IIHDIA_N PHYSIOLOGY. _
AMONG the many eminent men in every department of physical science, of whom America is justly proud, no name stands higher than that of Professor Draper. His elaborate and philosophical work on " The Forces' concerned in the Organization of Plants," and his other researches into the mutual relations of light and the forces of chemistry and life, have long established his claim to be heard as an authority upon all subjects connected with the intri- cate dynamical theories of physiology and physics. Most wel- come, therefore, to all lovers of science was the announcement of a systematic work on physiology from his pen ; which might be expected to contain a complete exhibition of the results obtained by his various investigations into the problems of vitality and organization. And the expectations which Professor Draper'spre- vious reputation had raised are justified by the contents of his volume. It is based upon the lectures delivered to his class in the Medical School of New York, and is accordingly elementary and simple in its style. It is free from minute records of experi- ments and the details of special investigations, but the general re- sults of much labour in the laboratory and dissecting-room, and pro- found meditation on the materials thus acquired, are summed up in precise and lucid language, and presented in a style at once simple and picturesque. The bulk of the volume is necessarily occupied with the exposition of established facts ; its chief novelty is in the view that is presented of the connexion between life and the other phenomena of nature, and its relation to the forces which constitute the domain of physics. To put this subject fairly before the reader, we will endeavour to indicate very briefly the general characteristics of two opposing views, which are, or may be, held respecting organic life, and we will then let Professor Draper expound his own position. The view which answers best to our natural impressions, and is first suggested by a cursory inspection of the facts, is that which re- gards organic life as a distinct power in nature, and postulates the Vital Force as an ultimate and irresolvable entity. The or- ganic world seems to be embosomed in the inorganic as a thing apart, and disowning all identity. As if dead matter had been first prepared as a receptacle, and then life was added as a fact in nature wholly new. This is the natural, and hitherto most pre- valent doctrine : opposed to it stands another, not wholly confined to modern times indeed, yet in its scientific form entirely of recent origin. According to this view, what we call life is not a distinct essence or power, but is an exemplification and carrying out, under special conditions, of the same laws which regulate all na- ture. The organic and inorganic processes differ not in essence, but inform. The living germs supply not an agent by which certain effects are produced, but a condition only, under which the forces, light, or heat, or chemical action, or any others, are brought into peculiar modes of action. If, in some respects, the difference between these two views may seem to be slight, in respect to the deepest questions it is profound and paramount. If physical life be an essence sui generic, then the field of physiological inquiry is confined within narrow bounds. The " Vital -Force " gives a ready answer to every ques- tion respecting causes, and investigation is limited to matters of detail. But on the other view, the attitude of science towards vital phenomena is entirely different. If the problem be to trace in these the operation of intelligible and universal laws ; to de- tect simplicity in mysterious facts ; and discover how, by variety • Human Physiology, ,&tatical and Dynamical ; or, the Conditions and Course of the Life of Man. By Jahn William Draper, M.D., LL.D., Professor of Che- mistry and Physiology in the University of New York. Published by Sampson Low, Son, and Co.
of eircunistance and condition, unvarying principles may issue in results, discordant, or apparently opposed ; then is the scope of physiological inquiry freed from all special limitations. Thus speaks Dr. Draper :—
" The problems of organization are not to be solved by empirical schemes; they require the patient application of all the aids that can be furnished by all other branches of human knowledge, and even then the solution comes tardily. Yet there is no cause for us to adopt thee° quick but visionary speculations, or to despair of giving the true explanation of all physio- logical facts. Since it is given us to know our own existence, and be con- scious of our own individuality, we may rest assured that we have what is in reality a far less wonderful power, the capacity of comprehending all the conditions of our life. God has framed our understanding to grasp all these things. For my own part, I have no sympathy with those who say of this or that physiological problem, it is above our reason. My faith in the power of the intellect of man is profound. Far from supposing that there are many things in the structure and functions of the body which we can never comprehend, I believe there is nothing in it that we shall not at last explain. Then, and not till then, will man be a perfect monument of the wisdom and power of his Maker, a created being knowing his own existence, and capable of explaining it." But while the decided preference may be given on general grounds to a scientific view of vital phenomena which regards them as wholly conformed to law, and lit subjects for investiga- tion, it is necessary not to close our eyes to the difficulty of the task, or to the arguments which favour the opposite opinion. These have been strongly urged by Professor Agassiz in his recent work on Classification, and in truth they are very obvious. No known operation of the forces at work in organic nature is capable of producing organic phenomena. It has, hitherto, been only by analogy, and by general considerations, that the doctrine of the identity between the laws of these two domains of nature has been supported. The actual link which unites them has not been ca- pable of demonstration. A beautiful application of the analogi- cal argument is furnished by Professor Draper in reference to the phenomena of Allotropism, showing how a similar law may be oonoeived as regulating various organic processes. But it is to be remembered that this is analogy only ; it is possibly or probably true ; is rightly in the absence of other evidence to be supposed ; it has not been aotually proved.
