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O WHAT END? 
 
 EMARKS MADE AT THE CLOSE OF THE 
 THOMSON LECTURES FOR 1894-95, IN 
 THE FREE CHURCH COLLEGE, 
 ABERDEEN, ON 
 
 THE PHENOMENA OF LIFE. 
 
 BY 
 
 JOHN GRAY M^KENDRICK, 
 
 > * f 
 
 PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF GLASGOW. 
 
 [jpvintcb for ^ribatr Cirtnlation.] ' 
 
 GLASGOW: 
 
 JAMES MACLEHOSE & SONS, 
 
 PUBLISHERS TO THE UNIVERSITY. 
 
 1895. 
 
 I 
 
Digitized by the Internet Archive 
 in 2016 
 
 https://archive.org/details/towhatendremarksOOmken 
 
S ?. O Florence Blackburn 
 
 I 04 
 
 Vy ^ 
 
 TO WHAT END ? 
 
 In drawing this course of lectures to a dose, we 
 may ask ourselves the question — What general notions 
 regarding the nature of living action may be formed 
 from a careful consideration of the facts marshalled 
 along the four lines of evidence brought under review, 
 namely, the histological, chemical, physical, and experi- 
 mental ? My object has been to illustrate the progress 
 of physiology along these four lines of research, so as, if 
 possible, to give you a view of the aims and problems, 
 the difficulties and the successes, of physiological science. 
 
 In the first place, we have seen that the microscope 
 of the present day, which bears the same relation to the 
 microscope of fifty years ago as a modern astronomical 
 telescope does to that used by Galileo, aided by special 
 methods of preparing the tissues for examination, has 
 revealed deta ils of structure in certain kinds of living 
 matter that have hitherto been regarded as structureless, 
 and, in particular, has shown remarkable phenomena in 
 the nuclei of cells during the reproductive process. Par- 
 ticles of living matter, the diameters of which are 
 expressed in thousandths of an inch, are the arena of 
 movements of a definite character, and apparently for 
 a definite purpose ; and there is a strong probability, to 
 say the least of it, that these movements afford a physical 
 
 \> 40895 
 
4 
 
 basis on which may be constructed a theory of hereditary 
 transmission. At the same time, we must admit that 
 the physical possibilities of the microscope, as an instru- 
 ment of research, have nearly reached their limits, and 
 that we have no right to assume that there may not be 
 movements in living matter which will never be revealed 
 by the microscope ; or, to put the statement in the positive 
 form, it is highly probable that the smallest bit of 
 living matter we can see with the highest powers con- 
 tains still smaller physiological units. Such units may 
 never be seen, but we are at liberty to postulate their 
 existence when we attempt to explain some of the 
 phenomena of life. , 
 
 We then found that the chemical investigation of the 
 phenomena of life is attended with peculiar difficulties. 
 The analysis of living matter is impossible, because 
 analysis destroys the condition we wish to investigate, 
 and, consequently, our knowledge of the chemical pheno- 
 mena in living matter must depend on our knowledge 
 of the chemical constitution of matter that has once 
 lived, and on the chemical behaviour of living matter in 
 certain special conditions. Still we learned enough to 
 satisfy ourselves that the phenomena of vitality are 
 always associated with chemical phenomena, such as the 
 absorption of oxygen and the giving off of carbonic acid 
 and other waste products. Again, however, we found 
 that when living matter is the seat of chemical exchanges 
 the phenomena are always of a molecular character, and 
 occur in conditions that cannot be imitated by the chemist 
 in his laboratory, showing that the vital condition is sni 
 generis. 
 
 We have also sketched the influence of physical 
 methods of research, showing how it is possible to obtain 
 
5 
 
 information as to vital phenomena that would escape 
 observation by the unaided senses. These methods bring 
 to light the fact that phenomena are not always what 
 they seem to be, and that many changes, fundamental in 
 their character, may escape our unaided senses. Such 
 phenomena are illustrated by the latent period of muscular 
 contraction, the rate of transmission of the nervous im- 
 pulse, and the facts of animal electricity. Physiology has 
 gained much, and will gain much more, by the rigorous 
 application of physical methods, but the results obtained 
 have hitherto failed to explain the essential phenomena of 
 living matter, and have only made them more difficult of 
 comprehension. The problem of the essential phenomena 
 of a muscular contraction, or of the transmission of the 
 nervous impulse, has not been much advanced by the 
 knowledge we possess of a muscle curve, and of the rate 
 at which a nervous impulse is transmitted. Still less do 
 we understand in what way electrical phenomena are 
 always associated with vital activity. 
 
