John 3'.''ett . \ FIRST BOOK PHYSIOLOGY FOB THE USE OF SCHOOLS AND FAMILIES, INTENDED AS INTRODUCTORY TO THE LARGER WORK BY THE SAME AUTHOR. BY WORTHINGTON HOOKER, M. D., PROFESSOR OF THE THEORY AB/> PRACTICE OF MEDICINE IN TALE COLLEGE; AUTHOR OF " PHYSICIAN AND PATIENT," " HUMAN PHYSIOLOGY," ETO. ILLUSTRATED BY ENGRAVINGS. NEW YOKE: PRATT, OAKLEY AND COMPANY. NO. 4 CORTLANDT STREET. 1857. b"5 ENTURKD according to Act of Congress, in the Year One Thousand JSferht Hundred and Fifty-five, by WORTHINGTON HOOKER, M. D., in tho Clerk's Office of the District Court of the United States, for the District of Connecticut. JONES & DENYSE, STEREOTYPERS, 183 William-street, New York. PREFACE. THIS book is intended for beginners in the study of Physiology, of whatever age they may be. It is a ". First Book" for the adult as well as for the child. There is more in common between young and adult minds, in regard to a subject which is new to them, than is commonly supposed. There is for both the same need of simple, clear, and precise statement, with familiar illus- tration. A book intended to instruct a child in any science should be so written, that it will be just as instructive to an adult unac- quainted with the subject. Not o'nly so, but it should be so written, that it will interest and please a mind that has a full knowledge of the subject, by its logical and clear development of simple fun- damental facts and principles. It is a common error to suppose, that there need not to be as logical a presentation of a subject in teaching children as in teaching adults. A correct logic, in the true sense of that word, is necessary in either case. In teaching any science, no matter what the age of the scholar may be, a natural, that is, a logical, arrangement of the facts and principles, is essential to success. Indeed, it is more essential at the outset than it is subsequently, for the beginner lays the very foundations of his knowledge, upon which in his course of learning afterwards he builds up the super- structure. It is the simple facts and principles of science, such as should be taught to the beginner, that are fundamental. In order that he may begin right, he must acquire a clear idea of these. 543486 iv PREFACE. This, it is obvious, cannot be done by a loose, partial, and ill- arranged presentation of them, but only by a presentation that is strictly logical. Commonly, this foundation- work, as it may be termed, has to be done over and over again, bringing much unne- cessary labor to both teacher and scholar, simply because it is not done right at the outset. There is another consideration bearing upon this point, which is of great importance. It is essential to the successful study of science that good habits of mind be formed, and the earlier they are formed the better. I need not stop to show that clear logical presentations of facts and principles tend to form such habits, and that a loose, confused mode of presenting them tends to form habits of an opposite character. Let me not be understood to advocate that prominence of logical framework, as it may be -called, which is so common in books for instruction. With all this show of logical arrangement, there is often much that is really very illogical. With the beginner, at least, the less there is of the formalities of arrangement the better. And yet there should in reality be a strict regard to the proper logical order in introducing facts and principles to the mind of the learner. If this natural order be observed, every page that the student learns serves to prepare his mind for what comes after. There is no point in which books for instruction so often fail as in this. Most books for the instruction of beginners in science, present a strange mixture of child's talk, and language that the child cannot understand, but can only learn by rote. Even the hard technical terms of science often enter abundantly into the compound. It seems to be forgotten that great simplicity of language may be the vehicle of even a deep philosophy, and is consistent with an elevated style. Clear, precise statement, logical order of arrange- ment, and felicitous illustration, are the elements of such a style. And these elements cannot exist, unless there be an appreciation in the writer's mind of the attitude of the minds that he addresses. He must not only see clearly the facts and principles of science himself, but he must know how to make others see them clearly also. PREFACE. It is obvious that in a " First Book " there must be a less num- ber of points introduced than in a book intended for instruction afterward. The field of vision should be gradually enlarged as the learner advances. At first there must be a selection of such points as he can most readily understand, reserving the more diffi- cult ones for another book. And while the second book should be much more complete than that which is designed for beginners, yet im the latter the really essential and fundamental parts of the science should be clearly presented. The principles thus advanced I have endeavored to follow in the construction of this little work. It is intended principally for the use of common schools, and yet, like my larger work on Physiology, it is adapted for general reading. It will prepare the reader and the scholar for the more full examination of the subject in the larger work. I need hardly say, that in order to teach from this book satisfac- torily, it is necessary for the teacher to read both books. By doing so. he will see clearly in every case the reason of the selection that I have made in this work from the facts that are presented so fully in the other, and will therefore be better prepared to teach according to the plan that I have in view. The questions that I have placed at the bottom of each page can be altered as the teacher thinks best, to suit the different capacities of his scholars. For certain general directions in teaching Physiology, I refer him to the Ap- pendix of my larger work. CONTENTS. CHAPTER I. THE MACHINES Y OF THE BODY . . . . . . 9 CHAPTER II. THE DIFFERENT STBUCTUKES OF THE BODY ... 14 CHAPTER III. DIGESTION ...' 22 CHAPTER IV. CIRCULATION OF THE BLOOD . . . . . . 86 CHAPTER V. EESPIKATION 64 CHAPTER VI. BUILDING AND KEPAIKINQ . . . . . 74 CHAPTER VII. THE NERVOUS SYSTEM . . 94 CHAPTER VIII. THE BONES . . . . . ' , ... . .107 CHAPTER IX. THE MUSCLES . ... . .... ... . . .180 CHAPTER X. THE EYE . .... . . . . . . 158 CHAPTER XL THE EAK . . . . . . . . . . . .168 CHAPTER XII. CONNECTION OF THE MIND AND BODY . 180 FIRST BOOK IN PHYSIOLOGY. CHAPTER I. THE MACHINERY OF THE BODY. 1. WHEN you look at any machine made by man, you inquire what it is intended to do. You find, com- monly, that it is for some one purpose. Thus, a nail- machine makes nails, and does nothing else ; a paper- machine makes paper ; a locomotive draws cars on a track ; and so of other machines. 2. But the human body is not a single machine for a single purpose. It is a complicated machine, and serves many purposes. It differs very much in this re- spect from the machines that man makes. While for example, it is a machine that walks, walking is not the only thing that it does. It is not like the locomotive, that does nothing but draw cars. It can perform a great variety of motions besides walking. It can run, jump, leap, -climb, &c. 3. You see the same difference, if instead of look- ing at the body as a whole, you look at any particular part of it. Look, for example, at the hand, and com- What is said of machines made by man ? How does the machinery of the body differ from these ? 1* BO.OK IN PHYSIOLOGY. ingenious machinery that man has ever made. The variety of things that it can do is almost endless. So, too, if you open your mouth before a looking-glass, and move about that busy little machine, the tongue, you will get some idea of the great variety of motion that it can perform. 4. But besides being a locomotive machine, capable of all this variety of motion, the human body is also a machine in which many things are made. Blood is made in it. This red fluid is made out of the food which^his machine puts into its mouth and eats. And then from the blood are made all the various parts of the body. 5. In order that the blood may be used to construct all parts of the body, it must be carried everywhere. There is a wonderful set of machinery to do this. The heart is pumping night and day, sending out the blood through the pipes that branch out from it all over the body. 6. Then the blood, when it has been used, is not fit to be used again until it is changed. There is, there- fore, a set of machinery in the chest for the purpose of changing the blood. The blood is carried to the lungs, and there it is exposed to the air that we breathe into the lungs every time that we draw a breath. By being aired in this way, it is fitted to be used again, and it goes back to the heart that it may be pumped out again all over the body. 7. But the most wonderful machinery in the body Mention some particular parts of the body in which this difference is seen. What is made by the machinery of the body ? By what ma- chinery is the blood circulated ? How is the blood changed after it hns been used ? MACHINERY OF THE BODY. 11 is that which we find in the nervous system. The brain is the great central organ of this system. From it branch out white cords, called nerves, which are found in every part of the body. This nervous system is somewhat like a telegraph, though it is much more perfect and mysterious. The brain may be consid- ered as the central office, where the mind has its seat. The nerves may be called the wires, by which mes- sages are sent forth and received by the mind. 8. Messages are sent by means of the nerves to the muscles, whenever the mind wills that any part of the body move. Thus, when you wish to move your hand, messages are sent from the brain to the muscles that move this part. When the mind wills that the whole body shall move, a great number of these mes- sages are sent in all directions at once. 9. The mind too receives messages through the nerves. It receives them from the senses. When we see, something is sent by means of the nerves of the eyes to the brain, and thus reaches the mind, just as electricity goes along the wires of a telegraph. And the same may be said of the other senses. 10. Observe now how great a variety of machinery there is in the body. The digestive machinery grinds up the food with its teeth and mixes it with juices in such a way that blood is made out of it. Then the machinery of the circulation moves the blood about everywhere in the body, so that all the parts may be made out of it and be kept in repair. The breathing What is the most wonderful machinery in the body ? What is it like ? And how ? Describe what is done when the muscles act. How and from what does the mind receive messages ? Give what is stated in Tf 10 about the variety of the machinery in the body. 12 , FIRST BOOK IN PHYSIOLOGY. machinery continually purifies the blood after it has been used, and so fits it again for use. Then by means of the nervous machinery the mind uses the parts that are thus constructed from the blood viz., the mus- cles, the bones, and the organs of the senses. 11. You see that some of the machinery of the body is for the purpose of making other machinery. This is the business of the machinery of the digestion, the circulation, and the respiration. This machinery makes nerves, and muscles, and bones, and the brain, and the eye, and the other organs of the senses. The object then of eating and drinking and breathing and having the blood circulate, is to make machinery for the mind to use. 12. There is one difference between the machinery of the body and the machines constructed by man, that I have not yet mentioned. When man makes a ma- chine he cannot use it till it is completed. If he wishes to alter it or repair it, he cannot use it at all while he is doing this. But the machinery of the l?>dy is constantly altered while it is in use. I will illustrate this difference. 13. The machinery of the child's body is small ma- chinery, but every part of it gradually becomes larger, and in manhood it is of its full size. But no machine made by man can grow to be a larger one. Now, the machinery of the body not only grows, but it is kept in use while it is growing. A small telescope never grows to be a large one, but the little eye of the infant Can the machinery that man makes be kept in use while he is altering or repairing it? How is it with the machinery of the body ? What is said of the growing of the machinery of the body ? MACHINERY OF THE BODY. 13 grows to be the large eye of a man, and is used every day while this is done. A cord does not grow to be a rope, but the muscles grow as we use them. 14. The machines that man constructs cannot be repaired while they are in use ; they have to lie ~by for repair, as it is expressed. It is not so with the ma- chinery of the body ; repairing is going on while it is in use. In the machinery made by man it is done only now and then, but in the machinery of the body it is done all the time, every day, every hour, every moment. 15. One thing is to be noticed, however, about this repairing of the body. Some of its machinery must have seasons of rest, in order that the repairing may be thoroughly done. This is the case with the brain, the nerves, and the muscles. When the mind has worked these parts of the machinery during the day, the rest of night is needed to repair fully the wear and tear. Though the business of repairing them is going on all the time, more of it is done while they are at rest in the hours of sleep than when we are awake. 16. Another thing to be remarked is, that when the machinery is much deranged by disease, more rest than is commonly taken at night is needed. There must be some lying by for repair now. Thus, if a limb be inflamed, it must be kept still. An inflamed eye needs to have the light shut out from it. If the brain be diseased, the mind must be kept from using Does the machinery of the body lie by for repair ? What parts of the machinery of the body must have seasons of rest to have the re- pairing well done ? What is said of the need of rest for repairing in disease ? 14 FIRST BOOK IN PHYSIOLOGY. it as much as is possible ; that is, it must be kept from thinking. And what is true of particular parts of the machinery is true of it as a whole. When the whole body is disordered, as in fever, all the machinery must be kept as quiet as possible. 17. There is some of the machinery that never stops, either when we are sick or when we are asleep ; it is the breathing and the circulating machinery. The heart is always beating, and the chest is always heav- ing ; they never rest from their work, and they are stopped only by death. 18. In this chapter I have given you some general views of the machinery of the body. In the follow- ing chapters I shall describe particular parts of it, and shall explain to you how they operate. I shall speak of the machinery of digestion, of circulation, of respi- ration, the nervous machinery, &c., each of them separately. CHAPTER II. THE DIFFERENT STRUCTURES OF THE BODY. 1. BEFOKE considering each subject particularly, let us look in this chapter at some of the various things or structures that make up the machinery of the body. By doing this, these subjects will be more clear to you. For, as I shall mention different parts of the body, as I proceed, you will understand me better, if you have some knowledge of these parts at the beginning. What parts of the machinery of the body never rest ? DIFFERENT STRUCTURES OF THE BODY. 15 2. Notice first, the hard bones which are the frame- work of the body. These are very different in their shapes in different parts of the frame. For example, in the leg and arm they are long and slender, while in the head they make a box to hold the brain. They vary much in size also. 3. The bones are composed partly of mineral and partly of animal substance. When you see a pile of bones near a slaughter-house, which have been a long time exposed to the air, you see only the mineral part of them. The animal or soft part has been taken away by the heat of the sun and the washing of the rain. The same thing can be done, very quickly, by exposing a bone to a very hot fire. A bone thus deprived of its animal part is very brittle, and breaks easily. 4. The animal part of a bone can be obtained also separate from the mineral part. This can be done by putting it into a mixture of an acid, called muriatic acid, and water. The acid takes the mineral part away, and leaves the animal part in per- fect shape. While the mine- ral part is brittle, this soft animal part can be bent so as FIG. l. What is said of the shapes of the bones, and of their size? Of whal two parts is bone composed ? How can the mineral part be obtained separate from the other part ? How can the animal part be obtained by itself? 16 FIRST BOOK IN PHYSIOLOGY. to be tied into a knot, if the bone be one of the long ones. Fig. 1 represents a thigh-bone thus tied, after being deprived of its mineral part. 5. In the child, when the bones are growing, they do not have as much of the mineral part as the bones of old persons do. It is well that they do not ; for if they did, the frequent falls of the child would often give him a broken bone. If an old person should have as many falls as children commonly do, his brit- tle bones would very often snap asunder. A fall down stairs, which in the child is generally followed only by a momentary fright, a short crying-spell, and perhaps a bruise, is apt to break some bone in the old, and may even destroy life. 6. The bones are bound together by firm ligaments, so that while they move on each other at the joints, they are held in their places. The bones are moved by muscles. The muscles make up the bulk of the fleshy part of the body. Their color is red. The tendons are white and shining cords, by which the muscles pull the bones, in moving them. 7. As I must refer occasionally to the action of muscles before I come to the chapter on the muscles, I will explain to you now the manner in which they act. A muscle is composed of a great number of very small fibres or threads. When it acts, each one of these fibres shortens itself. What is the difference between the bones of the old and those of the young in regard to these two parts ? What would happen to the child if there were not this difference ? By what are the bones bound together ? By what are they moved ? What are the tendons ? What is a muscle composed of? a Fio. 2. FIG. 3. DIFFERENT STRUCTURES OF THE BODY. 17 8. I will show how this shortening of the fibres moves the bones, by means of some figures. Suppose , in Fig. 2, is a bone that is fixed so that it cannot be moved, and that 5 can be moved. Let c be a fibre that extends from the one bone to the other. If the fibre c shorten itself, it will draw the bone ~b towards #, as represented in the lower figure. The same thing is true of a number of fibres, as represented in Fig. 3. You se^, then, how it is true of a multitude of fibres, as they are bound together in a muscle. 