" All elementary substances appear to have the quality ef assuming active and passive oonditious. Carbon, moreover, presents many intermediate forms. As diamond it is extremely incombustible, and is set on fire with difficulty even in oxygen gat ; as lampblack it will kindle spontaneously. With these differences in its relations with oxygen, it also exhibits great variations in its optical, calorific, mechanical, and other properties. These transitions of state may be induced by various causes, especially by the agency of what arc called the imponderable principles, as by rise of tempe- rature, and exposure to the sunlight. Thus, in the case of chlorine, I.have shown that, though it refuses to combine with hydrogen so long as it is in the dark, an exposure to indigo-coloured light will cause it to unite with explosive energy with that substance ; and these peculiarities are retained by bodies when they go into union with each other. Thus there are two forms of phosphorus, the one active and shining in the dark, and therefore readily oxidizable ; the other passive, not shining in the dark, and with therefore a less affinity for oxygen ; and these severally give rise to two va- rieties of phoaphureted hydrogen, which, though having the same compo- sition, yet differ in this respect, that the one containing the active form of phosphorus is spontaneously combustible in the air, but the other, which contains the passive form, is not spontaneously combustible. Phosphorus is thrown from the active to the inactive state by mere exposure to the more refrangible rays of the sun. " The properties here spoken of have been designated by Berzelius as the allotropism of bodies. I have endeavoured to prove that allotropism is the true_cause of many of the obscure facts which we meet with in the animal mechanism ; for it is very clear that something so modifies the relations of the tissues to oxygen that they are not indiscriminately destroyed by it, but these parts yield in a measured or regulated way ; and since, in inorganic substances, the influeuce of the impouderables can compel the assumption of an active or passive state, there is nothing contradictory in imputing to the nervous system a similar power. "In this manner we may therefore conclude, that so far as tissue de- struction is concerned, the nervous system possesses a governing or con- trolling power ; that by keeping parts in states answering to the passive and active conditions of inorganic chemistry, it can suspend the action of the respired oxygen or permit it to take effect."
According to Dr. Draper the forces on which growth depends. are furnished wholly from without, and are especially due to the influence of light. Thus the sun is the chief or only source of vital action. But there resides in every germ a plastic power by which these forces are directed into certain modes of operation. The living organism has a directive or determining function ; it causes the external force to produce specific organic compounds, and to build them up into determinate forms. In the nature of this power lies the whole question in dispute. Is it a special agent, or is it a condition only ? To elucidate this-Abject Dr. Draper refers to the analogy of the flame of a lamp,evhich has a definite form, and propagates its like ; yet is nothing. but an ope- ration continually maintained or extending, so long as the con- ditions are similar.
"Are plants, then," he asks, "in truth, nothing more than temporary states through which material substance is passing, because of some original physical impression made upon it, and the present operation of external cir- cumstances ? Can individuality be applied to them any more than to a flame ? Instead of being individuals, are they not rather the transitory results of an operation ? "The lamp, which we have been using as an illustration, may serve to enlighten our path a little farther. In the infancy of chemistry, it might have been said of it that it possessed a burning power, which enabled it to dispose of the matter with which it was fed,just as we say of a plant, in the infancy of physiology, that it possesses a plastic power, which groups into definite forms the substance with which it is furnished. The so-called burn- ing power was derived from another flame, in all respects analogous to that which manifests it, and is nothing more than an extension of a physical operation, the tendency of which, so far from being to check, is to continue as long as the proper material is furnished. The lighting of a second flame ie essentially the same condition as the continued combustion in the first. The fact of separateness changes the phenomenon in no respect whatever ; the relation of two separate flames is the same as that of two different parts of the same flame ; and so the derivation of a plastic power by a plant from its ancestor is essentially the same thing as the manifestation of a similar
power in different parte ef its own system. •
" Though it may therefore be convenient to speak hypothetically of this principle which accomplishes in a plant the grouping of its parts as if it were an agent, the foregoing illustrations show ns that all the facts of the case are equally well satisfied on the supposition that it is the continuation of an operation. A multitude of parallel instances present themselves. In the making of leavened bread, all the phenomena would seem to be accounted for either upon the hypothesis that there resides in the leaven or ferment an agent, whose quality it is to determine a specific change in the flour, or that there is an operation which, because of the chemical conditions existing, is gradually spreading, and which will not cease until all the material sub- mitted to it has been affected, and this no matter whether it be in the same mass or in successive portions. Of such hypotheses, the first is merely an elementary idea, the latter involves a philosophical conception.