 Lastly, we shortly referred to the experimental method 
 by which physiologists are at present engaged in unravel- 
 ling the intricacies of the central nervous system, and we 
 saw that a simpler plan of the nervous mechanism is 
 being slowly worked out. Complicated as the central 
 nervous axis, brain and cord, may at present seem to be, 
 there are indications that its arrangements are in reality 
 constructed on a simple plan, by which segment is bound 
 to segment, and each to all the rest. Still this method 
 throws no light on the real nature of nervous action, and 
 does not presume to discuss that question of questions, 
 the relation of nervous activity to consciousness. 
 
 Probably one of the impressions made on your 
 minds, as you listened to those lectures, is that 
 
6 
 
 physiological science abounds in striking examples of 
 exquisite adjustments and arrangements for the attain- 
 ment of certain ends. It is a truism to state that 
 organs and tissues are adapted, by their structure and 
 chemical constitution, for the performance of specific 
 functions, and yet it is a truism that must ever be kept 
 in mind. Each living unit, such as a cell or the 
 structures formed from cells, is, like a living being in the 
 animal or vegetable kingdoms, adapted to its environ- 
 ment, by which I mean the normal conditions of its 
 existence. Modifications of these conditions affect the 
 functional activity of the organ or tissue, and if the 
 organ or tissue is submitted for a sufficient length of 
 time to new conditions, its texture and histological struc- 
 ture are more or less slowly altered. Thus it is that in 
 the study of the development of organs and tissues we 
 are brought face to face with the same problem as meets 
 the naturalist in his attempts to explain the origin of 
 the innumerable plants and animals that form the sub- 
 jects of his study. How have tissues originated ? How 
 have organs originated ? How have certain mechanisms 
 been formed so as to be adapted to the wants of the 
 higher grades of animals ? Take the simplest tissues as 
 you find these in the body of man. In the animals 
 immediately below him in the scale of existence, you find 
 such tissues similar but not identical, and, as you pass 
 down the scale, you find the points of similarity in 
 structure gradually disappearing until you come to tis- 
 sues in the lower forms that are unlike those in the 
 higher, although they fulfil the same general functions. 
 Trace in this way the connective and muscular tissues 
 up through the animal kingdom and you find a gradual 
 advance, so that the connective tissue and muscle of a 
 
7 
 
 higher mammal are more highly differentiated structures 
 than those, say, of an amphibian or a fish. There has 
 been an advance along the whole line. Every tissue 
 and organ have shared in this progress. The body of one 
 of the higher animals, say that of man, is not therefore 
 an advance only as regards brain and nervous system, 
 as many suppose, but it is a more complicated machine 
 in every detail of its structure. I do not deny that 
 some of the higher mammals have certain tissues and 
 organs more highly developed than we find them in 
 man (as, for example, the olfactory organ in many . 
 animals), but I assert that my statement is gener- 
 ally true. This general advance must be to meet the 
 higher requirements of the higher organisms. What is 
 it that determines these higher requirements ? Evidently 
 it is the evolution of higher and higher psychical pro- 
 perties. For a living being to have sensations, percep- 
 tions, emotions, volitions, and powers of reason more 
 developed than one lower in the scale, it is necessary to 
 have a more differentiated nervous system, and the degree 
 of development of this part of the body determines the 
 degree of development of all the rest. Or, you may state 
 the case in another way : the highly differentiated nervous 
 tissues of man require for their complete development 
 a correlative advance in all the other tissues. Thus 
 epithelium (especially in the sense organs), nerve fibres, 
 nerve cells, muscular tissue, and even connective tissues 
 in man and the higher mammals are all of a higher order 
 than in many of the lower animals because they have 
 all to do with the upbuilding and the upkeep of a more 
 differentiated brain, associated with which we find higher 
 psychical characters. 
 