9. Let d, in Fig. 4, represent a bone that is fixed, and e a bone that moves on <#, with a hinge-like joint. If the fibres are relaxed, the bone e will be as in Fig. 4 ; but if the fibres contract, the bone will be as in Fig. 5. These two figures show the action of the lower jaw, as it is moved up and down by the muscles, in eating. In Fig. 4, e is like the lower jaw when it is down ; and in Fig. 5 it is like it when it is up, so that its teeth press against those of the fixed upper jaw. FIGS. 4, 5. a r ffi \ ilium Explain by figures 2 and 3, how the fibres of a muscle act Illus- trate the manner in which the muscles move the lower jaw in eating. 18 FIRST BOOK IN PHYSIOLOGY. 10. Figs. 6 and 7 show you how the muscle that bends the elbow acts. In Fig. 6 the bones a and b are represented as they are when the arm is extended out straight. The muscle which is represented by the line c, is relaxed. When it contracts or shortens itself, the bone b will be bent upon #, as seen in Fig. 7. 11. These two examples of muscular action will be sufficient for the present. In some of the succeeding chapters you will see examples of other ways in which the muscles operate ; and, in the chapter on the muscles, the many various ways in which they act will be fully illustrated. 12. I have thus spoken of the bones with their lig- aments, and the muscles with their tendons. The limbs of the body are made up of these four struc- tures. They compose also all the outer parts or walls of the trunk of the body and of the head. Within these walls are the three great cavities of the body, containing its most important organs. 13. In the cavity of the head is the brain. This delicate and soft organ is shut in very securely by that round box of bones, called the cranium or skull. The cavity of the chest contains the heart and the lungs. The walls of this cavity are the spinal column, or back-bone, as it called, the ribs, and the breast- Illustrate the manner in which the muscles bend the arm at the elbow. Of what four structures are the limbs of the body composed ? What other parts do they compose ? DIFFERENT STRUCTURES OF THE BODY. 19 bone. -These are strongly bound together by muscles and ligaments. In the cavity of the abdomen are the stomach, liver, &c. Its walls are the spine behind, and at the sides and in front, broad flat muscles and tendons. The organs contained in these three cavi- ties I shall speak of in other parts of this book. 14:. In all the different structures of the body of which I have spoken, there are blood-vessels, large and small, circulating the blood everywhere. Nerves too go everywhere, branching out from the brain and spinal marrow. They are whitish cords, which by dividing continually are distributed to all parts of the body. The blood-vessels and nerves are everywhere mingled together. For if you prick any part, the nerves feel the pain, and the blood-vessels at the same time let out their blood. 15. All the parts and organs of the body are well packed together. They are so arranged that there is no loss of room. And there is a kind of packing material made use of everywhere between all the parts. It is a very fine and nice material. You can see it if you look at a piece of meat from any animal. If you pull the fibres of the meat a little apart, you will see a delicate white substance between them. You will also see different portions of the meat sepa- rated from each other by considerable layers of this substance. These are the different muscles with the packing material between them. 16. This packing material, which is called the eel- What are the three great cavities of the body ? What are their walls ? What do they contain ? What is said of blood-vessels and nerves in the different structures of the body ? What is said of the packing of the parts of the body ? 20 FIRST BOOK IN PHYSIOLOGY. lular membrane, is not only around all the muscles and between their fibres, but it is around everything and in almost everything in the body. It is full of little cells or spaces ; and hence comes its name. In some parts these cells are larger than in others. The fat of the body is in cells of this substance, mostly just under the skin. When the cells contain fat they are larger than they usually are. 17. This cellular substance is very yielding, so that the motions of the body are not made less free by their being thus bound together by this packing ma- terial. When the muscles are performing some of their motions this substance is very much moved and stretched, but it always yields easily and is not torn. 18. The cells of this substance are kept moist by a very little watery fluid. When this fluid is in greater quantity than it should be, the disease called dropsy is present ; and it is because the cells every- where open into each other, that the water in this disease is so apt to accumulate in the lowest parts of the lower limbs. 19. Over all the parts of the body is the skin cover- ing them up from our view. It also defends them from injury. While for this purpose it is very firm, it is at the same time quite yielding, so that it may not restrain the motions of the body. Underneath the skin the cellular substance is very abundant, con- necting the skin with the muscles and other parts. 20. There is a kind of skin, called the mucous Describe the appearance of the common packing material. What is said of the fat ? What is said of the yielding character of the cellular membrane ? What is said of its cells ? What is said of the skin ? DIFFERENT STRUCTURES OF THE BODY. 21 membrane, that begins in the mouth and nose, and lines all the passages to the lungs, the stomach, and other organs. It may be called the interior skin of the body. It is termed the mucous membrane, be- cause it is moistened by mucus, a glairy fluid which constantly oozes from it. The red covering of the lips does not seem to be either skin or mucous mem- brane, but a texture somewhat like both of them. 21. The serous membranes are so called because they are moistened with a watery fluid called serum. They line the outside of some of the great organs of the body, and also the inside of the walls of the cavi- ties that hold them. Thus the lungs are covered with a serous membrane, and the inside of the walls of the chest is lined with it. You can see what the object of this is : as the chest moves in breathing, the lungs rub a little against the walls of the chest ; but the smooth shining serous membrane that lines them pre- vents the rubbing from doing any harm. The same thing is true of the organs in the abdomen. The rub- bing of the stomach and the intestines against each other and against the walls of the abdomen, would make them sore and inflamed, if they were not all lined with this smooth and moistened membrane. 22. I have not described to you all the structures in the body, but only those that it is well for you to understand in the beginning. You will know more in relation to these as I proceed, and I shall also de- scribe to you in the succeeding chapters some other structures. What is said of the mucous membrane ? "What is said of the red skin of the lips ? What are the serous membranes ? What do they line ? Of what use are they in the chest, and in the abdomen ? 22 FIRST BOOK IN PHYSIOLOGY. CHAPTER III. DIGESTION. 1. I HAVE already told you in the first chapter that the blood, which is the common building material of the body, is made out of the food that we eat. That this may be done, the food must be digested, as it is termed. 2. Digestion is not a single and simple process; several things are done. First, the food is cut and ground by a sort of mill in the mouth ; and while this is going on the food is thoroughly moistened by a liquid called the saliva. As fast as it is ground and moistened it is passed through a tube that extends from the batjk part of the throat down into the stom- ach. There the food is mixed with another liquid called the gastric juice. It is then passed on into the intestines. There all thaj; part of the food that can be used to make blood is sucked up by a multitude of little vessels. These vessels join together to form a tube which empties itself into the blood. Having thus described in a general way the manner in which the nourishing part of our food is separated and extracted from it, let us look at the different parts of the pro- cess more particularly. 3. First, the food is cut and ground up by the teeth. The teeth, in order to be fitted for this work, From what is the blood made ? Is digestion one simple process ? What is jfe| done to the food ? By what is the food moistened ? What is done with it after it is ground and moistened ? What is mixed with the food in the stomach ? Into what does it pass from the stom- ach ? What is done with it in the intestines ? DIGESTION. 23 are made very hard. They are the hardest sub- stances in the body. None of the bones are as hard as they are. Their hardness is owing to the enamel. This forms a thick coat over all the body of the tooth down to the gum. It does not extend down on the roots, for it is not wanted there. The roots and all the inner part of the teeth are like common bone. The roots are fitted into sockets in the jaws so firmly that, as every one knows, it is very hard to pull them out. 4. In Fig. 8 you see a representation of half of the teeth of the upper jaw. Notice the difference in their shape. At a a are the two front cutting teeth. They nave sharp edges. At d d d are the three large back teeth. These have, instead of cutting edges, broad irregular surfaces, so that they can grind the food be- tween them and the same teeth in the lower jaw. At c c are two smaller grinders. At 5 is what is com- monly called the eye-tooth. It is so shaped that it neither cuts nor grinds, but tears. The tooth in the What is said of the teeth ? What is the enamel, and how is it ar- ranged on the teeth ? Describe the different kinds of teeth in man ? 24 FIRST BOOK IN PHYSIOLOGY. FIG. 9. lower jaw that is like it is called the stomach-tooth. You see then that man has three kinds of teeth for eating his different kinds of food, viz., cutting, tear- ing and grinding teeth. 5. Different animals have different kinds of teeth, ac- cording to the kinds of food which they eat. In Fig. 9 you see the teeth of an ani- mal that lives on flesh alone, called a carnivorous animal. The front teeth are tearing ones, while the back teeth have sharp edges for cutting. The flesh is first torn by the front teeth, and then it is cut up by the back ones. You can see these two kinds of teeth in the mouth of the dog. The tearing teeth are long. When the jaws are closed the ends of these teeth do not press upon the ends of the teeth that are opposite to them, but the teeth pass by each other, as you see in Fig. 10, FIG. 10. Describe the teeth of carnivorous animals. What arrangement of their tearing teeth gives them great power ? DIGESTION. 26 Fio. 11. which is a representation of the jaws of a tiger. You see at once that this arrangement of these long tear- ing teeth gives them great power in tearing flesh to pieces. 6. Animals that live on vegetable food, called h#r- frivomus animals, have no tearing teeth. The horse and the cow are of this class. They have two kinds of teeth. There are cutting teeth in front, by which they crop the grass or draw the hay from the rack. There are also grinding teeth by which they grind up the food before they swallow it. In Fig. 11 you see the rough surface of some of these teeth. There is a pecu- liar arrangement of the enamel, which admirably fits them to grind up the fibres of the grass. The enamel is net merely on the outside as it is in our teeth, but there are ridges of it, as you see, standing up in the middle of each tooth. 7. Those animals that live on soft fruits do not need such grinders as the grass-eating animals do. They therefore have rounded teeth which serve to crush their food as repre- sented in Fig. 12. 8. In the cutting, and tearing, and grinding of our food the lower jaw is moved against the upper one by means of muscles. They are the workmen of the mill, as we may say. These muscles work differently Fio. 12. Describe the teeth of herbivorous animals. What peculiar arrange- ment of the enamel do they have ? What are the teeth of animals that eat soft fruits ? 2 26 FIRST BOOK IN PHYSIOLOGY. in different animals, according to the kind of food and according to the character of the teeth. Thus, when an animal eats vegetable food and has grinding teeth, the muscles have the power of making the grinding motion. If it w T ere not so, the grinding teeth could not grind, but could only crush. You can see the difference between the grinding and tearing motion of the jaws, if you watch a dog and a cow while they are eating. The dog, as he tears his food, moves his lower jaw up and down against the upper jaw like a hinge. But the cow, as she chews her cud, gives to her jaw a side wise motion, together with the hinge- like motion, and thus grinds the food. The dog does not need to grind his food as the cow does, and there- fore he has no grinding teeth and no muscles that can perform the grinding motion. 9. Man eats all kinds of food, or is omnivorous ; he therefore has the various kinds of teeth. But ob- serve, that his grinding teeth are not such thorough grinders as the cow and the horse have. He does not need the ridges of enamel to grind the vegetable food that he eats, most of which he softens by cooking it. Observe, too, that his tearing teeth are not so long and so powerful as those that you see in the mouth of the dog and the tiger. The reason is, that he knows how to invent and use cutting instruments, and therefore divides his food very much before he eats it. 10. As the food is cut and ground by the teeth, it Illustrate the difference in the working of the muscles in the carnivor- ous and herbivorous. Why is man called omnivorous? Why are his grinding teeth less powerful than they are in animals? DIGESTION. 27 is well moistened by the fluid in the mouth called the saliva. This fluid is made in some glands in the neighborhood. The largest of these glands, or saliva- factories, as we may call them, is just under the ear. It is this gland that is so much swelled in the disease called mumps. There are three pairs of these glands, and they have ducts or pipes going from them, which open on the inside of the mouth. They are always at work making the saliva to keep the mouth moist, but they are especially busy while we are eating, in order that the food may be properly moistened. 11. All these three pairs of factories do not make the same kind of fluid. One pair make a fluid which is a little thicker than that which is made by the other two pairs. It is curious to see the reason of this dif- ference. The thin fluid is mixed with the food while the mill is grinding it. The thick fluid is not poured out at all while this is going on ; but the moment that we stop chewing, and the food is thrust back into the throat to be swallowed, the thick fluid is poured out and covers the food, so that it may slip down easily into the stomach. 12. The tube through which the food passes down into the stomach is called the oesophagus, or gullet. In Fig. 13 is represented the inside of the stomach with the beginning of the intestines. At 3 is the left end and at 4 is the right end. At 1 is the opening of the gullet into the stomach. At 5 is a valve which is sometimes shut, so as to prevent anything from pass- By what is the saliva made? Where is the largest of these glands situated ? How many of these glands are there ? Are they equally at work all the time ? Do they all secrete the same kind of fluid ? What is the use of the thicker fluid made by one pair of these glands? 28 FIRST BOOK IN PHYSIOLOGY. ing from the stomach into the intestine. This valve is called the pylorus. 13. While the food is in the stomach the gastric juice oozes out from all the inside lining, marked 8, and mixes up with the food. The mixture is very thoroughly made, because the stomach keeps up a sort of churning motion. After awhile the food, although it is sometimes of so many different kinds, is all changed into a greyish cream-like substance, called chyme. 14. None of the food can pass by the valve into the intestines till the gastric juice has acted upon it enough and changed it into chyme. As the stomach churns the food, some of it continually comes in con- tact with the valve. But the valve will not open till some of it comes along that is fit to pass. If the food Describe the stomach as shown in Fig. 13. Where does the gastric juice come from ? How is it mixed thoroughly with the food ? What is the chyme? Describe the operation of the valve called the pylorus. DIGESTION. 29 is not digested, as sometimes happens, then commonly this sentinel after awhile gives up its resistance, and lets the undigested food pass on. Or, if it holds out in its resistance, the food is got rid of b j being thrown back by the stomach through the oesophagus or gullet. 15. When the chyme passes through the valve of the stomach it goes into the intestine, the beginning of which you see in Fig. 13. There two other juices Liver. Pylorus. Pancreas. Stomach. pleen. Large Intestines, mall Intestines. Gall Bladder,- Large Intestines. Beginning of Large Intestines. "Worm-like Appendage. Small Intestines. are poured in and mingled- with it. The duct from the liver is represented in the figure at 6, and the duct Into what does the chyuie pass from the stomach ? What two juices are here mingled with it ? 