472 



NA TURE 



[September 14, 1893 



biology from the exact sciences, and that in the vast field of 

 biological inquiry the end we have is not merely, as in natural 

 philosophy, to investigate the relation between the phenomenon 

 and the antecedent and concomitant conditions on which it 

 depends, but to possess this knowledge in constant reference to 

 the interest of the organism. It may perhaps be thought that 

 this way of putting it is too teleological, and that in taking.as it 

 were, as my text this evening so old-fashioned a biologist as 

 Treviranus, I am yielding to a retrogressive tendency. It is 

 not so. What I have desired to insist on is that organism is a 

 fact which encounters the biologist at every step in his investi- 

 gations ; that in referring it to any general biological principle, 

 such as adaptation, we are only referring it to itself, not 

 explaining it ; that no explanation will be attainable until the 

 conditions of its coming into existence can be subjected to 

 experimental investigation so as to correlate them with those of 

 processes in the non-living world. 



Those who were present at the meeting of the British Associ- 

 a'ion at Liverpool, will remember that then, as well as at sosie 

 subsequent meetings, the question whether the conditions 

 necessary for such an inquiry could be realised w.is a burning 

 one. This is no longer the case. The patient endeavours which 

 were made about that time to obtain experimental proof of what 

 was called atiogenesis, although they conduced materially to 

 that better knowledge which we now possess of the conditions 

 of life of bacteria, failed in the accomplishment of their purpose. 

 The question still remains undetermined ; it ha«, so to speak, 

 been adjourned sine die. The only approach to it lies at present 

 in the investigation of those rare instances in which, although 

 the relations between a living organism and its environment 

 ceases as a watch stops when it has not been wound, these 

 relations can be re-established — the process of life reawakened 

 — by the application of the required stimulus. 



I was also desirous to illustrate the relation between physi- 

 ology and its two neighbours on either side, natural philosophy 

 (including chemistry) and psychology. As regards the latter, I 

 need add nothing to what has already been said. As regards 

 the former, it may be well to notice that although physiology 

 can never become a mere branch of applied physics or chemistry, 

 there are parts of physiology wherein the principles of these 

 sciences may be applied directly. Thus, in the beginning of 

 the century. Young applied his investigations as to the move- 

 ments of liquids in a system of elastic tubes, directly to the 

 phenomena of the circulation ; and a century before, Borelli 

 successfully examined the mechanisms of locomotion and the 

 action of muscles, without reference to any, excepting me- 

 chanical principles. Similarly, the foundation of our present 

 knowledge of the process of nutrition was laid in the researches 

 of Bidder and Schmidt, in 1851, by determinations of the 

 weight and composition of the body, the daily gain of weight 

 by food or oxygen, the daily loss by the respiratory and other 

 discharges, all of which could be accomplished by chemical 

 means. But in by far the greater number of physiological in- 

 vestigations, both methods (the physical or chemical and the 

 physiological) mu?t be brought to bear on the same question — 

 to co-operate for the elucidation of the same problem. In the 

 researches, for example, which during several years have occu- 

 pied Prof. Bohr, of Copenhagen, relating to the exchange of 

 gases in respiiation, he has shown that factors purely physical '. 

 — namely, the partial pressures of oxygen and carbon dioxide 

 in the blood which flows through the pulmonary capillaries — 

 are, so to speak, interfered with in their action by the " specific 

 energy " of the pulmonary tissue, in such a way as to render 

 this fundamental process, which, since Lavoisier, has justly 

 been regarded as one of the most important in physiology, 

 much more complicated than we for a long time supposed it to 

 be. In like manner Heidenhain has proved that the process of 

 lymphatic absorption, which before we regarded as dependent 

 on purely mechanical causes — i.e. differences of pressure — is 

 in great measure due to the specific energy of cells, and that in 

 various processes of secretion the principal part is not, as we 

 were inclined not many years ago to believe, attributable to 

 liquid diffusion, but to the same agency. I wish that there had 

 been time to have told you something of the discoveries which 

 have been made in this particular field by Mr. Langley, who 

 has made the subject of "specific energy" of secreting-cells 

 his own. It is in investigations of this kind, of which any 

 number of examples could be given, in which vital reactions 

 mix themselves up with physical and chemical ones so intimately 



NO. 1246, VOL. 48] 



that it is difficult to draw the line between them, that the- 

 physiologist derives most aid from whatever chemical and" 

 physical training he may be fortunate enough to possess. 



