10 PHYSIOLOGY Animal In the natural hierarchy of the sciences, physiology fol- aml vital i ows after chemistry, which in turn follows physics, molar spirits. an( j mo i ecu i ar . an d in a natural development, as indeed is evident from what we have just seen, the study of the two latter should precede that of the former. At a very early age, however, the exigencies of life brought the study of man, and so of physiology, to the front before its time ; hence the history of physiology consists to a large extent, especially in its opening chapters, of premature vain attempts to solve physical and chemical problems before the advent of adequate physical or chemical knowledge. But no ignorance of these matters could hide from the observant mind, even in quite early times, two salient points which appear also in the analysis just given, namely, that, while some of the phenomena of living beings seem due to powers wholly unknown in things which are not living, other phenomena, though at first sight special to living beings, appear to be in reality the peculiar outcome of processes taking place as well in things not alive. It was further early seen that, while the former are much more conspicuous, and make up a greater part of the life of the individual in those living beings which are called animals, especially in man, and in animals more closely resembling man, than in those which are called plants, the latter are common to both divisions of living things. Both sets of phenomena, however, were at first regarded as the products of certain special agencies ; both were spoken of as the work of certain spirits ; and the distinction between the two was formulated by speaking of the spirits as being in the former case animal and in the latter vital. From the very outset even the casual observer could not fail to be struck with the fact that many of the pro cesses of living beings appear to be the results of the various contrivances or machines of which a living body is largely built up. This indeed was evident even before the distinction between animal and vital spirits was recog nized ; and, when that differentiation was accepted, it was seen that the part played by these machines and contriv ances in determining the actions of living beings w r as much more conspicuous in the domain of vital than of animal spirits. As inquiry was pushed forward the prominence and importance of this machinery became greater and greater, more especially since the phenomena supposed to be due to the agency of vital spirits proved more open to direct observation and experiment than those attributed to the animal spirits. It was found that the most fruitful path of investigation lay in the direction of studying the structure and independent action of the several constituent machines of the body, and of unravelling their mutual relations. Organs These machines received the names of organs, the work tlfuuc- or action of an organ being at a later period spoken of as its function. And, when it became clear that many of the problems concerned with what was supposed to be the work of the vital spirits could be solved by the proper appreciation of the functions of certain organs, it was in ferred that the more difficult problems belonging to the animal spirits could be solved in the same way. Still later on it was found that the conception of organs and functions was not only quite separable from, but indeed antagonistic to, the hypothesis of the entities called spirits. In this way the first great phase, as it may be called, of the science of physiology was evolved, a phase which lasted till quite recent times. Under this conception every living being, plant or animal, was regarded as a complex of organs, each with its respective function, as an engine built up of a number of intricately contrived machines, each performing its specific work. The whole animal body was parcelled out into organs, each of which was supposed to have its appropriate function ; and the tions. efforts of investigators were directed, on the one hand, to a careful examination of the structural features of an organ with the view of determining by deduction what its function must be, and, on the other hand, to confirming or correcting by observation and experiment the conclusions thus reached by the anatomical method. And the fruit- fulness of this line of inquiry proved so great that the ideas directing it became absolutely dominant. In many cases the problem to be worked out was in reality a purely mechanical one. This was notably so in the great ques tion of the circulation so brilliantly solved by Harvey. Putting aside for a while the inquiry as to the origin of the force with which the walls of the heart press on the blood contained in its cavities, accepting the fact that the blood is thus pressed at each beat of the heart, all the other truths of the circulation which Harvey demonstrated are simply the outcome of certain mechanical conditions, such as the position and arrangement of the valves, the connexion of various patent tubes, and the like. And many other problems as, for instance, those connected with respiration proved to be similarly capable of solution by the application of ordinary mechanical principles to anatomical facts. So fruitful, and consequently so adequate, seemed thi.s conception of living beings as built up of contrivances or organs, in contrast with the lifeless world in whose mono tonous masses no such structural disposition could be recognized, that the word "organic" came into use as a term distinctive of living things. The phrase was especi ally adopted by the chemists, who for a long time classified their material into "organic" substances, i.e., substances found only in living beings, and into inorganic substances, that is, substances occurring in lifeless bodies as well. Indeed, this nomenclature has not even yet been wholly abandoned. Triumphant, however, as was this mode of inquiry in these and similar instances, there remained in every investigation an unsolvable residue, like the question of the origin of the force exerted by the heart referred to above in speaking of Harvey s work ; and in many other instances the questions which could not be solved on mechanical principles formed a great part of the whole problem. Thus in the case of the liver careful dissection showed that minute tubes starting from all parts of the liver joined into one large canal, which opened into the small intestine, and observation and experiment taught that these tubes during life conveyed from the liver to the intestine a peculiar fluid called bile, which appeared on the one hand to originate in the liver, and on the other to be used up for some purposes in the intestine. But here the mere mechanical flow of the bile along the gall- ducts, instead of being of primary, was merely of second ary importance, and the problem of how the bile was generated and made its way into the small beginnings of the ducts was the greater part of the whole matter. Thi.s latter problem was left unsolved, and indeed for a while unattempted. Nevertheless the success in other directions attending the conception of organs and functions encour aged physiologists to speak of the liver as an organ whose function was to secrete bile, and further, led them to ignore to a large extent the great unsolved portion of the problem, and to regard the mere enunciation of the function as the chief end of physiological inquiry. Moreover, whenever attempts were made to unravel these obscurer problems, the efforts of investigators were mainly confined to a fuller and more complete elucidation of the supposed function of an organ, and the method of inquiry adopted was in most cases one which regarded the finer elements of the part studied as minute organs making up the whole gross organ, and which sought to explain the
functions of these smaller organs on the same mechanical