30 FIRST BOOK IN PHYSIOLOGY. from the pancreas opens near it. These fluids come from two glands. One of these glands is a very large one, the liver. You see this gland in Fig. 14, which gives a general view of the digestive organs. The juice from this gland is called bile. It is of a yellow color and is very bitter. The other juice comes from a gland called the pancreas, which you see in the figure, lying behind the end of the stomach. This is very mild and is much like the saliva with which the food is moistened while the teeth are grinding it. 16. There is a curious arrangement of the bile duct or duct from the liver, which I will notice. "While it goes direct from the liver to the intestine, like the duct from the pancreas, a branch goes back from it to the gall-bladder, as it is called. This arrangement is represented in Fig. 15, in which a is the intestine cut open, b is the duct which is made by the joining together of many little ducts from the liver, c is the gall-blad- der, and d is the duct which goes from the gall-bladder to join the duct from the liver. The object of this arrange- ment is plain. The bile is needed in the intestine in considerable quantity whenever there is chyme there for the bile to act upon. But the liver is a large organ, or a large factory, as we may call it, and is all the time making bile. The gall-bladder is a convenient place of de- posit, or reservoir, where tne bile is stored up until it From what glands do these juices come ? Describe the arrangement of the gall-bladder and the ducts. DIGESTION. 31 is needed. When there is no chyme in the intestine, the bile, as it flows from the liver in the duct J, takes a turn by the branch d into the gall-bladder. In what way it is made to take this sharp turn we do not know. After we have eaten a meal, and the chyme begins to be poured from the stomach into the intes- tine, then much bile is needed, and it comes freely both from the liver and from the gall-bladder. IT. We do not know exactly what the bile and the juice from the pancreas do to the chyme. It is sup- posed that they separate the nourishing part of the chyme from that which is not nourishing, as the chyme passes along through the intestines. As this chyle (so called) is thus separated, it is sucked up or absorbed by vessels scattered all over the inside of the intes- tines. These absorbents are called lacteals, from lac, meaning milk, because the fluid which they absorb is a milk-like fluid. 18. The lacteals are exceedingly small, and cannot be counted. They do their work very faithfully. They will commonly take up nothing but the chyle. Anything else that comes along they shut their mouths against and let it pass on. 19. The chyle is that which makes all the blood. It must therefore in some way be poured into the circu- lation, and I will tell you how this is done. The lit- tle vessels that drink it up from the chyme unite to- gether to form a tube about the size of a quill. This tube runs up in front of the back-bone, and at the top What is the office of the gall-bladder ? What effect do the bile and juice from the pancreas produce upon the chyme? What is the chyle? What are the lacteal*? 32 FIRST BXK IN PHYSIOLOGY. of the chest empties the chyle into the blood where two large veins unite together. And now this whitish milky fluid becomes blood, and is carried every- where to nourish the body. 20. In Fig. 14 you see ell the complicated apparatus or machinery of digestion, except its mill or grinding part where the process begins. The parts are not closely packed together as they are in the body, but they are represented as a little separated from each other, so that you may see them more clearly and fully. As this is a front view the left side of the figure is the right side of the parts. The large encT of the stomach, which is at the right side of the figure, is on the left side in the body. You see that the great bulk of the liver is therefore on the right side. The spleen, which lies against the large end of the stomach, is an organ the use of which we do not understand. Neither does any one know what is the use of the little worm-like appendage at the beginning of the large intestines. 21. The great object of all this apparatus is to ex- tract the chyle, the nutritious part of the food, and pour it into the blood. It is in this way that blood is made out of our food. The blood, the building mate- rial of the body, is all the time used in building and repairing. For this reason there must be a constant fresh supply of blood. It is the chyle poured into the blood by its little tube or duct that gives this sup- ply. If this tube should be cut off, or be blocked up, Describe the way in which the chyle gets into the blood. What does it become? Describe the arrangement of the organs of digestion in Fig. 14. What is the object of all the apparatus of digestion? . DIGESTIO* 33 the blood would constantly lessen, the body would shrink or become emaciated, as we say, and death would at length result. The same thing would hap- pen if the stomach stopped digesting the food, for then no chyle would be formed, and therefore no new blood would be made. 22. There are many things that are very wonderful in all this process of blood-making, which is executed by this complicated machinery of digestion. It is especially wonderful that a simple milky fluid should be separated from, such a great variety of food as we eat from day to day, and then that this whitish fluid should be changed into red blood. 23. The apparatus of ""digestion differs in different animals according to the kinds of food that they eat. If the food that an animal eats is very much like his body, the apparatus or machinery is quite simple ; for the food in this case does not need to be changed much to make his blood. But if the food which an animal lives on is very much unlike his flesh, the apparatus of digestion is very complicated, because the food must be much changed before blood can be made out of it. 24:. For these reasons the digestive machinery in such animals as the dog, the tiger, and the lion, is simple, for they live on flesh, which is of course very much like their own flesh. But in such animals as the cow and the sheep, this machinery is complicated. In what ways can the supply of chyle to the blood be stopped ? What things are there in the process of digestion that are especially wonderful ? In what animals is the machinery of digestion most simple ? In what animals is it complicated ? Illustrate by referring to different 2* 34 FIRST BOOK IN PHYSIOLOGY. The reason is, that the grass which they eat is not at all like their flesh. It must therefore go through a great change to fit it to make the hlood and flesh of such animals. And this cannot he done without con- siderable machinery. The flesh-eating lion has a single stomach, and the length of its intestines is only three times that of its body. But the grass-eating sheep has really four stomachs, and the length of its intestines is twenty -eight times that of its body. Fig. 16 represents the four stomachs of the sheep. In man FIG. 16. (Esophagus Intestine-n Pylorus.^ 4th gtomt 2d gtom ^ lgt gtom> there is but one stomach, and the length of his intes- tines is about six times the length of the body. 25. In birds that eat grains and seeds there is a pe- culiar arrangement of the digestive machinery. They have no teeth, and their mill for grinding their food, instead of being in the mouth, is in the stomach. The gizzard, which is the stomach, is truly a mill for crushing the food to pieces. It has on the inside two How long are the intestines in the lion ? ILI the sheep ? In man ? How many stomachs has the sheep? DIGESTION. 35 very hard surfaces, which are rubbed and pressed together by stout muscles. The grain is thus broken up j ust as it is done between two mill stones. While this is going on the gastric juice comes down from above, and dissolves and digests the broken grain. FIG. 17. This arrangement is seen in Fig. IT, which represents What is there peculiar in the digestive machinery of grain-eating birds? 36 FIRST BOOK IN PHYSIOLOGY. the stomach of a turkey. At I is the gizzard cut open, showing the two hard grinding surfaces, and at a above is the part from which oozes the gastric j uice. In those birds that live on flesh or fish there is no such grinding machinery, but the stomach is a thin bag, just as it is in all animals that live on such food. CHAPTER IV. CIRCULATION OF THE BLOOD. 1. IN the last chapter you saw how the supply of blood is kept up in the body. In this chapter I shall show you how the blood is circulated everywhere, in order that it may be used in building and repairing. The machinery that thus circulates the blood is called the circulating system. It has its pipes everywhere. There is no part of the body where the blood does not go. And this machinery keeps the blood everywhere in motion. It nowhere rests for a single moment. 2. This circulating machinery has a great central organ, the heart, situated in the chest. This forces the blood out all over the body through the arteries. It receives it back again by the veins. It forces the blood out through a large artery, called the aorta, and from this go branches in every direction. These Describe the arrangement of the digestive organs in the turkey. "What kind of stomach have birds that eat flesh or fish? What is the machinery that circulates the blood called ? Is the blood ever still any- where ? What are the different parts of the machinery? Through what does the heart send out the blood ? Through what does it receive it back? CIRCULATION OF THE BLOOD. 37 branches divide more and more, just like the branches of a tree, till the extreme branches are exceedingly small. 3. These small arteries end in a network of vessels that are so small that they are called capillaries, from the Latin word capilla, hair. They are really smaller than any hair. When you prick or cut your finger you wound a large number of these capillaries, and they let out their blood. 4. The heart acts like a forcing and suction pump. It pumps out the blood through the arteries, and by suction it draws the blood back by the veins. It forces out the blood by contracting itself, or making itself smaller. It draws in the blood by dilating itself, or making itself larger. 5. I will make these two actions of the heart plain to you by certain comparisons. When you press the two sides of a pair of bellows together by the handles, as represented in Fig. 18, you contract the bellows FIG. 18. that is, you make the room in it smaller. A part of "What are the capillaries? Like what does the heart act? How does it force out the blood ? And how does it draw it in ? Illustrate by comparison with a pair of bellows. 38 FIRST BOOK IN PHYSIOLOGY. the air is therefore forced out through the nose of the bellows. It is in the same way that the blood is forced out of the heart through the aorta. The only difference is that the heart contracts itself, instead of having it done, as in the case of the bellows, by hands and handles. Again, when you move the handles of the bellows apart, as represented in Fig. 19, you FIG. 19. enlarge the room in the bellows, and so the air rushes in to fill the vacant space. In like manner, when the heart dilates, or enlarges itself, there is more room in it, and the blood rushes in to fill it up. 6. Another comparison, to illustrate the contraction and dilatation of the heart, is this. Fasten a tube to the neck of an india- rubber bottle, and fill it up with water. Put the end of the tube in a vessel of Illustrate the action of the heart by the comparison of the india- rubber bottle. CIRCULATION OF THE BLOOD. 39 water. If now you press the sides of the ball together, some of the water in it is forced out into the vessel, just as blood is forced out through the aorta, when the heart contracts. If now you stop pressing the ball, and let it take its round shape again, the water rushes into it from the vessel. For the same reason, when the heart dilates or becomes larger, the blood rushes into it. 7. I will now explain to you the manner in which the heart contracts and dilates. The heart is made up of muscular fibres, which have the power of short- ening themselves, as you saw in chapter second, 7 and 8. Now suppose one of these fibres, as seen at #, in Fig. 20, shortens itself so as to be like 5, the space that FIG. 20. G is inclosed in it becomes smaller, just as in the case of the bellows. In G and d you see the same thing represented when several fibres are together. If the fibres in c become shorter, so as to be as in c?, the space they inclose is smaller. You readily see from this, that when all the fibres of the heart are short- ened, the space^in it is lessened, and a part of the blood is forced out. 8. You can see by the same figures how the heart Explain by the Figures the action of the muscular fibres of the heart when it contracts and dilates. 40 FIRST BOOK IN PHYSIOLOGY. dilates or enlarges itself. If the contracted or short- ened fibre b lengthens so as to be as 0, the space en- closed by it becomes larger. And so also of any number of fibres. It is supposed that the enlarged or dilated state of the heart is its natural state of rest, when the fibres are not acting, but are quiet. That is, the heart is really at work only when it contracts. When it dilates it merely ceases to act, and lets itself go back to its natural size by its own elasticity, as it is termed. It is just as the india-rubber ball goes back to its natural roundness when you stop press- ing it. 9. The fibres of the heart are not arranged in the regular form in which they are represented in the above figures. They meet each other, and cross each other in various ways. But the effect of their contrac- tion is as described. You can see, for example, by figure 21, that it will make no difference in the effect, whether a single fibre go all around, as in a, or whether two fibres lap on to each other, as in 5, and are fastened together. And the same can be said of any number of fibres. 10. When the heart beats, these fibres shorten themselves, and the blood is forced out into the arte- ries. Then, as the fibres relax, the blood comes into the heart from the veins. And so the heart by turns con tracts and enlarges, just as you contract and enlarge the bellows in working them, as you blow the fire. Is the heart in action, or is it at rest, "when it dilates ? How are the fibres of the heart arranged? Give the comparison made in 10 be- tween the action of these fibres and the action of the bellows. CIRCULATION OF THE BLOOD. 41 11. Let us look now at some things in which the arteries and veins differ from each other. You see veins lying just under the skin in various parts of the body, but you do not see the arteries. They all lie deeper than these veins that you see. The reason is this. It would be dangerous to have the arteries so near the skin as some of the veins are. For the heart is pumping the blood directly into them with great force. And therefore if an artery is cut, it bleeds much more than a vein of the same size, and its bleed- ing is not as easily stopped. For this reason the Maker of our bodies has, as we may say, laid the arteries deep, so that they cannot often be cut in the accidents that happen to us. 12. You can see that special pains are taken in some cases to guard the arteries. Thus the large artery of the arm, when it comes to the joint at the elbow, does not pass over the bones, where it would be apt to get wounded. It lies deep on the inside of the elbow, under the stout tendon that you feel there. So at the knee, the artery is deep in the ham at the back of the joint, in a space between two jutting par- apets of bone, as we may call them. 13. There are only a few places in the body where arteries of any size are very near the surface. In such cases it is because they could not possibly be laid in any better way. One of these is the wrist, where the physician commonly feels the pulse. Another is on the temples. In some persons who are very thin you How do the arteries and the veins differ from each other in their situation? What is the reason of this difference? Mention some cases in which special pains are taken to guard the arteries. 42 FIRST BOOK IN PHYSIOLOGY. can see the artery on the temples beating, and can count the pulse there without being obliged to feel it. 14. As the heart pumps the blood into the arteries with so much force, they are made much stronger than the veins are. If they were not, they would often burst, as you have seen the hose of a fire engine do. But the arteries are made so strong that this is a very uncommon accident. 15. What is called the pulse I will explain to you. When the heart contracts it gives a sudden motion or impulse to all the blood in all the firm arteries. The blood all moves at once. The motion is not like a wave, going from the heart in all directions. The blood at a distance from the heart is moved at the same time with the blood near the heart. It is this motion or impulse that you feel when you put your finger upon an artery. The impulse thus felt is called the pulse. You can feel the pulse wherever you can feel an artery. It is everywhere. In a young infant you can both feel and see the pulse in the open space on top of its head, where the bones are not joined together. This is the pulse of the arteries of the brain. When the heart beats very strongly, as it does in a high fever, this pulse in the brain is very manifest. 16. If a vein be cut, the stream from it is a steady one, because the blood flows in the veins back to the heart slowly and steadily. But if an artery be cut, the stream is not steady but spouts out by jerks or In what places in the body are the arteries very near the surface, and why ? How do the arteries and veins differ in strength, and why ? Explain what the pulse is. Where can you feel the pulse ? CIRCULATION OF THE BLOOD. 43 jets. This is owing to the impulse that is given to the blood in the arteries when the heart beats or con- tracts. There is a jet for every contraction. 