebrata, nervous system of, 217 ; 
 
 structure of 119 
 
 Villi (L. vilbis, a shaggy hair), 
 
 functions of, X37 ; structure of. 11& 
 
 Vision, 193 ; defects of organs of, 
 20T ; mechanism of, 198 ; with 
 two eyes, 204 ; subjective pheno- 
 mena of 202 
 
 Visual angle 203 
 
 Vitreous (L. vitrtmi, glass) humour.. 197 
 
 Vocal cords 161, 232 
 
 Vomer (L. a ploughshare) i3 
 
 Warm-blooded 179 
 
 Waste matters 57. 58, 66, 71 
 
 Water 54, 122 
 
 Weber on touch 187 
 
 Wharton's duct 42- 
 
 Whispering 233 
 
 White fibrous tissue 89 
 
 Windpipe 48 
 
 Work, relation of food to 123 
 
 Wrist, bones of 21, 22 
 
 Xanthin (Gr. xantkos, yellow) 176 
 
 Yeast-cells 6i 
 
 Yellow elastic tissue 90 
 
 Yellow spot 196 
 
 Zymolysis (Gr. zuntnS, leaven ; lusis, 
 dissolving) 61 
 
 Edinburgh : 
 Printed by W. & R. Chambers, Limited. 
 
APPENDIX. 
 
 SYLLABUS OF THE SCIENCE DEPARTMENT, 
 SOUTH KENSINGTON. 
 
 SUBJECT XIV.— HUMAN PHYSIOLOGY. 
 
 GENERAL INSTRUCTIONS. 
 If the rules are not attended to, tha paper will be cancell ed. 
 
 You may take the Elementary, or the Advanced, or the Honours 
 paper ; but you must confine yourself to one of them. 
 
 Put the number of the question before your answer. 
 
 The value attached to each question in the Elementary and 
 Advanced papers is shovirn in brackets after the question ; but a full 
 and correct answer to an easy question will in all cases secure a larger 
 number of marks than an incomplete or inexact answer to a more 
 difficult one. 
 
 Your name is not given to the examiners, and you are forbidden to 
 write to them about your answers. 
 
 You are to confine your answers strictly to the questions proposed. 
 The examination in this subject lasts for three hours. 
 
APPENDIX. 
 
 Ill 
 
 FIRST STAGE OR ELEMENTARY EXAMINATION, 1890. 
 
 Instructions. — You are permitted to attempt only eight questions. 
 
 The value attached to each question is indicated by the numbers in brackets. 
 
 1. What structures form the walls of the thorax or chest ? How is 
 
 the thorax made air-tight? What important viscera are con- 
 tained in it, and what positions do they occupy In It ? Explain 
 how changes in the diaphragm alter the size of the thorax. 
 
 [IS.] 
 
 2. If a heart, a. sheep's heart, for instance, removed from the body, 
 
 were put before you, how could you tell which was the top, 
 which the bottom, which the front, and which the back? 
 What are the chief differences between the left ventricle and 
 the right ventricle ; and what purposes are served by these 
 differences? [15.] 
 
 3. What is the spinal cord? Where is it placed? Explain how the 
 
 spinal cord is protected from injury by the structure and 
 arrangements of the walls of the cavity in which it lies. 
 
 [IS-] 
 
 4. Of what chemical elements are fat and starch composed? How 
 
 do fat and starch differ from each other ? What changes does 
 starch and what changes does fat undergo in the alimentary 
 canal ? Where and how are those changes brought about ? 
 
 [IS-] 
 
IV ELEMENTARY HUMAN PHYSIOLOGY. 
 
 S. What is the most important substance and, next to the water, the 
 most abundant substance present in urine ? Of what chemical 
 elements is this substance composed, and how does it come 
 about that the kidneys are always to a greater or less extent 
 engaged in secreting this substance? [lo,] 
 
 6. What do the red and white corpuscles of the blood look like when 
 
 a drop of blood is examined under a high power of the micro- 
 scope, and how do they differ from each other? State an 
 important use of the red corpuscles. [lO.] 
 
 7. How in a dead body can you tell an artery from a vein ? What 
 
 are the chief differences between them, and why are they thus 
 different? [10.] 
 