" In this way, therefore, the so-called plastic power of a cell or the germ of a seed may be regarded as the continued manifestation of an antecedent impression long ago made, and which, under the existing conditions, has no liability to wear out or die away ; and that impression may have been purely physical in its nature."
We recognize in this representation evidence of a truly philo- sophic mind, and a most admirable exhibition of the light in which the problem presented by organic nature should be re- garded. But can we take yet another step, and presenting the problem in a more definite form, attain an answer more precise ? Can we demonstrate what the nature of that condition must be— of what kind that operation—by which the organic state is educed from the absorption of light ? We think this is possible. There is one analogy which is very simple, and very obvious when it is pointed out, but which even Dr. Draper seems to have partly over- looked. It is the analogy between the animal body and a ma- chine, as a watch or a steam-engine. These two classes of bodies possess in common an active power, apparently spontaneous ; that is, truly, dependent on the operation of force contained within themselves. What is the nature of this force in the case of a maohine ? Evidently it is the existence within it of tension, or of matter in a state of tension ; that is, of matter whioh has a tendency to change its state. But the matter of which the animal body consists tends to change its state. It decomposes " spontaneously " under ordinary circumstances; as the spring of a watch spontaneously unbends, or compressed steam spon- taneously expands. In the decomposition of organized substance, force is generated—heat, e. g., is habitually recognized—why not also motion ? or nervous action ? Why are not these functions the result of the regulated decomposition of the tissues as simply and intelligibly as the motions of a watch are the result of the un- bending of the spring. Is not the power of animal bodies as much an instance of known and necessary laws, as simple an exhibition of the nature and universal characteristics of force, as any moat ordinary fact can be ? The living tissues are substances in which force exists as tension, and in the animal body they are so placed as to effect certain ends through that tension ; that is in the act of losing it, just as when a bent spring is placed within a watch. Adopting this view, which seems to be merely giving the plain and evident the preference over the vague and hypothetical, the active powers of organic life cease to be distinguished from other forms of the active powers of Nature. And a light is diffused, also, upon the nature of that " operation " by which organic life is maintained and spread. Nutrition is the production of a tension. The luminous rays to which Dr. Draper refers all organization are expended in bringing into a state of tension the matter which is rendered organic by their agency. Living tissues
are representatives of a certain mode of tension among the par- ticles of matter. By force, the elements of carbonic acid, or ammonia, &c., are as it were wrenched apart, and force is stored up in them, as it is in the drawn string of a bow, or a lifted weight. The farther discussion of this subject we cannot now attempt, nor have we space for any remarks on the nature of Organic Forms and the conditions by which they are regulated. Very briefly we must advert to the views advocated by Dr. Draper respecting some special physiological questions ; such as his argu- ment (p. 147) respecting the circulation, in which he most ingeniously supports the view that it is effected chiefly by means of the chemical reactions between the blood and the tissues, and that the heart represents the special localization of a function which exists independently and in every part. The introduction of arguments in proof of the immortality of the soul, the advantages of the Sabbath, and other doctrines of natural and revealed religion, in a scientific treatise designed for professional students, is perhaps characteristic of its American origin, but we think they will be welcome also to most English readers. The arguments possess somewhat of novelty, at least in form. The following is Dr. Draper's justification of his course.
"Believing that the right progress of society depends on its religious opinions, and observing with concern the growing carelessness which is manifested in these respects in our times, the author has not hesitated to show hew advantage may be taken of the facts presented by physiology. . . . . It would be in vain to discourage the cultivators of Positive Science from attempting the solution of questions which have foiled Speculative Philosophy. The attempt will certainly be made, and will inevitably con- duct us to the truth. Our concern should be to direct it from the outset in the right course. "The existence of God, his goodness, power, and other attributes; the existence of the soul of man, its immortality and accountability ; the future life ; our relations to and position in the world ; its government ; these are topics with which Physical Science is concerning itself, and from which Physiology can not hereafter be disconnected."
Of the soundness of his arguments different opinions will probably
be entertained, but all must recognize in them tokens of a heart in which scientific research has added to the keenness of the spiritual sensibility, and rendered more profound and manly a sympathy with all that is highest and purest in our common humanity.
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