17. It is well for every one to know how to stop the bleeding of an artery when it is wounded. It does no good to wind cloths around, as is very commonly done. This only catches the blood, while the artery is left to go on to bleed. If you bear in mind that the blood comes from the heart in the artery, you will see that pressing on the artery on the side of the wound which is towards the heart will stop the bleed- ing. Firm pressure with the thumb will do it if you put the thumb in the right place. In order to find the right place uncover the wound and press your thumb here and there till you see that the blood stops flowing from the wound. If you find that by pressing in any spot the blood is stopped, hold your thumb there till the surgeon comes to take care of the case. If you cannot find the right spot, tie a slip of cloth or a handkerchief around the limb above the wound, and then twist a stick in it till the bleeding stops. A child with this information may be able to save a life, and yet for want of it many a person has died in such a case, for few even among adults understand the matter. 18. The object of the machinery of the circulation is to get the blood into the network of the capillaries, and then bring it back to the heart. It is when the blood is in these capillaries that it is used for building How does the stream of blood from a cut vein differ from the stream from a cut artery ? What is the reason of the difference ? How would you etop the bleeding of an artery I 44 FIRST BOOK IN PHYSIOLOGY. and repairing. It is by the arteries, as you have seen, that the blood is brought to the capillaries, and it is by the veins that it is carried back from them to the heart. 19. As the blood comes from the heart by the arte- ries it has a bright red color. But when it passes from the capillaries into the veins it has a dark color. The cause of this change is the use which is made of the blood while it is in the capillaries. Something has been taken from it for building and repairing, and so it cannot be as good building material as it was before it was used. Not only has there something been taken from it, but there has also been added to it some of the waste matter that comes from the wear and tear of the system. On becoming dark blood, then, it has been changed from good blood to bad blood. 20. This dark blood, then, that goes back by the veins to the heart is not fit to be used so long as it remains dark. When it gets back to the heart it will not do to have it sent all over the body by the arte- ries. It would destroy life everywhere. The organs of all the machinery of the body would stop their operations. For example, if this dark blood should be sent to the brain, the individual would become in- sensible and fall down, and he would die very soon if the good red blood could not be sent to his brain. And so, too, would all the organs stop work, as we may say, if dark blood instead of red were sent to them. What is done with the blood in the capillaries ? What is the color of the blood in the artei-ies ? What in the veins ? What is the cause of the change ? What is done to the blood in the capillaries ? What would happen if the dark blood should be sent to the organs of the body instead of red blood ? CIRCULATION OF THE BLOOD. 45 21. This dark blood then, when it comes back to the heart, must in some way be changed to red blood before the heart sends it again all over the system. For this purpose the heart sends it to the lungs, where, by exposure to the air that we breathe into those organs, it is changed to red blood. After it is thus changed it comes back to the heart, and is then sent all over the body. 22. All this could not be done by the heart if it were a single organ. It is not single. It is double, or rather, there are really two hearts ; one for the circu- lation all over the body, and the other for the circu- lation through the lungs. The two hearts are so closely united together that they are spoken of as one heart. But they are entirely separate, so far as any communication between them is concerned. None of the blood in one can mingle with that in the other. The blood in them is different. In one heart it is red, and in the other it is dark. I shall speak of them as the two sides of the heart, the right and the left side, as is common- ly done. 23. That you may understand the course of the blood in the two circulations, I shall de- scribe it by Figure 22. Let a represent the right side of the heart, c the left side, J the FIG. 22. What is done with the dark blood ? Why is the heart double ? Are the two sides of the heart as separate as if they were two hearts ? Is the blood of the same color in the two sides ? 46 FIRST BOOK IN PHYSIOLOGY. lungs, and d the general system of the body. The arrows point in the direction in which the blood flows. In all the shaded part the blood is dark, and in the part that is not shaded it is red. Let us now begin at some point, and trace the course of the blood. "VYe will start at &, the right side of the heart. The blood received here from the whole body by the veins is of a dark color. It is sent by this right side of the heart to the lungs, ~b. Here it is changed to red blood, and then passes back by veins to the heart but observe, it is to the left side, c. It is now sent by this left side of the heart to the whole system, d. Here, in the capillaries, it is changed to dark blood, and goes back by veins to the right side of the heart, 0, where we started. The blood is constantly going the rounds of these two circulations, day and night, as long as life lasts. 24:. The blood in the right side of the heart, or the heart for the lungs, is dark. The blood in the left side of the heart, or the heart for the whole body, is red. So also in the arteries that go out from the right side of the heart the blood is dark, while that which goes out in the arteries from the left side is red. And while dark blood is brought in the veins to the right side of the heart from the whole body, the veins that come to the left side from the lungs contain red blood. That is, in the circulation for the lungs the dark blood is in arteries and the red in veins, but in the circulation over the whole system it is just the Describe the course of the circulation as represented in Fig. 22. In which side of the heart is the blood red, and in which dark ? How is it in the arteries and veins of the two circulations ? CIRCULATION OF THE BLOOD. 47 reverse the dark blood is in veins and the red is in arteries. 25. The heart is not only two separate hearts, but each of these has two apartments in it. One of these apartments is larger than the other. The smaller apartment is called the auricle and the larger the ventricle. This arrangement is represented in Fig. 23. Fm. 23. The middle part of the figure represents the heart with its two sides, that have no communication with each other ; a being the right auricle, ~b the right ven- tricle, d the left auricle, and e the left ventricle. The blood is received in the right auricle, #, from the general system, f. It then passes into the right ven- tricle, J, and is forced by the contraction of it through arteries to the lungs, c. From the lungs it comes back to the heart, to the left side, and enters the left auri- cle, d. From this it passes into the left ventricle, e, from which it is sent all over the body, repre- sented by/. Describe the apartments of the heart. Describe the circulation as it takes place through these apartments. 48 FIRST BOOK IN PHYSIOLOGY. 26. In each half or side of the heart the ventricle is the main apartment. It is much larger than the auricle. The auricle is a sort of entrance-chamber to the main apartment, the ventricle. There are valves, or folding doors, as we may call them, between these two apartments. These valves are so arranged, that the blood can pass only one way. Take, for example, the valves between the right auricle, a, and the right ventricle, ~b. The blood can go from a to 5, but it cannot go from 5 to a. 27. I will describe to you the manner in which the blood is made to go through these two apartments. When the auricle a dilates or enlarges, it draws in the blood from the veins of the body. It then con- tracts and forces the blood into the ventricle Z>. The ventricle now contracts, and sends the blood towards the lungs, c. Now, when the ventricle ~b contracts, it would force the blood back into the auricle #, as well as forward towards the lungs, were it not for the valves. When the ventricle contracts these valves shut, and so none of the blood can go in that direc- tion, but all of it goes towards the lungs. 28. These valves operate just as the valve of the bel- lows does, as seen in Figures 18 and 19, pp. 37 and 38. In Fig. 19 the hands are drawing the handles apart, and enlarging the space in the bellows. Here the valve is open and the air is rushing in, just as the valves of the ventricle open and the blood rushes in when the ventricle dilates or enlarges. In Fig. 18 How are the valves between these apartments arranged ? Describe the action of the auricles and ventricles. Compare the operation of the valves between them to that of the valve of the bellows as represented in Figs. 18 and 19. CIRCULATION OF THE BLOOD. 49 the hands are pressing the handles together, and the valve is shut, and the air is forced out through the nose ; just as, when the ventricle contracts, the valves close, and the blood is forced out through the artery that goes from the ventricle. Observe now, in what way the valves are shut in both cases. In the case of the bellows, when the handles are pressed together, the air escapes wherever it can. If the bellows are tight, it escapes only through the nose. If the valve does not fit well some of it escapes there. The air, pressing in all directions, shuts down the valve, and if the valve is tight no air can get out there. Now, the blood does in the ventricle of the heart just as the air does in the bellows. When the ventricle contracts, ' the blood, in escaping from the pressure, shuts the valves. If the valves fit well, as they commonly do, none of the blood can go back into the auricle, but it will all go out through the artery, just as all the air goes out through the nose of the bellows, when the bellows are tight. There are other valves in the heart, which, with those that I have spoken of, are fully described in my larger work on Physiology. 29. Having thus described to you the manner in which the blood circulates, I now show you in Fig. 24 a representation of the heart as it really appears. It is a front view. At a is the right auricle. This re- ceives the blood from all parts of the body by two large veins h and i, h bringing the blood from above, and i from below. At 5 is the right ventricle, which receives the blood from the auricle, and sends it to What shuts the valve in the bellows ? What shuts the valveg in the heart? 3 f>0 FIRST BOOK IN PHYSIOLOGY Fio. 24. the lungs by the pulmonary artery f. At c is the left auricle, which receives the blood from the lungs by the pulmonary veins <7, g, g. At d is the left ventri- cle. This receives the blood from the auricle, and forces it out all over the body through the aorta e. The aorta, .as you see, sends off branches upward to the head and arms, and then bends downward behind the heart to send off branches to all the other parts of the body. 30. You observe much irregularity in the arrange- ment of the two sides of the heart, as they are called. Describe the heart as it really appears, by Fig. 24. CIRCULATION OF THE BLOOD. 51 The auricle a and the ventricle & make the right side. The auricle c and the ventricle d make the left side. In this front view of the heart you see only a part of the left side. Much of the left auricle and the left ventricle are hidden behind the right ventricle. The aorta, e, the large artery through which the blood is pumped out by the left ventricle, is at first also behind the right ventricle. 31. The heart, with its four apartments and its four sets of valves, is a very complicated machine. Yet commonly it works well and easily. One part does not interfere with another. All the parts do not work at the same time, and there is a time for each part to act. In this way the whole machine works harmoni- ously. 32. The two auricles act together, and the two ven- tricles act together also. For example, the two ven- tricles contract together, the right ventricle pumping the dark blood into the great artery of the lungs at the same time that the left ventricle pumps the red blood into the aorta, the large artery of the body. 33. The heart, as it works its four parts, the auri- cles and the ventricles, makes two sounds. These you can hear if you put your ear to any one's chest on the left side at its lower part in front. You hear them better here than at any other spot, because the heart here comes so near to the walls of the chest. You hear a heavy and full sound, followed by a quicker What is said of the irregularity in the arrangement of the parts of the heart ? What is said of the complicated character of the heart, and of its harmony in action ? What parts act together ? Where can you best hear the sounds of the heart? Why? Describe its two sounds. 52 FIRST BOOK IN PHYSIOLOGY. and lighter one. The syllables lub-tup are a good representation of these sounds. 34. The heart is almost wholly covered up by the lungs. It is encased in a sack or bag, and around this there is considerable of the common packing material of the body, the cellular membrane, spoken of in the second chapter. In Fig. 25 you see the heart between e f g h the two lungs. The lungs are represented as drawn apart, so that you may have a full view of the heart with its arteries and veins. The sac of the heart and the packing material are also removed. At a is the trachea or windpipe ; on each side are the two arteries that go to the head ; c is the artery that goes to the arm ; 1) *b are the veins coming from the head, and d d the With what is the heart covered ? Describe its situation as represent- ed in Fig. 25, CIRCULATION OF THE BLOOD. 53 veins from the arms, all emptying, as you see, into a large vein that goes to the right auricle of the heart, e ; f is the large vein that brings the blood from below to this auricle ; g is the right ventricle, i the left, and h is the aorta as it goes down from the heart. 35. The heart is commonly about the size of the closed hand of the individual. It is a very powerful organ for so small a one. It is composed of mus- cular fibres, and these are so nicely arranged that each fibre contracts exactly as it should to do its part of the work. 36. The amount of work that the heart does in a lifetime is very great. In an adult it beats about seventy times in a minute. This is over one hundred thousand times in twenty-four hours. In the child it beats much faster than this. And it is to be remem- bered that every time the heart beats each of its four parts contracts and dilates. Each beat of this organ is therefore a complicated movement of a very com- plicated machine. And this machine is always at work as long as life lasts, alike while we are awake and while we are asleep, keeping the blood in motion in all parts of the body. What is the size of the heart ? Of what is it composed ? About how many times does the heart beat in a minute ? How many times in twenty-four hours ? How is it in children ? What is done in the heart in every beat ? Does the heart ever rest from its work ? 64 FIRST BOOK IN PHYSIOLOGY. CHAPTER V. RESPIRATION. 1. You saw in the last chapter that the dark blood is sent to the lungs by the heart in order to be changed into red blood. The great object of the machinery of the respiration is to bring the air and the blood to- gether, so that the air may produce this change. The way in which this machinery operates in doing this I will explain to you in this chapter. 2. The lungs fill up a large part of the chest. They are on each side of the heart, as you have seen in Fig. 25. They are in common language termed the lights; and you can see what they are in man by looking at the lights of other animals. They are spongy bodies. They are full of very small air-cells. These give to them their spongy lightness ; and as a sponge is much larger when its cells are filled with water than when it is dry, so the lungs swell out when their cells are filled with air. This can be shown to you with the lungs of some animal, as a sheep or a calf. If a tube be fastened to the windpipe, you can make the lungs swell out very much by blowing air into them. 3. It is in these air-cells that the air changes the dark blood to red. But this is not done by mixing up the blood with the air in these cells. The blood is never mixed with the air except when in disease What is the object of respiration ? What is the situation of the lungs ? What is the cause of their lightness ? Mention the comparison between the lungs and a sponge. Is the blood mixed with the air in the lungs? RESPIRATION. 55 blood is raised from the lungs. In such a case the blood gets into the air-cells and air-tubes. But in health this never happens. The thin membrane or skin, that makes each air-cell, does not let the blood come through it. The air acts upon the blood through the pores of the skin, and of the capillaries that branch out upon this skin. It is by the airing that the blood thus takes, that every drop of dark blood that goes to the lungs is changed to red blood. 4. The great object of the machinery of respiration is to keep the air going into and out of these air-cells. In this way fresh air is continually brought to the blood. When you breathe in, the air is forced into all these cells ; and when you breathe out, it is forced out of them. It is not all forced out. The lungs are never wholly empty of air. Enough is forced out to keep the air in the lungs constantly changing. 5. Fig. 26 will give you some idea of the structure of the lungs. At d is the left lung, and at c are re- presented the main branches of the windpipe that go to the right lung, separated from the lung itself. At the lower part, at the message can go no further than where the nerves are divided, just as when a telegraph wire is broken, the electricity can go only to the point where it is broken. 