 Z. What are the two chief parts of the skin, and how do they differ 
 from each other ? How does the skin of the lip differ from the 
 skin of the heel, and why ? , . [10.] 
 
 9. What differences can be observed, without the aid of any micro- 
 scope, between (a) a bone just firesh from the body, (b) one which 
 had been dried and kept for some time, and {c) one which had 
 been steeped in acid for some time? [10.] 
 
 10. What is meant, in speaking of vision, by ' the blind spot,' and 
 
 how' can its presence be demonstrated? What conclusions 
 concerning the nature of sight can be drawn from the existence 
 of the blind spot? [10.] 
 
 11. What parts go to form the hip-joint? What movements of the 
 
 hip-joint can be carried out? How are they limited, and 
 why? [10.] 
 
APPENDIX. 
 
 12. Describe the course taken by the air in breathing until it reaches 
 the glottis or pharynx, and explain why it is better to breathe 
 through the nose than througji the mouth. [lo.] 
 
 FIRST STAGE OR ELEMENTARY EXAMINATION, 189I. 
 
 Instructions. — You are permitted to attempt only eight questions. 
 
 The value attached to each question is indicated by the numbers in brackets. 
 
 I. Describe the form, position, and general appearance of the sternum. 
 What is the nature of the material of which it is composed ? 
 What changes of position does it undergo in breathing ? 
 
 [IS.] 
 
 Give an account of what may be seen by examining the right 
 auricle of the heart from the outside. State how you would 
 proceed to lay open the cavity of the right auricle in orderlo 
 show to the best advantage the stracture and relations of the 
 auricle, and carefully describe what may be seen in the auricle 
 tlius laid open. [15.] 
 
 3. Describe the form, position, and general structure of the small 
 intestine. How does the small intestine differ from the large 
 intestine ? State briefly the changes which the food undergoes 
 (l) in the small, (2) in the large intestine. [15.] 
 
VI ELEMENTARY HUMAN PHYSIOLOGY. 
 
 4. Give an account of a valve in a vein, describing how it appears 
 
 when seen by the naked eye or with the help of a lens. De- 
 scribe its nature, and explain how it works. Which veins 
 possess many valves, which few, and which none at all ? 
 
 [150 
 
 '" _ 
 
 5. What is the nature of cartilage ? How does it differ from bone, 
 
 and from tendon? State as fully as you can in what parts of a 
 full-grown body cartilage is found. [10.] 
 
 6. Describe the portal vein, stating how it begins, where it runs, and 
 
 how it ends. Does the blood as it passes along the portal vein, 
 after a full meal has been taken, differ from the blood passing 
 along the same vein when no food has been taken for some 
 time ; and if so, how? [10.] 
 
 7. What is the structure of the diaphragm ? How does the diaphragm 
 
 act in breathing ? [lo.] 
 
 8. What is a clot of blood composed of? When you cut a large clot 
 
 of blood open, does the inside look different from the outside ; 
 and if so, why? How may a colourless clot be obtained? 
 
 [10.] 
 
 9. When you touch a body with your finger you can tell whether the 
 
 body is rough or smooth ; why cannot you do this if the skin 
 of the finger be injured or removed ? In what part of the body 
 is the sense of touch most acute, and in what parts least ? How 
 can you determine this accurately ? [10.] 
 
 10. What is the general structure of the spinal cord? Explain what 
 happens if the spinal cord be damaged (i) at the level of the 
 bottom of the neck, (2) at the level of the middle of the back. 
 
 [10.] 
 
APPENDIX. Vli 
 
 11. Explain as fully as you can what you do when you 'hold your 
 
 breath.' What changes are taking place in your lungs while 
 you are holding your breath? Why cannot you hold it for 
 more than a very short time ? [lo.] 
 
 12. After violent exercise a man says 'he is very hot.' Is he really- 
 
 hotter than usual ? If not, explain how this is. [lO.] 
 
 FIRST STAGE OR ELEMENTARY EXAMINATION, 1893. 
 
 Instructions. — ^You are permitted to attempt only eight questions. 
 
 The value attached to each question is indicated by the numbers in brackets. 
 