 Organization therefore is working up to an adequate 
 
8 
 
 manifestation of mind. Mind is the final outcome of 
 those differentiations that have gone on through countless 
 ages in the upbuilding of the kingdoms of living nature, 
 and also in the upbuilding of the highest representative 
 of the highest kingdom, man. Thus we see how the 
 textures and organs of the body are in a sense sub- 
 servient to the manifestation of mind ; and can we doubt 
 that the wonderful progression, the orderly sequence of 
 events in the life history of countless animals, the elabo- 
 ration of more and more complicated tissues in the higher 
 animals until we reach man, processes that have had for 
 their outcome the appearance of mind, must have been 
 directed by Mind itself ? To me any other hypothesis is 
 ' inconceivable. Observe, it is not progression alone that 
 calls for our attention. It is not merely orderly pro- 
 gression. It is progression along a certain definite line 
 that culminates in the manifestation of mind, and the 
 more we scrutinize physiological phenomena of all kinds, 
 the more it becomes evident that they are subservient 
 to this main end. This can only be accounted for by 
 recognizing thought as underlying, controlling, directing 
 ^all living phenomena, and thought, I need hardly say, 
 presupposes a Thinker. Any purely physical explanation 
 of thought is to my mind unreasonable, and if, as I have 
 indicated, thought underlies all physical and vital pheno- 
 mena, and so controls these as to secure as an ultimate 
 phenomenon the manifestation of itself, then I have no 
 difficulty, from the point of view of science, in believing 
 in the existence of a Great Being who is the Source of 
 Energy of this Universe and of all Living Things. This 
 argument advanced from the physiological side has numer- 
 ous applications. 
 
 Let us come back to the question : How far can we 
 
9 
 
 account for the phenomena of life ? Have we yet reached 
 that stage in the history of physiological science at which 
 its conclusions may be accepted, and when we may safely 
 apply them to the consideration of certain great questions 
 that form the subject of study in a theological college ? 
 This is probably the aspect of the matter that fascinates 
 the attention of theological students. It cannot be expected 
 that you will be profoundly interested in the relation of 
 physiological science to the technical art of medicine, nor 
 even to the position of physiology among the sciences, and 
 I will also acquit you of the utilitarian view that physi- 
 ology is only a science that teaches a man what to eat and 
 to drink, and how to live in a state of health and vigour. 
 You wish to know what are its first conclusions. What 
 has it to say regarding those problems that have a bearing 
 on the problems of man’s being and destiny ? How does 
 it deal with those questions in philosophy that form the 
 foundations of ethics and theology? In particular, what 
 has it to say regarding the nature of life ? 
 
 In the first place, a historical consideration of the 
 subject shows us that opinions regarding the nature of 
 life have passed through various phases, and that these 
 phases have been largely influenced by great discov- 
 eries or by the rise of wide-sweeping generalizations 
 in the allied sciences. Thus, at one time, and at a time 
 corresponding with the development of accurate ideas re- 
 garding mechanics and the interplay of mechanical forces, 
 a mechanical explanation was offered of many vital phe- 
 nomena. For example, it was thought that the phenomena 
 of the circulation might be completely explained by the 
 principles of hydraulics, and muscular motion, in the 
 hands of such a philosopher as Borelli, was resolved into 
 a series of problems and theorems based on purely me- 
 
10 
 
 chanical considerations. Again, when the more intimate 
 interchanges of matter that form the subject of chemical 
 research were studied with diligence and success, a school 
 of chemical physiologists arose who thought of life as a 
 series of fermentations, oxidations, reductions, and such 
 like phenomena. To Paracelsus, the first of the chemical 
 physiologists, the emblem of life was a flame, a torch, a 
 combustion, a something in its essence entirely chemical. 
 These mechanical and chemical schools were always in 
 sharp conflict with the vitalists, with such men as Stahl 
 and Whytt and Boerhaave who upheld the view that the 
 essence of life is something immaterial, and that a spirit, 
 an archeus, a vital energy, pervades all living matter, en- 
 dowing it with its properties, and controlling all the 
 physical and chemical operations of which that matter 
 might be the seat. Again, when electrical science took 
 its start, not much more than one hundred years ago, in 
 the physiological experiments of Galvani, electricity became 
 a word that, for a time, was almost synonymous with 
 life, and men thought that '' whatever stirs this mortal 
 frame,’’ especially in nervous actions, was but a mani- 
 festation of this all-pervading force. 
 
 In our own century we have had a striking example 
 of the oscillation of opinion. During the first two or 
 three decades, physiologists were mainly vitalists, although 
 no doubt here and there men were engaged in experi- 
 mental investigations who were guided by mechanical and 
 chemical conceptions. With the rise of the great generaliz- 
 ation of the conservation of energy a new impetus was 
 given to physiological science. If the forces of nature 
 were so related that at no moment could a new force be 
 created or destroyed; if, as was theoretically calculated 
 by Mayer and experimentally demonstrated by Joule, there 
 