9. The nerves are white cords. Each nerve is made up of a great number of tubes. These tubes are so small that they can be seen only by the aid of a very powerful microscope. Each tube is altogether by itself. It is never seen to communicate with any of the other tubes that are bound up with it in the same nerve. Each of these tubes then goes by itself from the brain, where it begins, to the place where it ends in the body. To every separate fibre of any muscle there is probably one of these tubes. This is the telegraphic wire by which the fibre is told by the mind in the brain to act. As each fibre receives a message by itself, whenever the muscle acts, what a multitude of messages are sent to the whole muscle ! 10. Some of the tubes in the nerves are for sensa- tion, and others are for transmitting the messages or impressions to the muscles. These two kinds of tubes are very commonly bound up together in the same nerve to go to any part. And yet they are entirely separate in their office. For example, in the great nerve that goes to the arm, the nervous tubes for the muscles and the tubes for sensation are bound up together. But as the nerve branches out to be dis- o tributed, the two kinds of tubes are separated. And the same tube never transmits sensation to the brain and brings back a message to a fibre or a muscle. .. Of what are the nerves composed ? Do the tubes in them communi- together ? What two kinds of tubes are there in the nervea? D 98 FIRST BOOK IN PHYSIOLOGY. The sensation goes by one set of tubes, and the mes- sages to the fibres of the muscles come by another set. 11. In the body and in the limbs the two kinds of tubes are bound together in the same nerves. But in the face the two kinds of tubes are in two separate sets of nerves. There we have nerves of sensation and nerves of motion separate from each other, while everywhere else they are mingled together. But where they are thus mingled, they are just as sepa- rate in their office as where they are in separate nerves. 12. Here, in Fig. 36, is a representation of the brain and spinal marrow, with the nerves branching out from them in all directions. At a is the cerebrum, the upper large brain filling up a large part of the skull, and at Z> is the cerebellum, the smaller brain lying underneath the cerebrum. You see the spinal marrow extending from the brain down the back. It is very much like the brain in its structure, and should really be considered as an extension of the brain itself. You see that nerves branch out from the brain and the spinal marrow all over the body. 13. You observe that the whole of this nervous system has two exactly similar halves, just as it is with the system of bones, and the system of muscles. The cerebrum has two parts just alike, called the two hemispheres of the brain. So it is with the cere- bellum. There are two sets of nerves also for each half of the body that are just alike. In what parts of the body are these tubes mingled together in the same nerves? Where are they in separate nerves? Describe the arrangement of the nervous system represented in Fig. 36. Is the nervous system single ? What are the hemispheres of the brain ? THE NERVOUS SYSTEM, 99 FIG. 36. 100 FIRST BOOK IN PHYSIOLOGY. 14. In Fig. 37, you see the general arrangement of the brain. It is a view of one of the halves or hem- ispheres of the brain. It is the inside of the hemis- phere that you see. At a l> and c is the cerebrum ; at/ is represented the white substance that joins this hemisphere to the other; at d is the cerebellum, showing a very beautiful arrangement, called the arbor vitce, or tree of life ; at e is the beginning of the spinal marrow ; at g is the beginning of the nerve of sight, and at I is the nerve of smell. Then there are various other nerves, which go to the eye and other parts of the face. 37. Describe the representation of the brain and its nerves, given in Fig. THE NERVOUS SYSTEM. 101 15. Yon observe that the surface of tne' brain 'is very irregular. The brain does not touch the inside of the skull, but it is covered by three different mem- branes, one of which is very strong and^ thick, so as to protect this delicate organ from injury. FIG. 38. 16. The brain is soft, something like blancmange. It is the softest organ in the body. It is composed of two kinds of substance. These are quite well repre- sented in Fig. 38. Here the upper half of the brain is cut off, and you see the upper cut surface of the What is said of the surface of the brain, and of its coverings? is the consistence of the brain ? What 102 FITR&T BOOK IN PHYSIOLOGY. lower half. The outer shaded part is a grayish sub- stance. All on the inside of this is a white substance. You see the dividing line between the two halves or hemispheres. In the middle of the Figure is repre- sented a substance which makes a connection between the hemispheres. It is probably by means of this connection that the two halves of the brain act toge- ther as one brain. 17. It is curious to observe that the white part of the brain is just like the nerves. It is, like them, composed of very fine tubes. It is indeed a great central collection of the beginnings of nerves that branch out all over the bo'dy. 18. The outer gray part of the brain is, on the other hand, made up of cells, instead of tubes. This is sup- posed to be the working part of the brain. The mind acts directly upon the gray part when it moves any of the body. Thus, when you will to have your hand move, the mind does something, but what we know not, to some part of this gray substance. Then an impression or message is sent through those tubes in the white substance which are connected with this part of the gray substance. And as these tubes ex- tend from the brain in the nerves to the muscles of the hand, the hand is moved. 19. In sensation all this is reversed. The impression travels just the contrary way. It goes to the brain, and not from it, as it does in motion. If any one touches you, the impression is carried by the nervous What are the two kinds of substance in the braiu, and how are they arranged ? What is the white substance ? Of what is the gray sub- stance composed ? What is supposed in regard to it? What happens in motion, and what in sensation ? THE NERVOUS SYSTEM. 103 tubes to some portion of the brain. The gray sub- stance at this part of the brain receives the impression from the tubes in the white substance, and so the mind feels it. 20. You observe that I have used the words impres- sion and message in speaking of the communication of the mind, by the nerves, with all parts of the body. I use them because they are the best words that I can use in our present state of knowledge on this subject. We do not know what it is that is sent along the nerves. We only know that something passes through these tubes whenever the mind^feels anything, or ex- cites the muscles to action. And^ n$t knowing what it is, we speak of it as a message or*4^mpression. 21. There have been many supposil^s on this sub- ject. Some have supposed that electricity travels along the nerves just as it does along the wjres of a telegraph. They suppose that it goes from -the brain when the mind excites the muscles to action, and that it goes towards the brain when we feel any sensation. Others have supposed that there was a vibration or shaking of the substance in the tubes of the nerves from one end of them to the other. But these are mere suppositions, and there is no proof that they are true. Whatever it is that passes through the nerves, it must pass through each of the multitude of little tubes separately, for, as you remember, each tube has no communication with any of the other tubes with which it is bound up. 22. Not only are there different nerves for sensa- Do we know what is sent along the nerves ? What has been sup- posed in regard to it ? 104 FIRST BOOK IN PHYSIOLOGY. tion and for motion, as you learned in 10 and 11, but there are also different nerves for different kinds of'sensation. Thus, the nerve that informs the mind of a tickling or a pain in the nose, is not the same nerve that informs the mind of the odors that you smell. The snuff-taker feels the tingling of the snuff with one nerve, and smells it with another. So, too, in the eye, the nerve with which the mind feels a pain there is not the same nerve with which it sees. 23. There are also about the face different nerves for different kinds of motions. Thus, the nerve through which the lower jaw is moved, in eating, is not the same nerve by which the mind works the muscles of the jaw in laughing and in speaking. 24. There mfo organ that has so many different nerves as the eye. It has two different nerves for sensation and four for its various motions. Its ma- chinery of nerves and muscles is therefore very com- plicated. 25. All parts of the body are not equally supplied with nerves. Some parts are very scantily supplied, and therefore have but little feeling, as it is expressed. There are few nerves in the bones, and so when a limb is cut off, the sawing of the bone occasions no pain. There is not much feeling in the muscles, for although they are well supplied with nerves, the tubes in these nerves are the tubes for motion mostly, and few of them are for sensation. The skin has a full What is said in 22 of the different kinds of nerves ? "What is said of the nerves of motion in the face ? What organ has more nerves than any other ? What is said of different parts of the body in regard to their supply of nerves ? THE NERVOUS SYSTEM. 105 supply of the nerves of sensation. In cutting off a limb, therefore, the chief suffering is in dividing the skin. 26. The skin is fully supplied with nerves for two purposes : 1, that it may act as the organ of the sense of touch, and 2, that it may warn of danger. It is, as I have said in another place, a sentinel to guard the organs inside against injury. It feels the least touch. Its nerves at once send their warning of dan- ger to the mind, and the mind sends its orders for action to the muscles, so that the danger may be re- treated from. And as the skin stands guard so faith- fully, there is no need that the muscles and bones and other internal parts should be very sensitive. 27. There is one office of the nerves that I have not mentioned. The different organs of the body sympa- thize "with each other, and it is through the nerves that they do this. Thus, when you have a headache from a disordered stomach, it is because the brain sympathizes with the stomach. When tears flow in grief, it is because the tear-glands are excited to un- usual action through the nerves. The sympathy in this case is with the brain. The sorrowful mind, by its thoughts, affects the brain. Then the tear-glands, by means of the nerves which go from the brain to them, sympathize with it, and so they make and pour forth a flood of tears. 28. There are many actions in the body that result from the connection of different parts by the nerves. For what two purposes is the skin fully supplied with nerves ? "Why is there no need that the muscles and bones should be very sensitive ? By what is the sympathy of the different organs of the body, maintained ? 106 FIRST BOOK IN PHYSIOLOGY. Thus, when there is something in some of the pipes of the lungs, causing an irritation there, we cough in order to throw it off through the windpipe. But the muscles that perform the coughing motion are not in the pipes. They are outside of the lungs in the frame- work of the chest, and remove the irritating substance by forcing the air out against it. JSTow the reason that these muscles are excited to this action is that they are connected by nerves with the pipes where the irritation is felt. So it is in sneezing. If some- thing irritate the lining membrane of the nose, the muscles of the chest throw the air from the lungs with great force up through the nose to expel the offending substance. They could not act in this way if they were not connected by nerves with the lining mem- brane of the nostrils. A message, as we may say, is sent from the irritated spot down to the muscles of the chest through the nerves, telling them to send up a blast of air to expel the intruder. 29. From what I have told you in this chapter in regard to the nerves, you can see that the nervous system is a very complicated system. I have spoken only of those things in it which you can easily under- stand. In my larger work on Physiology I go into this subject much more extensively, and what you have learned in this book will prepare you to under- stand fully what is contained in that. Upon what do many actions in the body depend ? Illustrate by the acts of coughing and sneezing. Jd# w ' ' THE BONES. 107 CHAPTER VIII. THE BONES. 1. THE bones of the body serve many different pur- poses. The three principal of these I will notice. 1. They form the solid framework of the body. In this respect they are to the body what timbers are to a building. 2. Some of the principal bones also form cavities in which important organs are securely in- closed. Thus, the soft delicate brain is made very secure by being inclosed in that round box of bones called the skull or cranium. So, also, the lungs and the heart, as you saw in the chapter on Respiration, are very carefully shut up in a barrel-shaped frame of banes, united firmly by ligaments and muscles. 3. The bones serve another important purpose in being moved by muscles. When they move upon each other at the joints it is the muscles that make them move. The bones are, therefore, a part of the ma- chinery that the mind moves by means of the ner- vous system. This use of the bones shows you why I introduce this subject here. I have told you in Chapter II, 3, of what two substances the bones are composed, and shall, there- fore, say nothing here on that subject. 2. The bones in our bodies are covered up from view by the ligaments, muscles, tendons, and the skin. But this is not so with the skeletons of all animals. Some have their skeletons on the outside of the body. What are the three principal purposes that the bones answer ? Of what two kinds of substance are the bones composed? 108 FIRST BOOK IN PHYSIOLOGY. This is the case, for example, with turtles, crabs and lobsters. With them the skeleton is a coat of mail to defend the soft parts from injury. 3. The bones, although they are so hard, grow together with all the soft parts that surround them. Thus, when the arm of a child grows to be the stout arm of a man, the bones enlarge equally with the muscles, tendons, &c. They enlarge, just as these other parts do, from particles added by the formative vessels from the blood ; for, although they are so hard, the blood circulates in them. 4. The teeth, which are so much like the bones, differ from them in regard to growth. When a tooth first shoots up out of the gum, its body is as large as it ever will be. It cannot grow larger, as the bones do, because the hard enamel can have no circulation in it. If the teeth could grow larger there would be no need of having a second set to take the place of the first. There would then need to be simply an addition of more teeth as the jaw enlarged. But as it is now, all the first set are removed, because they would be too small for the large jaw of the adult, and thirty-two large teeth take the place of the twenty small ones of the first set. 5. The bones are not perfectly solid. They would be too heavy if they were so. Some parts of them are made up of cells, as the large ends of the long bones. The shafts of these bones are hollow. This is for the purpose of making them strong, and at By what are the bones in our bodies covered ? Are they covered up in all animals? "What is said of the growth of bones? How do teeth differ from bones ? Why are there two sets of teeth ? THE BONES 109 FIG. 39. the same time light. In Fig. 39 you see the thigh-bone and the bone of the arm. In both the shaft is hollow, while the large ends are chiefly made up of cells. In birds it is very necessary that the bones should be light while they are strong, so that they may not be burdensome in flying. In them, therefore, the bones are very hollow. They are so for the same reason that the stalks of tall grass and of grain are hollow. If these were solid, and therefore more slender, they would break very easily as the wind bent them over.- And in constructing build- ings, the architect very well knows that a hollow pillar has more strength than the same quantity of wood in a solid form. 6. The bones have a great variety of shapes accord- ing to their different uses. You see this to be true as you look at the skeleton in Fig. 40. In the skull, which holds the brain, you see the bones so shaped and arranged as to form a somewhat round box. At the under part of this box in front are bones of various shapes to accommodate the- organs of four of the Why are the bones not solid ? How are the long bones at their end? "Why are the shafts of these bones hollow ? Why are they very hollow in birds ? What is said of the stalks of plants and the pillars of build ings? 110 FIRST BOOK IN PHYSIOLOGY, FIG. 40. THE BONES. Ill senses, seeing, bearing, tasting and smelling. Then there is the bone of the lower jaw, shaped something like a horse-shoe. The bones of the chest form a bar- rel-shaped cavity for the heart and lungs. The spinal column, Jc, made up of twenty-four bones, extends the whole length of the body as its main pillar. To this are fastened the slender ribs which are joined to the flat breast-bone in front by means of cartilages. The spinal column, you observe, stands firmly supported upon a thick bone which is .wedged in between two broad flaring bones, I and m. This bcfwl-form collec- tion of bones, called the pelvis, supports the contents of the abdomen. You observe the large bones of the thigh and leg, which are made for firmness, and the lighter bones of the upper extremity, which are fitted for quickness and variety of motion. I will now no- tice some of the bones more particularly. 