 1. What is the abdomen ? What structures form its walls ? State 
 
 the more important organs which are placed in the abdomen, 
 giving the positions of each, and expUining in particular the 
 manner in which the alimentary canal passes through the 
 abdomen. [15.] 
 
 2. Describe the semilunar valves of the aorta, stating their exact 
 
 position, their appearance, form, and structure (as far as the 
 latter can be made out without a microscope), and explaining 
 how they act in the work of the circulation. [15.] 
 
 3. Explain how the chest is enlarged when we breathe in, and how 
 
 it becomes small again when we breathe out ; and show why air 
 goes into the chest in breathing in, and why it comes out in 
 
Till ELEMENTARY HUMAN PHYSIOLOGY. 
 
 breathing out. About how far into the chest does the air 
 which we take in at an ordinary breath go? [iSO 
 
 4. What is the general structure of the mucous membrane of the 
 stomach, and what are the characters of the juice which it 
 secretes ? Describe the changes which a piece of meat and a 
 piece of bread undergo in the stomach. [15.] 
 
 3. How would a cupful of blood drawn from some artery in a limb, 
 say the artery in the thigh, differ in appearance from a cupful of 
 blood drawn from the neighbouring vein ? To what important 
 changes undergone by the blood in passing from the artery to 
 the vein is this difference of appearance due ? Where and how 
 have these changes been brought about? [10.] 
 
 6. State the structure of a muscle and of its tendon as far as can be 
 
 made out without the use of a microscope. What happens to 
 the muscle and to the tendon when the muscle contracts ? 
 
 [10.] 
 
 7. What is bile ? Where is it formed ? Where does it flow to when 
 
 food has recently been taken, and where does it go when food 
 has not been taken ? What are its chief uses ? [10.] 
 
 3. In what parts of the body are capillary blood-vessels most abun- 
 dant and most close set ? In what parts of the body are they 
 scanty and far apart? From what parts of the body are 
 capillaries entirely absent ? [10.] 
 
 •9. What is the crystalline lens ? Where is it placed ? What is its 
 use ? When and why does it change in shape ? How is the 
 change brought about ? [10.] 
 
APPENDIX. _ . IX 
 
 10. Describe the general structure of a kidney, and state the general 
 
 nature of the work which the ktdnefys perform. If the kidneys 
 fail to excrete tirine, what changes take place in the blood ? 
 
 [10.] 
 
 11. What do you understand by absorption from the alimentary canal? 
 
 What are the things which are absorbed from the alimentary 
 canal ? What are the two paths along one or other of which 
 the absorbed matters travel, and whither does the one and the 
 other lead them? [lo.] 
 
 12. Explain how it is that when a man 'breaks his neck' he dies at 
 
 once, but if he ' breaks his back ' he may live for a long while 
 afterwards. [lb.] 
 
 13. If n person who is standing or sitting up feels faint, what is the 
 
 best thing to do to prevent his fainting ? Explain the reason of 
 the measures which you would adopt. [10.] 
 
 FIRST STAGE OR ELEMENTARY EXAMINATION, 1893. 
 
 Instructions. — You are permitted to attempt only eight questions. 
 
 The value attached to each question is indicated by the numbers in brackets. 
 
 What is the spinal column or backbone ? Of what structures is 
 it made up, and how are these structures connected together so 
 as to form the" backbone ? How does the spinal column end 
 above and below ? ['S-l 
 
X ELEMENTARY HUMAN PHYSIOLOGY. 
 
 2. How can you tell by examining the outside of a heart which is its 
 
 right side and which is its left side? What are the differences 
 between the inside of the right and left sides of the heart ? To 
 what differences in the use of each side of the heart do these 
 differences in structure correspond? [iS-] 
 
 3. Where is the large intestine placed in the body ? How does it 
 
 begin and how does it end; and how does it lie between its 
 beginning and end ? How does it differ in structure from the 
 small intestine ? What changes does food undergo inside the 
 large intestine ? [iSO 
 
 In what direction and in what manner does the blood flow in a 
 large artery, as of the leg, and in what direction and in what 
 manner does it flow in a large vein of the same leg? What 
 makes it flow in the direction and in the manner you describe 
 in the artery and in the vein ? How does the blood pass from 
 the artery into the vein ? What is the blood doing while it is 
 passing from the artery into the vein, and what is the use of this 
 to the leg? [15.] 
 
