September 23, 1909] 



NA TURE 



385 



ing of the Association may be regarded as an annual 

 mission in whicli an attempt is made to bring the latest 

 results of scientific investigation into the daily routine of 

 the life of the community. 



We physiologists, as men who are laying the foundation 

 on whicli medical knowledge must be built, have as our 

 special preoccupation the study of man. Although every 

 animal, and indeed every plant, comes within the sphere 

 of our investigations, our main object is to obtain from 

 such comparative study facts and principles which will 

 •enable us to elucidate the mechanism of man. In this 

 task we view man, not as the psychologist or the historian 

 ■does, by projecting into our object of study our own feel- 

 ings and emotions, but by regarding him as a machine 

 played upon by environmental events and reacting thereto 

 in a way determined by its chemical and physical struc- 

 ture. 



Can we not learn something of value in our common 

 life by adopting this objective point of view and regard- 

 ing man as the latest result of a continuous process of 

 -evolution which, begun in far-off ages, has formed, proved 

 and rejected myriads of types before man himself appeared 

 on the surface of the globe? 



Aia^iation. 



In his study of living beings, the physiologist has one 

 guiding principle which plays but little part in the sciences 

 of the chemist and physicist, namely, the principle of 

 adaptation. Adaptation or purposiveness is the leading 

 ■characteristic of every one of the functions to which we 

 devote in our text-books the chapters dealing with 

 assimilation, respiration, movement, growth, reproduction, 

 and even death itself. Spencer has defined Ufe as " the 

 continuous adjustment of internal relations to external 

 relations." Every phase of activity in a living being is 

 a sequence of some antecedent change in its environment, 

 and is so adapted to this change as to tend to its neutralisa- 

 tion and so to the survival of the organism. This is what 

 is meant by adaptation. It will be seen that not only 

 does it involve the teleological conception that every 

 normal activity must be for the good of the organism, 

 but also that it must apply to all the relations of living 

 beings. It must therefore be the guiding principle, not 

 only in physiology, with its special preoccupation w'ith 

 the internal relations of the farts of the organism, but 

 also in the other branches of biology, which treat of the 

 relations of the living animal to its environment and of 

 the factors which determine its survival in the struggle 

 for existence. -Adaptation therefore must be the deciding 

 factor in the origin of species and in the succession of the 

 different forms of life upon this earth. 



Origin of Life. 



A living organism may be regarded as a highly unstable 

 • chemical system which tends to increase itself continuously 

 under the average conditions to which it is subject, but 

 undergoes disintegration as a result of any variation from 

 this average. The essential condition for the survival of 

 the organism is that any such disintegration shall result 

 in so modifying the relation of the system to the environ- 

 ment that it is once more restored to the average in which 

 assimilation can be resumed. 



We may imagine that the first step in the evolution of 

 life was taken w'hen, during the chaotic chemical inter- 

 changes which accompanied the cooling down of the 

 molten surface of the earth, some compound was formed, 

 probably w-ith absorption of heat, endowed with the pro- 

 perty of polymerisation and of grow^th at the expense of 

 surrounding material. Such a substance could continue to 

 grow only at the expense of energy derived from the 

 surrounding medium, and would undergo destruction with 

 any stormy change in its environment. Out of the many 

 such compounds which might have come into being, only 

 such would survive in which the process of exothermic 

 ■disintegration tended towards a condition of greater 

 stability, so that the process might come to an end spon- 

 taneously and the organism or compound be enabled to 

 await the more favourable conditions necessary for the 

 continuance of its growth. With the continued cooling 

 of the earth, the new production of endothermic com- 

 pounds would probably become rarer and rarer. The 

 beginning of life, as we know it, was possibly the forma- 

 NO. 2082, VOL. 81] 



tion of some complex, analogous to the present chlorophyll 

 corpuscles, with the power of absorbing the newly pene- 

 trating sun's rays and of utilising these rays for the endo- 

 thermic formation of further unstable compounds. Once 

 given an unstable system such as we have imagined, with 

 two phases, viz. (i) a condition of assimilation or growth 

 by the endothermic formation of new material ; (2) a con- 

 dition of " exhaustion," in which the exothermic destruc- 

 tive changes excited by unfavourable external conditions 

 came to an end spontaneously — the great principle of 

 natural selection or survival of the fittest would suffice to 

 account for the evolution of tlie ever-increasing complexity 

 of living beings which has occurred in the later history 

 of this globe. The adaptations, i.e. the reactions of the 

 primitive organism to changes in its environment, must 

 become continually more complex, for only by means of 

 increasing variety of reaction can the stability of the system 

 be secured within greater and greater range of external 

 conditions. The difference between higher and lower forms 

 is therefore merely one of complexity of reaction. 



The naked protoplasm of the plasmodium of Myxo- 

 mycetes, if placed upon a piece of wet blotting-paper, will 

 crawl towards an infusion of dead leaves, or away from 

 a solution of quinine. It is the same process of adapta- 

 tion, the deciding factor in the struggle for existence, 

 which impels the greatest thinkers of our times to spend 

 long years of toil in the invention of the means for the 

 offence and defence of their community or for the protec- 

 tion of mankind against disease and death. The same law 

 which determines the downward growth of the root in 

 plants is responsible for the existence to-day of all the 

 sciences of which mankind is proud. 



The difference between higher and lower forms is thus 

 not so much qualitative as quantitative. In every case, 

 whatever part of the living world we take as an example, 

 we find the same apparent perfection of adaptation. 

 Whereas, however, in the lower forms the adaptation is 

 within strictly defined limits, with rise in type the range 

 of adaptation steadily increases. Especially is this marked 

 if we take those groups which stand, so to speak, at the 

 head of their class. It is therefore important to try and 

 find out by a study of various forms the physiological 

 mechanism or mechanisms which determine the increased 

 range of adaptation. By thus studying the physiological 

 factors, which may have made for success in the struggle 

 for dominance among the various representatives of the 

 living world, we may obtain an insight into the factors 

 which will make for success in the further evolution that 

 our race is destined to undergo. 



It is possible that, even at this time, objections may be 

 raised to the application to man of conclusions derived 

 from a study of animals lower in the scale. It has indeed 

 been urged, on various grounds, that man is to be re- 

 garded as exempt from the natural laws which apply to 

 all other living beings. When we inquire into the grounds 

 for assuming this anomic, this outlawed condition of man, 

 we generally meet with the argument that man creates his 

 own environment and cannot therefore be considered to be 

 in any way a product of it. This modification or creation 

 of environment is, however, but one of the means of 

 adaptation employed by man in common with the whole 

 living kingdom. From the first appearance of life on the 

 globe we find that one of the methods adopted by organisms 

 for their self-preservation is the production of some artificial 

 surroundings which protect them from the buffeting of 

 environmental change. What is the mucilaginous envelope 

 produced by micro-organisms in presence of an irritant, or 

 the cuticle or shell secreted by the outermost cells of an 

 animal, but the creation of such an environment? All 

 unicellular organisms, as well as the units composing the 

 lowest metazoa, are exposed to and have to resist every 

 change in concentration and composition of the surround- 

 ing water. When, however, a body cavity or coelom. 

 filled probably at first with sea-water, made its appear- 

 ance, all the inner cells of the organism were withdrawn 

 from the distributing influence of variations in the 

 surrounding medium. The coslomic fluid is renewed and 

 maintained uniform in composition by the action of the 

 organism itself, so that we may soeak of it as an environ- 

 ment created by the organism. The formation of a body 

 cavitv filled with salt solution at once increased the range 

 of adaptation of the animals endowed therewith. Thus 