7. In Fig. 41 you see the bones of the head that is, all of them that are in sight in front. There are twenty-two bones in the head, but some of them are out of sight. Fourteen of these be- long to the face. Eight be- long to the cranium, that is, the part of the skull that holds the brain. Of these observe particularly the large bone of the forehead, a, called the frontal bone, the FIG. 41. What is said of the shapes of bones ? Describe the skeleton as rep- resented in Fig. 40. How many bones are there in the head ? How many of them belong to the cranium ? Describe these as seen in Fig. 41. 112 FIRST BOOK IN PHYSIOLOGY. parietal bone, 5, and the temporal bone, or bone of the temples, c. There is a bone in the rear, forming the back of the cranium, as the frontal bone forms the front. These bones, with two others on the under part of the cranium, make the round box that holds the brain. 8. The cranium is made round because it will not break as easily as it would if it were of some other shape. This is one reason also why it is made up of so many different bones, instead of being one solid, tight box. If a blow be received on the head, these bones give a little upon each other, as it is expressed, and so they are not often broken. They give more in the child than in the adult, because, besides being less brittle, they are less tightly put together. It is well that it is so ; for if it were not, the skull would often be fractured, in the frequent falls which the child has. 9. The bones on the top of the head are fastened together by what are called sutures. They are locked together by little teeth of bone, which shoot by each other, as you see in Fig. 42. Here ~b is the suture across the top of the head between the two parietal bones : a a is that between the two parietal bones and the frontal bone in front ; and c c is that between the parietal bones and the bone at the back part of the cranium. In the young child these joinings by suture are not formed, and in the infant the bones are quite apart in some places, especially at the upper part of the forehead, as you can perceive by the touch. Why is the cranium round ? Why is it made of so many bones ? What are the sutures of the skull ? What is said of the joinings of the bones of the skull in the child ? THE BONES. 113 FIG. 42. 10. The bones of the cranium, together with their coverings, are well fitted to guard the delicate brain from injury by the blows to which the head is so much exposed. When a blow is received, its force is broken by the hair, the skin, and the muscles, that extend over the bones. And then the bones them- selves, as I have before said, give a little upon each other. It requires therefore a very hard blow to break the skull. 11. The spinal column is the most wonderful part of the bony machinery of the body, because it serves so many different purposes. It is the great pillar of the body, and yet it is a chain of twenty-four bones, that can be bent considerably, especially in some parts of it. And" besides, there is a canal moving through all this chain of bones, in which lies securely the spinal marrow, an organ as delicate and as essen- Hcw is the delicate brain guarded against injury ? Mention the sev- eral uses of the spinal column ? Of how many vertebrae is it composed I 114 FIRST BOOK IN PHYSIOLOGY. tial to life as the brain itself. Then there are nerves branching out from the spinal marrow, between the twenty-four bones, in such a way that they are never pressed upon. 12. The twenty-four bones of the spinal column are called vertebra, (plural of vertebra.) In Fig. 43, you see one of these vertebrae ; a being the body of the bone; the hole through the vertebra which forms its part of the canal for the spinal marrow ; and c the spinous process, as it is called. The hard ridge that you feel in passing your finger up and down the middle of the back, is the row of these spinous processes. Each ver- tebra has six other processes, only two of which you can see in the figure. The bones of the whole column are so locked together by these processes, that they cannot be separated from each other or dislocated without being broken. In Fig. 44 you have a side view of the same vertebra. As you look at the spinal Describe the vertebrae as represented in Figs. 43 and 44. How many processes or projections has each vertebra ? What is the use of them ? By what are they covered ? THE BONES. column in front, it is a round smooth column ; but in the rear the processes make it very jagged. These are all^however, covered up by muscles, except the row of spinous processes. 13. In Fig. 45, you see the whole col- umn, with the stout bone on which it stands. It is represented as sawn down through its whole length, so that you see but half of it. You see the bodies of the vertebrae in front, and the spinous pro- cesses on the other side. Between the row of the bodies of the vertebrae and the row of spinous processes you see the canal in which lies the spinal marrow. You ob- serve that there are spaces between the bodies of the vertebrae. These spaces are filled with pieces of cartilage or gristle. If it were not for these carti- lages you could not bend the back-bone forward at all, but could only bend your body on the heads of the thigh-bones, with a hinge-like motion, which would be very stiff and awkward. As it is, when you bend forward, in addition to this hinge-like motion, the bodies of all; the vertebrae come nearer together. In doing so the cartilages between them are compressed, and so are made smaller. And as you straighten up again, these cartilages, by their elasticity, return to their usual Describe the spinal column as represented in Fig. 45. Of what use are the cartilages ? 116 FIRST BOOK IN PHYSIOLOGY. size again. From the constant pressure on these car- tilages, as you go about during the day, you are not quite as tall at night as you are in the morning. So also in old age, one becomes less tall than in the vigor of manhood, because these cartilages shrink. 14. The spinal column can be bent not only for- wards, but in other directions also to either side and backwards. This chain of bones can also be some- what twisted, as we may express it, as you turn your body one way and another. As you do this, each bone moves with a rotary motion a very little. But as there are twenty-four bones, all these little motions between them together make a considerable twist of the whole column. Now, as there is through the whole length of this column a rod of very delicate substance that must not be pressed upon, all these motions have to be most carefully arranged. The bones must be nicely fitted with all their processes ; they must be well fastened together with ligaments ; and then the muscles that move all these twenty-four bones must all of them work exactly aright. All this is done, and the back-bone, as we call it, is a set of machinery vastly more complicated and more nicely arranged than any machinery that man ever con- trived. 15. But the most wonderful part of this machinery is at the top of the column. There the motions are more free than in any other part of the column, as you see when you bow your head, and bend and turn In what part of the day are you the tallest ? What is said of the various motions of the spine ? What is said of it as a piece of machine- ry ? What is the most wonderful part of this machinery ? THE BONES. 117. it in various directions. There are two different mo- tions made by the head on the top of the column. The first of" these is when you move the head back- ward and forward. In doing this it rocks on the first vertebra, the topmost bone of the spinal column. For this purpose there are two smooth rounded sur- faces, that work in two smooth, hollow places in the vertebra. 16. The other motion is when you turn your head to look at the one side or the other. In performing this rotary motion the skull does not move alone, as in the first motion, but it moves together with the first vertebra. The first vertebra in this motion moves on the second around a tooth-like process that stands up from this second vertebra. This tooth works in a smooth notch on the inside of the first ver- tebra. It is bound very fast in this notch by a strong ligament, so that it may not, in any of the quick mo- tions of the head, be made to press FIG. 45. on the delicate spinal marrow which lies against it. In Fig. 46 you see these two vertebrae, and notice the tooth-like process of the second standing up on the inside of the first vertebra. 17. You see, then, that when you move your head backward and forward, you move it in a hinge-like way on the first bone of the spine ; and when you turn the head to look to the right or the left, you How many motions are performed by the head on the top of the spinal column ? Describe the manner in which the first of these motions is performed. Then the second. 118 FIRST BOOK IN PHYSIOLOGY. turn the head and this first bone together as one thing on the tooth-like process of the second bone. There is an arrangement somewhat like this in the standard of telescopes. There is first a hinge-joint, as in the case of the head, so that you can move 'the telescope up and down so as to look as high or as low as you wish. There is, also, in the standard another joint, with a rotary motion, by which you can turn the telescope so as to see as far to the one side or to the other as you please. This is like the motion per- formed between the first and second vertebra. 18. The vertebrae vary much in different kinds of animals. Here, for example, in Fig. 47, is the verte- bra of a fish, which you see differs very much from the vertebrae of man, as represented in Figs. 43 and 44. It has but two processes, ff. In man there is a iiG.47. single short spinous process behind, wiiile the vertebra is round in front. But in the fish there are two quite long spinous pro- cesses, one in front and the other in the rear ; or rather, we should say, according to the common position of the fish in the water, one above and the other below. There is a curious contrivance in the ar- rangement of the vertebrse of the fish for making the spine flexible. Each vertebra has a cup- like cavity on each side towards the next vertebra. Each two vertebrse then put together make a cavity of this \ shape. This cavity is lined with a Give the comparison between this arrangement and that of a stand- ard of a telescope. Describe the vertebrse of a fish and their arrange- ment. THE BONES. H9 membrane making a sac, and in this is a fluid some- thing like the white of an egg. These sacs, thus filled with fluid, make soft cushions between all the bones of the spine, upon which the bones rock in the various motions of the fish. This arrangement you can observe for yourself whenever you have fish on the table. 19. In snakes the spinal column is exceedingly flexible. It is made so in two ways. First, there is a great number of vertebrae. The result of this is, that in a very extensive motion of the whole spine the motion between each two vertebras is very little. The motion is divided up, as we say. The rattlesnake has over two hundred vertebras, and the great boa- constrictor has three hundred and four. Secondly, the flexibility of the spine of these animals is secured by having a ball and socket joint between all the ver- tebras. A smooth round ball in each vertebra works in an equally smooth cup-like hole in the one next to it. 20. The framework of the chest I have described to you in the chapter on Kespiration 10. There are two bones outside of this barrel-shaped framework that I will now notice. First, there is the collar-bone <7, Fig. 40. This is fastened to the breast-bone at one end, and at the other end is fastened to a process 'of the shoulder-blade, and helps to make the top of the shoulder. It is a sort of prop or brace, that keeps the shoulder braced out in its place. By what two means are the spinal columns of snakes made so flexi- ble ? How many vertebrae has the rattle-snake ? How many has the boa-constrictor ? What is the use of the collar-bone, and how is it placed ? 120 FIRST BOOK IN PHYSIOLOGY. 21. The shoulder-blade is a very singular bone. Its back part, that which is towards the spine, is quite thin, and is covered on both sides with muscles that move it. It is designed to give freedom to the mo- tions of the arm. "When you draw your arm back very much, you can see that there is considerable mo- tion of the shoulder-blade. This is because the mus- cles that are attached to it pull it back, at the same time that other muscles pull the arm in the same direction. And as the shoulder-blade forms at its upper part the shoulder-joint, these muscles in pulling back the bone pull back the whole joint, and of course the arm with it. You can see that the arm could not be drawn so far back if the shoulder-joint were made without any shoulder-blade. It could have been so made, but it would have been awkward and stiff in its motions. 22. Where the shoulder-blade forms the shoulder- joint there is a shallow cup-like surface, lined with cartilage, which is as smooth as the finest polished ivory. The bone of the arm which fits into it has its end in the form of a ball, which is also tipped with cartilage as smooth as that in the cup. Observe what keeps this ball in the cup as it moves about in it. There is a thick skin attached all around the edge of the cup and fastened down over the ball. Besides this stout ligament, there is another remarkable con- trivance for keeping the round head of the bone in its place. The tendon of a large muscle works in a Describe the arrangement of the shoulder-blade. How does it make the motions of the arm free ? Describe the shoulder-joint. In what two ways ia the joint guarded against dislocation? THE BONES. 121 groove on the front of this head of the bone, and thus holds it so as to keep it from slipping out of the cup. 23. It is Necessary that the joint should be thus carefully guarded, because the cup or socket is so shallow. As it is, although it is so well guarded, it is very often dislocated. It might have been made more secure by having the socket deeper ; but then the motions of the arm could not be as free as they are now, and freedom of motion you can readily see is very important in this part of the machinery of the body. 24:. The arm-bone, i, Fig. 40, is jointed at the elbow, with the two bones of the fore-arm (so called) and seen at o and n. The elbow-joint is different alto- gether from the joint at the shoulder, for the motion is in one direction only, back and forth like a hinge. It is therefore called a hinge-joint, while that at the shoulder is called a ball-and-socket-joint. In whirling a skipping-rope, you use the joint at the shoulder; but in striking with a hammer, you use the hinge-joint at the elbow. 25. The hand moves on the fore-arm at the wrist with a hinge-joint. The fingers have hinge-joints, except where they are joined to the hand. There they have, besides the hinge-like motion, something of the motion of a ball-and-socket-joint. The motions of the thumb are, as you see, quite different in some respects from those of the fingers. Why is this joint so carefully guarded ? How could it have been made more secure? Why was it not? Describe the elbow-joint. How does it differ from the shoulder-joint ? Describe the joints of the wrist aud fingers and thumb. 6 122 FIRST BOOK IN PHYSIOLOGY. 26. Besides these mo- tions that I have descri- bed, there is a rotat^y motion of the arm, as you turn the palm of the hand up and down. This is done by a pecu- liar motion of the two bones of the fore-arm. I will make this clear to you by Fig. 48. You see that the largest end of the ulna, a, is at the elbow, while the largest end of the radius, 5, is at the wrist. Now, the hinge-like motion at the wrist is performed whol- ly with the large end of the radius. The small end of the ulna, marked #, has nothing to do with it, but is loose, and has a rolling motion on the end of the radius. It is just the reverse with these two bones at the elbow-joint. The hinge-motion there is per- formed with the large end of the ulna, a, and the small end of the radius, ~b has nothing to do with it, but rolls on the end of the ulna. 27. The effect of this arrangement is this. When the palm of the hand is upward, as represented in the How is the rotary motion of the fore-arm made? THE BONES. 123 Figure, these two bones are, as you see, nearly paral- lel. But when the palm is turned over, they are, as we may say, twisted upon each other, the ulna, #, roll- ing on 5, at its lower end, and the radius, , rolling on #, at its upper end. You can see these two positions of these bones in Fig. 40. In the right arm you see the palm of the hand towards you, and the radius and ulna are parallel. In the left arm the palm is partly turned from you, and these bones are twisted upon each other by their rolling or rotary motion. 28. Observe now how many different motions there are in the arm and hand. * They are, the motion of the ball-and-socket-joint at the shoulder, the hinge-motion at the elbow, the rolling of the two bones at the fore- arm upon each other, the hinge-motion at the wrist, the hinge-motions of the fingers at their joinings with the hand, together with something of a ball-and-socket- motion, the hinge-motions of the other joints of the fingers, and the free motions of the thumb differing somewhat from those of the fingers. 29. In observing these motions you will see the rea- son why there are different kinds of motion in differ- ent parts of this complicated machinery. You can see, for example, why there is a hinge-motion in one place and that of a ball-and-socket joint in another, and why the two motions are united in the joints which the fingers make with the hand, while the other joints of the fingers can perform only the hinge- motion. Mention the different motions of the arm and hand in their order, be- ginning at the shoulder-joint. What is said of the two kinds of motion, the hinge-like and the ball-and-socket-motion ? 124 FIRST BOOK IN PHYSIOLOGY. FlG - 49 - 30. You see that there are many bones in the hand twenty -seven in all. There are eight small bones called the carpal bones, represented at d, in Fig. 48. These are tightly packed together, and lie next to the bones of the fore-arm. The metacarpal bones, those that bind them at their ends, where the bones of the fingers are jointed with them. At a, , c, and fe|^^^ skill and power appear vastly more wonderful, when w r e think of the eye of a mere common insect, as made up of thousands of optical instruments, each, though so minute, being more perfect than any instruments that man can make. CHAPTER XI. THE EAR. 1. THE mind acquires the knowledge of sounds by the apparatus of hearing. This apparatus is very complicated, and some of it is exceedingly delicate. Before describing it I will say something of sound, in order that you may better understand the operation of this apparatus. 