11 
 
 was a quantitative relation between any two forces, such 
 as motion and heat ; but if no such quantitative relation 
 could be established between the ordinary forces of matter 
 and vital action (especially that form of vital activity 
 'we call consciousness), thinkers asked the question : Is 
 there a force in living matter distinct from all the 
 other forces, or, in other words, is there such a 
 thing as vitality or a vital force ? Many gave a nega- 
 tive answer. The pendulum swung violently in this 
 direction, and materialistic explanations were everywhere 
 in the air. The brilliant researches of such men as Von 
 Helmholtz, Du Bois Eeymond, Ludwig, and Bonders, each 
 of whom became the centre of a school of eager disciples, 
 advanced to a wonderful extent our knowledge of physio- 
 logical processes. The principle of the conservation of 
 energy became the guiding idea, and many hoped that 
 all the phenomena of living matter would be brought 
 under its domain. For a time the conception of a vital 
 force was scouted, and a physiologist, such as John Good- 
 sir, whose philosophic mind never was satisfied with a 
 purely materialistic explanation, was regarded as old- 
 fashioned. There can be no doubt that the rise of the 
 physico-chemical school was an immense gain to science. 
 
 It stimulated research in all directions, and, in thirty 
 years, greater advances were made in the knowledge of 
 living matter than in the preceding four or five centuries. 
 Then again came a time of reflection, and, as was in- 
 evitable, profound questions were asked as to the nature \ 
 of life and consciousness. Thinkers soon came back to 
 the old problems that often before had baffled the 
 strongest intellects. The psychologists pressed the physio- \ 
 logists for an answer, but no answer came. Some of the 
 greatest physiological thinkers, such men as Von Helm- 
 
12 
 
 holtz, Ludwig, and Bernard, said nothing. Even Von 
 Helmholtz, while he laboured so abundantly in the field 
 between physiology and psychology, has written almost 
 I nothing that expresses an opinion on the fundamental 
 question of the nature of consciousness. Du Bois Rey- 
 rnond, while avowing himself a materialist, still takes 
 refuge in the word '' Ignorabimus,'' and abandons as hope- 
 less the attempt to give a final answer. On the other 
 hand, it must be noted that the very triumphs of phy- 
 siological research, — triumphs won under the guiding 
 influence of a materialistic hypothesis, — have led physio- 
 logists, during the last ten or twenty years, to take up 
 a position, if not less materialistic, at all events implying 
 more caution and judicious restraint. It has been found 
 that, in every case, a purely mechanical explanation of a 
 vital phenomenon is not a complete explanation of the 
 facts. At one time certain vital phenomena were appar- 
 ently easily accounted for by the application of the laws 
 of physical and chemical action. Thus the absorption of 
 food stuffs from the alimentary canal took place in con- 
 formity with the laws that regulated osmotic action, the 
 interchanges of gases in the lungs were supposed to be due 
 to the varying pressures and tensions of the gases on 
 each side of an animal membrane, and the effusion of 
 lymph from the blood into the tissues was looked upon as 
 a mechanical filtration. It is worthy of notice that a 
 more careful examination has shown that in each of these 
 instances the phenomena cannot as yet be entirely accounted 
 for on purely physical principles. In each case a selective 
 action takes place, certain matters may be passed on 
 unchanged, but the rule is that the materials involved in 
 the process are chosen and modified, and that there is a 
 discrimination wholly unaccounted for on the supposition 
 
13 
 
 that the phenomenon is of a purely physical nature. In 
 no instance are the phenomena the same as those which 
 take place when a dead membrane is used instead of a 
 living one. The living membrane, clothed on each side 
 with living cells, modifies and alters the physical process, 
 and gives special characters to the phenomenon in question. 
 The physiologist, therefore, however desirous he may be 
 to explain these phenomena by the application of physical 
 principles, however firmly he may believe that in their 
 essence the phenomena are physical, is bound to admit 
 that the peculiar condition of matter which we call vital 
 not only influences and modifies the physical or chemical 
 process, but gives it special characteristics. Life, vitality, 
 the vital condition, the vital force, call it by what name 
 you please, is still the unknown factor, and the further 
 we press on the more mysterious it seems. 
 
 Step by step, therefore, the physiologist has been driven 
 to study, not so much the mechanisms we find in the 
 body, such as those of digestion, respiration, circulation, 
 etc., but living matter itself. He is back again to ^oto- 
 plasm, or living stuffi He finds, as I have pointed out 
 in these lectures, that it is not structureless, but that in 
 it there are indications of structure minute and delicate 
 almost beyond conception ; he finds also that this living 
 stuff shows much the same properties throughout the 
 whole range of animated existence — it breathes, and 
 moves, and assimilates, and possibly feels — and he finds 
 that the phenomena manifested by this living stuff are 
 fundamentally the same in kind. Thus the phenomena 
 in a secreting cell, in the contractile substance of a 
 muscular fibre, in the tissue of an electric organ, in a 
 nerve cell of the brain or cord, or in the rods and 
 cones of the retina, are all similar in kind, although 
 