 5. What does a long bone taken fresh out of an animal look like 
 when it is cut in two lengthwise ? What would it look like if 
 it were cut in two after it had been boiled or had been buried 
 for a long time ? What is the cause of the differences ? What 
 happens to a bone when it is burnt in a fire? [10.] 
 
 By what organ is urine formed ? Where is this organ placed on 
 each side of the body, and what does it look like ? What are 
 the most important substances of which urine is composed ? 
 Where do these substances come from before they find their 
 way into the urine, and why must they always be got rid of to 
 a greater or less extent ? [10.] 
 
APPENDIX. XI 
 
 7. Your body is always warm while it is alive, and it is just as warm 
 on a cold day as on a hot day. Why is your body warm, and 
 how is it kept equally warm both in cold and hot weather? 
 
 [10.] 
 
 8. With what kinds of food-stuffs should the body be supplied each 
 day, and in about what proportions? How do the several 
 food-stuffs differ essentially from each other? On which one 
 food-stuff could an animal be kept alive ? Why is it better 
 and more economical not to eat this one food-stuff only, but to 
 mix the others with it ? [10.] 
 
 9. Where is the pancreas or sweet-bread placed in the body? What 
 is the pancreas ? What does the pancreas do which makes it 
 useful to the body ? * [10.] 
 
 10. What muscles are attached to the eyeballs ? What movements of 
 the eyeballs are brought about by the contractions of these 
 muscles ? What is the cause of squinting ? [10.] 
 
 II. What nerves are connected directly with the spinal cord, and how 
 are they connected ? If you saw one person who could move 
 his arm but could not feel vrith his fingers, and another person 
 who could feel but could not move his arm, what parts would 
 you suppose were injured or diseased in each of these persons ? 
 
 [ID.] 
 
 12. If you take a sharp walk or a quick run you breathe faster. What 
 is the cause of your breathing faster, and of what advantage to 
 the body is the quicker breathing ? What other thing? besides 
 rapid exercise make a person breathe very quickly, and how is 
 it that they thus affect the breathing? [10.] 
 
Xn ELEMENTARY HUMAN PHYSIOLOGY. 
 
 FIRST STAGE OR ELEMENTARY EXAMINATION, 1894. 
 
 Instructions. — You are permitted to attempt only eight questions. 
 
 The value attached to each question is indicated by the numbers in brackets. 
 
 1. Where and how is the diaphragm placed in the body? What 
 
 organs lie immediately above and what immediately below it ? 
 What structures pass through it? How does the diaphragm 
 work in breathing, and what makes it work? ['S-] 
 
 2. How would you place a heart in front of yourself so as to see the 
 
 left auricle most easily ? What does the left auricle look like 
 as seen from the outside, and what does its inside look like 
 when laid open? What blood-vessels enter the left auricle, and 
 how is it connected with the left ventricle? [15.] 
 
 3. What is the general shape and appearance of the stomach ? 
 
 What is its general structure ? In wTiat way does the internal 
 lining of the stomach differ from that of the small intestine ? 
 What changes does proteid food undergo in the stomach ? 
 
 [IS-] 
 
 4. How can you tell the difference between a large artery and a 
 
 vein of the same size as seen by dissection in a dead body? 
 What further differences are there between an artery and a 
 vein besides those you can make out by mere dissection? 
 What are the special uses of these differences? [iSO 
 
. . APPENDIX. XUl 
 
 5. What are lacteals and where do they occur? What is iri them 
 
 when an animal is fasting, and what is in them after a meal 
 of mixed food? How are their contents finally passed into 
 the blood? [10.] 
 
 6. How can you show that there is a ' blind spot ' in each of your 
 
 own eyes ? What does the blind spot teach us as to the nature 
 of sight? _ [10.] 
 
 7. What movements can you make with your hand at the wrist -joint ? 
 
 How do the movements you can make with your foot at the 
 ankle-joint differ from those you can make with your hand at 
 the wrist? What are the differences in the joints which cause 
 the difference in the moveinents ? [10.] 
 