2. Sound is caused by a vibration or shaking of some substance. You can perceive this vibration in a bell if you touch it after it has been struck. If the bell is quite large you can see as well as feel the vibration. You can see it in the string of a piano or a violin. It is the vibration of the cords in the larynx that produces the sound of the voice. It is not solid bodies alone that produce sound by their vibration. Why are the compound eyes of insects more wonderful than the hu- man eye ? How is sound produced ? Give examples of sound made by the vibration of air ? THE EAR. 169 It is often produced by the vibration of the air. This is the case in whistling. In the flute it is the vibra- tion of the air in the instrument that produces the sound. And so of other similar instruments. 3. When the vibrations are equal, the sound is a musical one. But when they are irregular, the sound is a noise, that is, a confused sound. 4. Sound passes through the air by vibrations. It may be said to pass by waves in all directions, just as waves go in all directions on the surface of water when a stone is dropped into it. And as these waves in the water lessen as they extend from the spot where they begin, so the waves of sound lessen the farther they are from where the sound is produced. That is, the sound dies away in the distance, as it is expressed. 5. That sound is transmitted in this way through the air can be proved by experiment. If a bell be set to ringing under the glass receiver of an air-pump, as you pump the air out of the receiver, the sound of the bell becomes more and more faint, till at length you cannot hear it at all. The reason is, that the vibra- tions of the air lessen as the air itself lessens and be- comes thin ; and when the air is all pumped out, there are no vibrations to convey the sound of the bell. So, too, sounds made on the top of a very high mountain are not as loud as when made in the valley below, because the air at so great a height is very thin. What makes the difference between a musical sound and a noise ? How does sound pass through the air ? Give the comparison in regard to the diffusion of sound. How can you prove that sound passes through air by vibrations ? 8 170 FIRST BOOK IN PHYSIOLOGY. 6. Other substances besides air transmit the vibra- tions or motions of sound. If you put your head un- der water, and let some one strike two stones together under the water at some distance from you, you will hear the sound. That is, the vibration will come to your ear through the water. If you place a watch between your teeth, you hear its ticking quite as dis- tinctly as when you put it to your ear. In this case the vibration goes to the nerve of hearing by the teeth and the bones, and does not go round by the air into the tube of the ear. 7. The vibration of sound passes more readily through solids than through the air. If you put your ear upon the end of a long log you can hear the scratch of a pin made at the other end. And yet you cannot hear it through the air at the distance of only a few feet. A deaf gentleman, as he rested the bowl of his long pipe upon his daughter's piano, found that he could hear the music much more distinctly than he could through the air. In this case the vibration went through the pipe to the teeth, and then through the bone to the nerve of hearing. 8. The vibrations or waves of sound are reflected by objects against which they strike. For this reason a sound can be heard further along a wall than in an open field. If one speaks in an open field, the sound is scattered in all directions. But the wall keeps it from being thus scattered. For the same reason, a Illustrate the fact that other substances besides air transmit the vi- brations of sound, What is said of the transmission^ sound through solids compared with its transmission through air ? Illustrate in vari- ous ways the reflection of sound. THE EAR. 171 speaker can be better heard in a building than in the open air. In this case the walls shut in the waves of sound. So, also, a speaker can be heard better when the ceiling is low than when it is very high. When the ceiling is high much of the sound of the voice is lost in the space above. In a speaking-tube, even a whisper can be heard at a great distance, because the waves of sound are so shut in by the tube. 9. In hearing, the waves of sound are caught by the outer ear, as it is called, and they go into the tube which you see there. The purpose of this outer ear is to collect these vibrations and direct them into this tube. It is well shaped on the whole for this purpose, but the ridges and prominences that you see on it do not render any assistance in this respect. They merely serve to make the ear a comely organ. Some animals have ears which answer much better in col- lecting the waves of sound than the ear of man does, because they need them. Man could hear more easily if his ears were larger, and were shaped more like the open end of a trumpet, but such ill-looking appendages are not necessary in his case. He some- times assists the ear in collecting the vibrations of sound by putting his hand up behind it. Yery deaf persons often use an ear-trumpet. The broad trumpet- shaped end is turned towards the speaker, so as to catch the waves of sound and direct them into the tube of the ear by the pipe of the instrument. 10. The vibrations of sound in the air, entering the "What is the purpose of the outer ear ? What is said of its shape, and the irregularities on its surface ? What is said of the ears of some animals ? In what way is the ear sometimes assisted ? 172 FIRST BOOK IN PHYSIOLOGY. tube of the ear, strike upon a drum at the end of the tube. This drum of the ear is a membrane fastened to the bone, just as the drum-head of a common drum is fastened to its wooden rim. The vibrations that thus enter this tube as they strike the drum make it to vibrate. 11. The vibration does not stop here. It is commu- nicated to a chain of little bones on the other side of the drum. The farther one of this chain of bones rests on another membrane or drum. The vibration is therefore communicated to this second drum. And this drum covers an opening into some winding pas- sages in solid bone. These passages are filled with a fluid, and the vibration of the drum over the opening makes this fluid to vibrate or shake. 12. The fine delicate fibres of the nerve of hearing are in the midst of the fluid in the winding passages. They feel the vibration of the fluid there, and an im- pression goes by them through the trunk of the nerve to the brain, and is received there by the mind. And this completes the process of hearing. These winding passages, where the nervous fibres are at their post ready to feel the vibrations that come there, are the real halls of audience, as we may call them. I will now describe some of these parts more particularly. 13. The little bones in the ear are four in number. They are connected together, and are commonly spoken of as a chain of bones. In Fig. 72 they are re- Upon what do the waves of sound entering the ear strike ? Trace the transmission of the vibration inward from the drum of the ear. Where are the fibres of the nerve of hearing, and how are they affected ? What completes the process of hearing ? THE EAR. 173 presented separate and considerably magnified, so that you can see their shape distinctly. They are named from their shapes. They are the hammer, m; the anvil, i / the round bone, o, the smallest bone in the body ; and the stirrup, s. The Flo . 72 . long handle of the hammer, h, is fastened to the middle of the drum of the ear, and its blunt end fits on to the anvil. The little round bone is fixed between the slender end of the anvil and the top of the stirrup. And the bottom of the stirrup presses upon the second drum of the ear. In Fig. 73 you have a repre- FIG. 73. sentation of these bones, together with the drum of the ear. When the vibra- tion of sound comes to these bones, the hammer receives it first and it passes to the anvil, then to the little round bone, then to the stirrup, which communicates to the drum that is over the opening to the winding passages. 14. In Fig. 73 is represented, much magnified, the shape of the winding passages, which I have told you are in solid bone. The middle part of it, v, is the vestibule, or common hall of entrance to the passages. From this go out on the upper side the semi-circular canals, x, y, z, and on the lower side the passages of the cochlea, k. At o is the opening into the vestibule Describe the little bones of the ear. In what order does the vibra- tion of a sound pass through this chain of bones ? Describe the winding 174 FIRST BOOK IN PHYSIOLOGY. FIG that is covered by the se- cond drum. This drum, you will remember, is pressed upon by the stirrup-bone. -At r is another opening, which is also covered by a membrane or drum. The cochlea is called so because it is shaped like a snail's shell. It is most curiously arranged, having two spi- ral passages, each taking two turns and a half around a pillar in the middle. This part of the ear represented iii this figure is called the labyrinth, because the winding passages are so complicated. 15. Having thus noticed the different parts of the apparatus of hearing, let us look at it altogether, as represented in a map of it in Fig. 75. At a 1) c is the external ear ; at d is the entrance to the tube of the ear/; at g is the drum of the ear. At h is the cavity beyond the drum where the chain of bones is, the bones being left out that the arrangement of the appa- ratus may be more clear to you. At Jc is a tube which comes from the back part of the throat to this cavity. If you shut your mouth and close the nostrils with your fingers, and then force the air strongly from your chest into the mouth, you can feel the air pass through this tube into the ear where the little bones are. At I is the vestibule of the labyrinth ; at Why are the winding passages called the labyrinth ? Describe the various parts of the ear as represented in Fig. 75. THE EAR. 175 FIG. 75. 71 m are the semi-circular canals ; at n is the cochlea ; at o is the trunk of the nerve of hearing as it goes to branch out in the labyrinth ; and at e e is the bone in which the labyrinth is inclosed. 16. I will now describe to you the process of hear- ing, tracing its successive steps by means of the map of the apparatus. The vibrations or waves of sound go into the tube of the ear, df> and strike on the drum, <7, making it to vibrate. This vibration is communi- cated to the chain of bones in the cavity, h. The last bone in vibrating shakes the little drum that co- vers the opening into the winding passages, I in n. This sends a vibration throughout the fluid in all these Trace the process of hearing in its successive steps on this map of the apparatus. 176 FIRST BOOK IN PHYSIOLOGY. passages. The nervous fibres scattered through this fluid feel the vibration, and the trunk of the nerve, o, passes on the impression to the mind in the brain. 17. Observe that there are five different vibrations in succession before the nerve of the ear is reached the vibration of the air, in the tube of the ear, / of the drum, g of the chain of bones in the cavity, h of the little drum over the opening into the winding passages and lastly, of the fluid in these passages. Every time that a sound is heard, these vibrations fol- low each other, in the order that I have mentioned. It seems a long process, as it is described, but it takes but an instant. And in hearing one speak, how rap- idly does one vibration follow another, and yet how distinct the different vibrations are as one sound suc- ceeds another. The successive vibrations can be exceedingly rapid, and yet be entirely distinct. You can observe this in the rapid strokes of some kinds of machinery. You can observe it also, as you strike as rapidly as you can with a stick upon anything. For every blow of the stick you have the succession of vibrations that I spoke of in the first part of this par- agraph. And you cannot strike fast enough to make the vibrations mingle together. 18. I have described hearing as it commonly occurs. But, as I have already told you in 6, sounds do not always go in through the tube of the ear. They sometimes get to the winding passages by another way; as for example, the sound of the watch How many different vibrations are there for every sound ? What is said of the distinctness and rapidity of the vibrations as they follow each other ? THE EAR. 177 when placed between the teeth. In such a case, there are not so many changes in the vibration as when we hear in the common way. There are only three vibrations to follow each other for every sound, viz., the vibration of the teeth, that of the bones between the teeth and the winding passages of the ear, and that of the fluid in these passages. 19. You see, then, by such cases that there can be hearing without using the drum of the ear or the chain of bones. Indeed these parts may be destroyed, and yet if the winding passages are not at all injured, the person can hear, though of course hot as well as when the apparatus is all there. The winding pas- sages, the halls of audience, as I have called them, are then really the essential part of the apparatus. And so long as the vibration of sound can in any way reach the fluid in them, and shake it so that the fibres of the nerve shall feel it, there will be hearing. But if the fluid be in any way let out of these passages there will be no hearing, although the drum of the ear and the chain of bones may be in perfect order, and may vibrate regularly to the sounds that come into the tube of the ear. The vibration in this case will stop at the stirrup-bone, and will not reach the nerve. 20. This innermost and most important part of the apparatus is very securely guarded from injury. The winding passages are inclosed in the hardest bone in the body. It is so hard that it is called the petrous or rock-like bone. May sounds be beard in some otber way tban tbrougb tbe tube of the ear ? What is the most important part of the apparatus of hearing ? Explain in full. How are tbe winding passages guarded from injury ? 8* 178 FIRST BOOK IN PHYSIOLOGY. 21. The outer passage into the ear is well guarded, and in rather a singular way. Besides the hairs that are in the tube, which serve to catch particles that may fly in, there is also a waxy substance secreted there. And this substance, though it is so different from anything else in the body, is, like everything else, made from the blood. It is made by some very small glands situated in the lining of the tube. It is very bitter, and the odor of it serves to keep out small insects which might otherwise creep or fly in. It answers this purpose so well, that although the tube is. always open, it is quite uncommon to have an insect get into the ear. And when one does, it becomes so enveloped in the wax that its struggles can do but lit- tle harm. Commonly the insect soon dies perhaps, in part, from the bitter dose which he is obliged to take. 22. I have thus, in this and the previous chapter, treated quite fully of two of the senses. Of the other senses I have spoken incidentally in other parts of the book. The organs of the different senses differ from each other, as they are fitted to inform the mind of the different qualities of things around it. For exam- ple, the organ of smell is very different from the organ of hearing. Fine particles pass from bodies that give out an odor ; and these, coming in contact with the nerve spread out in the nose, make an im- pression, which is transmitted by the nerve to- the brain. But in hearing, no particles from the sound- ing body come in contact with the nerve. A mere shaking or vibration goes through the air to the drum How is the tube of the ear guarded ? Give the difference stated between the organ of smell and that of hearing ? THE EAR. 179 of the ear, and is passed on from this through the chain of bones to the fluid that surrounds the fibres of the nerve of hearing. 23. In the sense of taste, the particles of the sub- stance tasted are commonly applied in a coarser way to the nerve than in the sense of smell. In the sense of touch, the substances do not, as in smell and taste, come into actual contact with the nerves. They are felt through the cuticle ; for this, as I have told you in 28, Chapter YL, is not sensitive at all ; that is, it has no nerves, but is only a soft delicate covering to the very sensitive true-skin. 24. In regard to the sense of sight, we know not what it is that enters the eye and pictures the images of things on the retina. Light is now generally sup- posed to be a^ vibration of an exceedingly fine sub- stance, finer than air, which is thought to exist every- where. The vibration of this substance, which is called ether, is thought to be like the vibration of air in sound. Like that, it goes in waves, in all direc- tions, from where it begins. If light and sound are thus only motions, they are in some respects dif- ferent motions. They never interfere with each other, though they are continually mingled together, and cross each other in all directions. They differ in one respect very much. Light is a much faster vibra- tion than sound. If you look at a cannon fired at a distance, the flash comes to your eye much sooner than the sound comes to your ear. The same is true also "of the flash of lightning and its sound, the thunder. What is said of the sense of taste? What of the sense of touch? What is light supposed to be? What is said of the vibrations of light and sound ? 