14 
 
 varying in degree, and according to the organ in which 
 the structure is found. He is therefore obliged to think 
 of vital phenomena as in their essence molecular : that 
 is to say, that they are due to the interplay, not of 
 large masses of matter, but of molecules, possibly the 
 same molecules as those of the physicist. From this 
 point of view, in the field of what may be called mole- 
 cular physiology, the phenomena demand for their ex- 
 planation the existence of molecules and the interplay of 
 molecular forces just as much as the physical phenomena 
 of heat or light or electricity demand for a rational 
 explanation material particles and the interplay of forces 
 in a hypothetical ether or medium in which they are 
 embedded. Thus the phenomena of life, according to 
 my conception, may be as intimately connected with 
 the primary properties of matter, and possibly with the 
 ether that now plays so large a part in the speculations 
 of physicists, as those of gravitation, or light, or elec- 
 tricity, or elasticity. We now see how far off we are 
 from any adequate explanation of vitality. If it is a 
 physical force it is one the nature of which we have 
 hardly begun to understand. To refer it to the interplay 
 of the physical forces already so far krmwn is an in- 
 sufficient explanation. A study of what we mean by life 
 soon brings us face to face with profound questions as to 
 the real nature of matter and energy that lie at the basis 
 of all science and philosophy. 
 
 The thoughtful physiologist runs no risk therefore of 
 becoming a materialist in the grosser sense of the term. 
 The study of his science amplifies and enlarges his views 
 of matter, but when his analysis is pushed to its extreme 
 limits, he is brought face to face with another order of 
 facts and another order of phenomena. To these give 
 
15 
 
 the name of spiritual, although we cannot define what we 
 mean by this word any more than we can define what 
 we mean by matter or energy. Here the physiologist 
 must stop, and indeed I may say most physiologists stop 
 long before they reach such speculations in the depart- 
 ment Herbert Spencer has termed transcendental physiology. 
 
 We now pass into another region of thought, that of 
 metaphysics and theology. With this region I have, in 
 such a course of lectures as this, nothing to do. My 
 duty has been fulfilled when I have brought you to the 
 borderland, and when possibly I have led you to the 
 conviction that there is nothing in physiological science 
 which negatives the existence of something beyond its 
 territory. It is, in my judgment, only a superficial view 
 of science that leads any one to assert, as Haeckel does 
 in his last little book on ''Monism,’’ that all the phe- 
 nomena of the universe — mental as well as physical — 
 can be explained as conditions of matter and energy. 
 That may be the outcome in the far-off future, but 
 we may safely assert that our present knowledge does 
 not warrant such a statement, unless you give to the 
 term energy a much under meaning than is usually 
 applied to it hy physicists. Whilst, therefore, the attitude 
 of every thinker towards these questions should be one 
 of cautious reserve, and whilst we rest confident in the 
 belief that no speculations on life and death and immor- 
 tality and God that crush the highest aspirations of 
 the human soul can be truly philosophical, we should 
 beware of hampering the progress of scientific research. 
 Science must be true to her methods and to her canons 
 of criticism. She must work on irrespective of con- 
 sequences. She must have freedom ; and even when 
 
 we bring her conclusions to the bar and find that they 
 
cannot be justified if they seem to be in conflict with 
 other philosophical conceptions that rest on a sure 
 foundation, such as those of God and Duty and Ee- 
 sponsibility, we must not check her course. Theologians 
 need not be afraid of science. They may rest assured 
 that science is a revelation of God, and that sometime 
 or other, the views of theologians, which, in their turn, 
 can only be partial and not final, and the views of men 
 of science who deal with the physical universe, will 
 meet at a common point. A monistic theory of the uni- 
 verse will by and by be possible, but not now. What 
 we have to dread are premature generalizations, either 
 on the one side or the other ; attempts to establish 
 harmonies where evidently no adjustment is at present 
 possible, and declarations to the unlearned multitude of 
 antagonisms that do not really exist. My last word to 
 you, students of Theology, is the expression of my firm 
 conviction that there is nothing in the doctrines of 
 physiological science inconsistent with the teachings of 
 the Great Founder of Christianity, who, when He dis- 
 cussed some of the mysteries of human existence, 
 brought men back to God by the lessons of the lily of 
 the field and the fowls of the air. 
 
 GI.ASGOW : PRINTED AT THE UNIVERSITY PRESS BY ROBERT MACLEHOSE AND CO.