 8. What do you understand by a ' reflex action ? ' What structures 
 
 are essential for the occurrence of a reflex action ? Give two 
 or three examples of reflex action as it may- be observed in 
 your own body. What ij the use of reflex actions ? 
 
 [10.] 
 
 9. Of what two parts is the skin composed? What are the more 
 
 obvious and important differences between these two parts? 
 What are the chief uses of the skin to the body ? [10.] 
 
 10. What are the various causes or conditions which make a person 
 
 breathe faster than usual ? What is the exact cause and what 
 is the real use in each case of the faster breathing ? 
 
 [10.] 
 
 11. What is the spinal bulb or medulla oblongata,, and where is it 
 
 placed in the body? What is its form and general appearance ? 
 What are its more important uses? [to.] 
 
XIV ELEMENTARY HUMAN PHYSIOLOGY. 
 
 12. What part of the nose is used for smelling ? What nerve is used 
 for smelling? With what part of the brain is this nerve con- 
 nected, and how does it pass from the brain to the nose ? Why 
 cannot you either smell or taste properly when you have a 
 bad cold in your head ? [10.] 
 
 FIRST STAGE OR ELEMENTARY EXAMINATION, 1895. 
 
 Instructions. — You are permitted to attempt only eight questions. 
 
 The value attached to each question is indicated by the numbers in brackets. 
 
 1. What structures form the walls of the thorax or chest? What 
 
 organs lie inside the thorax ? What movements do the walls 
 make during inspiration, and what movements do they make 
 during expiration ? How are these movements produced ? 
 
 [IS-] 
 
 2. What differences of structure are there between the right and 
 
 left ventricle of a heart? To what differences in action do 
 these differences correspond ? What is the form and structure 
 of the valve between the left auricle and left ventricle, and 
 how does this valve work so as to carry on the circulation of 
 the blood? [iS-] 
 
 3. Where and how is the spinal cord placed in the body? How 
 
 does it end above and how does it end below? What struc- 
 tures are given off at repeated intervals from the spinal cord, 
 and what are the uses of these structures ? [15.] 
 
APPENDIX. XV 
 
 4. What are the essential differences between fats and carbo-hydrates ? 
 Where and how are fats, digested ; where and how are carbo- 
 hydrates digested in the body ? [15.] 
 
 5. Describe- the position and general structure of the liver. What ^ 
 
 is there peculiar about the blood-supply to the liver ? What is 
 the most obvious use of the liver, and what are the arrange- 
 ments by which that use is carried out ? [10.] 
 
 6. What changes can be seen to take place in blood after it is 
 
 drawn off from the body and kept for some time ? What has 
 taken place in the blood to cause these changes which you can 
 see? [10.] 
 
 7. Describe how the skull is attached to the spinal column or back- 
 
 bone, and explain how this attachment enables you to (i) nod 
 your head up and down ; (ii) turn your head from side to 
 side. [10.] 
 
 8. What is the structure of a muscle and its tendon so far as these 
 
 can be made out by careful dissection, without having recourse 
 to a microscope? How are the muscles usually placed and 
 attached to the bones so as to lead to the movements of the 
 body? [I0-] 
 
 9. Of what substance is sweat chiefly composed? By what organs 
 
 other than the skin are some of the constituents of sweat also 
 got rid of from the body ? How does it come about that per- 
 spiration is usually ' insensible,' and what has happened when 
 it becomes 'sensible?' [10.] 
 
 ID. If you cut through a lar^e clot of blood or piece of lean meat, the 
 inside is of a much darker colour than the outside. Explain 
 
XVI ELEMENTARY HUMAN PHYSIOLOGY. 
 
 why there is this difference of colour. What important facts 
 do you learn from the above observations ? [ic] 
 
 II. What is the pupil of the eye? When and by what means does 
 it become smaller, and when does it become larger ? What are 
 ■ the uses of the pupil becoming srtialler and larger ? [lo.] 
 
 12'. If you keep your leg or arm too long in a bent position it often 
 'goes to sleep.' What has happened in your leg or arm 
 when it has thus 'gone to sleep,' and why is it nearly useless 
 to you while in this condition? [lo] 
 
 Edinburgh : 
 Printed by W. & R. Chambers, Limited.