180 FIRST BOOK IN PHYSIOLOGY. CHAPTER XII. CONNECTION OF THE MIND AND BODY. I HAVE already said much of the connection of the mind and the body. I showed you in the chapter on the Nervous System that this connection is main- tained by means of the brain and the nerves. You there learned, that all the knowledge which the mind gets of the world around it comes from the senses by means of the nerves ; and also that the only way in which the mind communicates its knowledge to others is by means of the nerves that excite the muscles to action. In the chapters following that on the Ner- vous System, we considered the instruments by which the brain and nerves operate in thus connecting the mind with the world around it. These instruments are the muscles and bones, and the organs of the senses, the eye, the ear, the nose, the mouth, and the skin. In this chapter I wish to carry you on a little farther, and show you more than I have yet done in regard to the manner in which the mind uses these instruments by means of the nerves. 2. The mind is connected with every part of the body. It therefore feels what is done to any part, and it can move the muscles everywhere by willing to have them moved. But the mind, though it is con- nected with every part, is not in every part. If you pinch your finger the mind feels it as readily as if it Give the summary, in 1, of what has been already said in regard to the connection of the mind and the body. How do you know that the mind is connected with every part of the body ? CONNECTION OF THE MIND AND BODY. 181 were itself in the finger. So, also, it can move the finger as easily as if it were really there among the muscles. But if the hand be palsied, feeling and mo- tion are gone in the part ; and yet the mind may be active, and move other parts that are not palsied, and feel what is done to them. 3. The mind, then, is not, as life is, all over the body. It is in the brain. This is its central office, the nerves being its communicating wires. We seem to know very early in life that the mind is in the brain. The child is conscious that he does his think- ing in his head. But besides this consciousness, we know some facts that prove that the mind resides in the brain. Thus, if a man be knocked down senseless by a blow on his head, the mind feels nothing, and can move no part, because the mind's organ, the brain, is so much affected by the blow. He breathes still, and his heart beats, because the mind, as you saw in 33 in the chapter on the Muscles, does not control these operations. If the blow break the skull, and the broken part be pressed in upon the brain, the man will not think, and feel, and move, until the surgeon remove the pressure by raising the broken piece. 4. The brain is shown to be the organ of the mind by the manner in which the mind is affected by dis- ease in the brain. Fever causes delirium by disordering the brain, and a violent inflammation of the brain pro- duces fierce delirium. We sometimes see the mind blotted out, step by step, by slow disease in the brain, How do you know that the mind is not in every part ? "What is said of the consciousness that the mind has its seat in the brain? "What fact can you cite that proves that it has its seat there ? 182 FIRST BOOK IN PHYSIOLOGY. so that the strong-minded man becomes gradually like an idiot. 5. You see, then, that the mind or soul, so long as it remains in the body, is dependent upon the brain. It can act only ~by means of this organ. If the brain be disordered in any way, the mind acts in a disordered manner. If the brain be much pressed upon, the mind cannot think, nor feel, nor move any part of the body. The mind is still there, but it is torpid. When the pressure is taken off, it comes out of this torpid state. 6. As the brain is the organ with which the think- ing is done, we find that those animals that think much have larger brains than those that think but lit- tle. A frog thinks very little, and he has a small brain. An oyster thinks still less, and it would be hard to make out where his brain is. But such ani- mals as the canary-bird, the dog, and the horse, that know so much, have brains of considerable size. Man has a larger brain in proportion to his body than any other animal, because he has to think so much more than other animals do. And men that think much have larger brains than the stupid and ignorant. 7. The mind in the infant is feeble, just like its body. It knows but little. But as the body grows, the mind grows also, and continually adds to its know- ledge. I wish to show you now how it does this. 8. If you look at a very young infant, you will see that it does not know as yet how to use its mus- cles at all well. It moves its hands about awkwardly. How does disease sometimes show that the miud resides iu the brain ? What is said of the size of the brain iu different animals and iu man ? What is sai j of the mind of the infant ? CONNECTION OF THE MIND AND BODY. 183 It cannot even hold any thing in them. It does not use its eyes well. It cannot turn them so as to look directly at any thing, but they roll about in their sockets irregularly. It does not see any thing clearly. 9. The mind, you see, then, has to learn to use its instruments, the senses and the muscles. And the more it learns how to use them, the more knowledge it gets of the world around it. It learns, for example, to use the muscles and the nerves of touch, so as to know hard things from soft, rough from smooth, &c. In these ways it is continually learning more and more about the world of things with which it is sur- rounded. 10. In learning to use the senses, the mind makes one sense help another. Thus, the child sees a thing held before it, but as he reaches out his hands to touch it, it is plain that he does not know at first how far off it is. But after a while, by touching it again and again, he knows where it is. That is, by his sense of touch he corrects the report which the sense of sight makes to his mind. He makes many such corrections every day, and after awhile becomes able generally to estimate at what distance objects are the moment he looks at them. Just so the infant has to learn to use its ears as well as its eyes. It knows nothing at first of the direction of sound, or of the distance from which it comes. is said of the use which the infaot makes of the muscles and the senses ? What is said of its learning to use them ? Illustrate the fact that the mind makes one sense help another in learning to use the 184 FIRST BOOK IN PHYSIOLOGY. 11. It is a long training that the mind has to go through in learning to use the muscles. The hand of the infant is of little use at first, but after a time he learns to hold things in it. And from this the mind goes on to use the muscles of the hand more and more, till, in some cases, as in the skilful engraver or penman, it acquires wonderful skill in the movement of these muscles. The child learns to perform many different motions before he comes to try that very general motion of the muscles of the body, creeping. And then, in learning to walk, all the muscles that move the body, the head, the legs and the arms, are exercised in balancing movements, day after day, for a long time, before he can acquire such skill in the use of the muscles as to walk off readily and with scarcely thinking of what he is doing. 12. In learning to talk and sing, the mind learns how to use muscles, just as in learning to walk. These are nicer and more difficult operations, and so it takes the mind longer to learn them than to learn to use the muscles in walking. Especially is this true of learn- ing to sing. The mind is obliged to practice a long time on the muscles of the larynx, in order to use them skilfully in singing. 13. In training the muscles of the voice in speaking and in singing, the ear acts as the teacher. It is only by the hearing that we know that we make the right sounds. When the child begins to talk, he makes various trials of the sounds that he wishes to utter, his What is said of the time required for learning to use the muscles ? What is said of learning to talk and sing ? Why does it take longer to learn to do these than to learn to walk ? CONNECTION OF THE MIND AND BODY. 185 ear all the time listening, that his mind may know when he utters them correctly. So, when one is learn- ing to sing, the ear listens to inform the mind when the note is properly sounded. In learning both to talk and sing, the ear is thus continually correcting the mistakes which the mind makes in using the mus- cles of the voice. 14. So necessary is the ear in the training of the muscles of the voice, that these muscles are never used in a child that is born deaf. In almost all the deaf and dumb there is no defect in the organs of the voice. The apparatus is all there the articulating parts, the tongue, palate, &c., the larynx with its vocal ligaments, and the muscles that tighten them, so that they may vibrate, and the muscles of the chest that force out the air to strike upon them. And the mind has its nerves running from the brain to all parts of the apparatus. But the mind does not work the appara- tus, or play on the instrument, as we may say, simply because it has no guide in doing it. There being no hearing, the mind has no means of knowing when the right sound is uttered, and therefore it utters none. The deaf and dumb are dumb because they are deaf. 15. If a child, instead of being born deaf, becomes deaf while it is learning to talk, he will remember the motions of the muscles of the voice by which he uttered some words, the names of common objects, such as hat, watch, &c. He can therefore pronounce these words, but he does it very awkwardly, because there is no hearing to guide the voice. What acts as the teacher in learning to talk and sing ? Illustrate this. What is said of the deaf and dumb ? What is said of children that become deaf and dumb while learning to talk ? 186 FIRST BOOK IN PHYSIOLOGY. 16. I have thus told you how the mind uses the muscles of the body. It is a very complicated ma- chinery that the mind works. There are over four hundred muscles in the body, and the mind works them by a multitude of nerves that go from the brain to them. 17. Observe, now, that the mind in most cases knows nothing about all this machinery of the mus- cles. Your mind wills that your hand be raised, and it is instantly done. You may not know what muscles do this, and if you do you cannot perform the motion any better than if you did not know. The anatomist that knows the names of all the muscles, and under- stands how they are arranged, cannot use them any better than those who know nothing about this. The skilful balancer would not be any more skilful, if he had all the knowledge which the anatomist has. The famous singer could not sing any better if he should know how the little muscles in his throat work in pro- ducing the different notes. 13. When man works any machinery that he has made, it is necessary that he should understand its various contrivances. Thus, the sailor cannot guide the ship unless he knows all about its rigging. But it is not so, as you have seen, with the machinery that the mind works in the body. The mind does not look at the hundreds of muscles that it works, as the sailor looks at the various ropes with which he man- What is said of the muscular machinery that the mind works ? How much does the mind know about this machinery ? Could it work any better if it knew all about it ? State the comparison given in regard to machinery made by man. CONNECTION OF THE MIND AND BODY. 187 ages his vessel. And when it wishes to perform any motion, it is not obliged to consider what muscles it must put into action. It simply wills that the motion shall be done, and instantly something, we know not what, goes along a multitude of nerves to a multitude of muscular fibres, and they contract just enough to perform the motion. 19. For every different motion a different message, as we may call it, is sent along the nerves. If you raise your hand, a message is sent through the nerves to the muscles that do it. Now, if you raise it again, but in a little different manner, a little lower or higher, or a little more to one or the other side, a lit- tle different message is sent along the nerves to those muscles. And the same can be said of the muscles of any other part of the body. You see, then, that while any machinery made by man can perform but a few motions, this machinery of the muscles can perform motions of any variety. 20. I have already spoken of the variety of mo- tion that the muscular machinery can perform^ in the chapter on the muscles, 12 and 13, and therefore will not dwell on it here. For all this variety there is a corresponding variety in the messages or impres- sions sent from the mind to the muscles. Even when the muscles only vary in the degree of their action, for every different degree there must be a different message. Thus, if in playing on a piano, you press said of the different motions performed by muscles ? Illus- trate by referring to the hand. What is said of the great variety of muscular action. Illustrate this variety as produced by varying the degree and the direction of the action of muscles? 188 FIRST BOOK IN PHYSIOLOGY, on the same key twice in the same way, except that you vary the degree of pressure, two different mes- sages are sent to the muscles that make the pressure, telling them in each case how hard to press. Much more, then, must the messages of the mind to the mus- cles vary, when their action is not only varied in de- gree, but in direction also, as when the hand moves from one key to another in playing on the piano. 21. In the chapter on the Muscles you saw that generally many muscles act together in producing any motion. For the different motions of any part, then, there must be a vast variety of messages sent along the nerves of the muscles in that part. You can get some idea of this variety, if you move your hand about in as many different ways as you can think of, remembering what a number of muscles there is at work while you are doing this. 22. In estimating the variety of the messages sent to the muscles, you are to remember that a separate message is sent to every fibre of a muscle by its little nervous tube, as mentioned in 9, in the chapter on the Nervous System. How wonderful it is, that in all this multitude of messages that are sent to the fibres of the muscles, there should commonly be no mistake in any of them. In every motion each fibre gets its message correctly, and acts in obedience to it. You will realize how wonderful this is, if you turn back to the chapter on the Muscles, and read again What is said in 21 of the variety of messages sent by the nerves to the muscles of any part ? What are you to remember in estimating this variety ? What is very wonderful in regard to this ? CONNECTION OF THE MIND AND BODY. 189 all that I say there of the variety there is in the action of the muscles. 23. When the muscles in different parts of the body are at work at the same time, in some general movement, the variety of messages that go to and from the brain is inconceivably great. "When one is walking, for example, the mind continually sends a multitude of messages to all the muscles that together perform this general motion of the machinery. At the same time there are messages going to the brain from some of the organs of the senses, perhaps from all of them. But the variety in the messages is more strik- ing when different motions are performed in different parts of the body. Observe one who is playing on a parlor organ, and at the same time is singing. Mes- sages are sent in this case to many different parts for different purposes to the muscles of the foot that work the bellows to the muscles of the arm and hand and fingers in playing on the keys to the muscles of the eyes in moving them to look at the notes to the muscles of the vocal ligaments in making the different notes to the muscles of the throat, lips, &c., in arti- culating the sounds and to the muscles of the chest in forcing out the air through the windpipe. While all this is going on, the ear is listening to discover if there be any error in the sounds, the eyes are looking at the notes, and the sense of touch is guiding the muscles of the hand in regulating the degree of press- ure on the keys of the organ. That is, while messages What is said of the variety of messages that go along the nerves when one is walking ? In what cases is this variety most striking ? Give the illustration. 190 FIRST BOOK IN PHYSIOLOGY. are going from the mind with such rapidity and va- riety to the muscles of the foot, the hands, the eyes, the throat and the chest, messages are coming to the mind from the ears, the eyes and the fingers. The communications of the mind with the different parts of the body are in such a case numerous and compli- cated beyond conception. 24. I have thus shown you how the mind makes use of its instruments, the organs of the senses and the muscles. I have spoken of them as the machinery of the mind, and you have seen that these instruments contain mechanisms that are more perfect and beauti- ful than any that man ever constructed. You have seen that the body is mostly a collection of machinery for the mind to use, and that the purpose of those parts which the mind does not use is to build those which it does use. The object of one portion of the machinery of the mind, the organs of the senses, is, as you have seen, to enable it to gain a knowledge of the world around it. The object of the other portion of its machinery, the muscles, with the parts that they move, is to use this knowledge gained by the senses in making impressions upon the things and beings with which it is surrounded. It works with the muscles, and with them communicates its knowledge to others. 25. This machinery of the mind is 'fitted for our present state of being. But this life is short. This body, with all its ingenious and beautiful contrivances, is to be dwelt in and used by the mind but a short period of time. In the life which follows, its ever- Give the summary in 24. "What is said of the instruments which the mind will use in another life ? CONNECTION OF THE MIND AND BODY. 191 lasting life, it is to have, as the Bible tells us, a better, a glorified body. It will, therefore, have better in- struments to use then than it has now, and so will be able both to know more and to do more than it can in its present state. 36096 UNIVERSITY OF CALIFORNIA LIBRARY