There is, therefore, no doubt as to the advantages which 

 physiology derives from the exact sciences. It could scarcely 

 be averred that they would benefit in anything like the same 

 degree from closer association with the science of life. Never- 

 theless, there are some points in respect of which that science 

 may have usefully contributed to the advancement of physics or 

 of chemistry. The discovery of Graham as to the characters of 

 colloid substances, and as to the diffusion of bodies in solution 

 through membranes, would never have been made had not 

 Graham "ploughed," so to speak, " with our heifer." The 

 relations of certain colouring matters to oxygen and carbon 

 dioxide would have been unknown, had no experiments been 

 made on the respiration of animals and the assimilative process 

 in plants ; and, similarly, the vast amount of knowledge which 

 relates to the chemical action of ferments must be claimed as of 

 physiological origin. So also there are methods, both physical 

 and chemical, which were originally devised for physiological 

 purposes. Thus the method by which meteorological pheno- 

 mena are continuously recorded graphically, originated from 

 that used by Ludwig (1847) in his " Researches on the Circu- 

 lation " ; the mercurial pump, invented by Lothar Meyer, was 

 perfected in the physiological laboratories of Bonn and Leip- 

 zig : the rendering the galvanometer needle aperiodic by 

 damping was first realised by du Bois-Reymond — in all of 

 which cases invention was prompted by the requirements of 

 physiological research. 



Let me conclude with one more instance of a different kind, 

 which may serve to show how, perhaps, the wonderful ingenuity 

 of contrivance which is displayed in certain organised structures 

 — the eye, the ear, or the organ of voice — may be of no less 

 interest to the physicist than to the physiologist. Johannes 

 Miiller, as is well known, explained the compound eye of 

 insects on the theory that an erect picture is formed on the 

 convex retina by the combination of pencils of light, received 

 from different parts of the visual field through the eyelets (om- 

 matidia) directed to them. Years afterwards it was shown that 

 in each eyelet an image is formed which is reversed. Con- 

 sequently, the mosaic theory of Miiller was for a long period 

 discredited on the ground that an erect picture could not be 

 made up of " upside-down " images. Lately the subject has 

 been reinvestigated, with the result that the mosaic theory has 

 regained its authority. Prof. Exner' has proved photographi- 

 cally that behind each part of the insect's eye an erect picture 

 is formed of the objects towards which it is directed. There is^ 

 therefore, no longer any difficulty in understanding how the 

 whole field of vision is mapped out as consistently as it is 

 imaged on our own retina, with the difference, of course, that 

 the picture is erect. But behind this fact lies a physical ques» 

 tion — that of the relation between the erect picture which \& 

 photographed and the optical structure of the crystal cones 

 which produce it — a question which, although we cannot now 

 enter upon it, is quite as interesting as the physiological 

 one. 



With this history of a thiory which, after having been for 

 thirty years disbelieved, has been reinstated by the fortunate 

 combination of methods derived from the two sciences, I will 

 conclude. It may serve to show how, though physiolog)' can 

 never become a part of natural philosophy, the questions we 

 have to deal with are cognate. Without forgetting that every 

 phenomenon has to be regarded with reference to its useful 

 purpose in the organism, the aim of the physiologist is not to- 

 inquire into final causes, but to investigate processes. His 

 question is ever How, rather than Why. 



May I illustrate this by a simple, perhaps too trivial, story, which 

 derives its interest from its having been told of the childhood of 

 one of the greatest natural philosophers of the present century?* 

 He was even then possessed by that insatiable curiosity which is 

 the first quality of the investigator ; and it is related of him that 

 his habitual question was "What is the ^o of it ?" and if the 

 answer was unsatisfactory, " What is the particular go of it? 

 That North Country boy became Prof Clerk Max«ell. The 

 questions he asked are those which in our various ways we are 

 all trying to answer. 



1 Exner, "Die Physiologic der facettirten Augen von Krebsen u. lo- 

 secten," Leipzig. 1891. 



2 "Life of Clerk Maxwell " (Campbell and Garnetl), p. >8. 



