October i, 19c 8] 



JVA TURE 



555 



Let us now see how the conception just defined can be 

 used as a scientific working hypothesis. In accordance with 

 it any form of physiological activity is presumably related 

 essentially, and not accidentally, to the other details of 

 activity and structure in the same organism. Stated 

 generally, therefore, the problem of Physiology is not to 

 obtain piecemeal physico-chemical explanations of phy- 

 siological processes, but to discover by observation and 

 experiment the relatedness to one another of all the details 

 of structure and activity in each organism as expressions 

 of its nature as an organism. 



The first step in physiological or morphological discovery 

 is to observe the bare sensuous fact of some detail of 

 physical or chemical change, or of composition or structure, 

 . in connection with an organism. It is only, however, when 

 we find that this detail is not accidental that it becomes 

 of biological interest. AVe can observe its constancv or 

 otherwise in the same organism or similar organisms — that 

 is to say, the constancy of its relations to other details 

 of structure and activity. Or we can by experiment search 

 for the element of constancy when it is at first sight hidden 

 from our view. In so far as we find this, it seems to me 

 that we reach physiological or biological explanation ; but 

 evidently the process of reaching it is at anv stage in 

 knowledge only imperfectly realised, since new details of 

 activity and structure are constantly being revealed. 



Concrete examples will make the matter clearer, and I 

 shall first take as an example the progress of knowledge 

 ill relation to animal heat. It was of course common 

 knowledge from early times that in the higher animals a 

 certain amount of warmth in the bodv is present during 

 life. With the invention of the thermometer the body- 

 temperature could be measured, and its extraordinarv con- 

 stancy observed. When Lavoisier measured the heat- 

 production of an animal, and compared the output of 

 heat with the output of carbon dioxide and disappearance 

 of oxygen in respiration, an immense step forward was 

 taken. This step was in two distinct respects a very 

 great one. In the first place it revealed an element of 

 identity between organic and inorganic phenomena, since 

 heat-production in an animal was shown to be accompanied 

 by chemical changes quantitatively identical with those 

 accompanying heat-production by oxidation outside the 

 body. In the second place, and from the distinctively 

 physiological point of view, it revealed a fundamental 

 relation between heat-production, respiratorv exchange, 

 and the consumption of food. 



.As regards the first of these points I should like to say 

 definitely that I, for one, firmly believe that could we 

 only understand them fully we could bring organic and 

 inorganic phenomena under the same general conceptions. 

 Lavoisier's discovery, like that of Mayer in relation to 

 the sources of muscular energy, was a great advance in 

 this direction. But this is a very different thing from an 

 advance in the direction of rendering life intelligible in 

 terms of phvsico-chemical conceptions as we commonly 

 understand them. Lavoisier's discoveries did nothing in 

 the direction of reducing to physico-chemical terms the 

 apparent teleologica! or, as I should prefer to say, 

 " physiological " element in the phenomena of animal heat. 

 It is to the second point that I wish to direct special 

 attention at present. Lavoisier's discovery rnpidlv brought 

 the phenomena of animal heat into direct relation, not onlv 

 with respiration but with nutrition, circulation of blood, 

 excretion, and other processes ; and it was gradually dis- 

 covered that the maintenance of a constant bodv-tempera- 

 tore renders physiologically intelligible a large number of 

 phenomena in connection with difTerent bodily activities — 

 for instance, increased metabolism with fall of external 

 temperature, sweating or increased circulation through the 

 skin with muscular work, the relative constancy of meta- 

 bolism during starvation, and the physiological equivalence 

 of proteid, carbohydrate, and fat in proportion to their 

 energy values. These phenomena are intelligible on the 

 assumption that warm-blooded animals actively maintain a 

 certain body-temperature, just as they maintain a certain 

 bodilv structure and composition. This mode of explana- 

 tion is not a physico-chemical one. but I venture very con- 

 fidently to assert that it is a physiological one, and in fact 

 the only kind of explanation which reallv interests and 

 appeals to a true physiologist. The thread of identity 



NO. 2031, VOL. 78] 



which has been traced through the phenomena just referred 

 to seems to me to have proved a reaL scientific clue. 



.As another example I may perhaps be allowed to refer 

 shortly to the regulation of breathing, as this is a subject 

 on which I have recently been working. Current accounts 

 of the clock-like action of the respiratory centre during 

 normal breathing, with the expansion and contraction of 

 the lungs acting as a sort of governor through the vagus 

 nerves, always filled me with suspicion, as it seemed to 

 me that such a regulation was altogether unlike a 

 physiological one. This led me to investigate the matter 

 further, along with Mr. Priestley ; and we had the satisfac- 

 tion of being able to prove that the ventilation of the 

 lungs is actually regulated with exquisite exactness, in 

 such a way as to keep the partial pressure of carbon 

 dioxide in tlic alveolar air and presumably, therefore, in the 

 arterial blood, constant. In reality, therefore, the lung 

 ventilation is regulated in accordance with the require- 

 ments of respiratory exchange; and what seems to be true 

 physiological explanation has been advanced a short stage. 



The advance of knowledge with regard to the circulation 

 might be made the text of a similar discourse. By a process 

 of abstraction the circulation of the blood may be regarded 

 as a mere mechanical process, connected only by the acci- 

 dents of physical structure with other physiological processes'. 

 Under the influence of mechanistic theories the blood- 

 pressure and rate of blood-flow through different organs 

 were indeed for long supposed to be the primary deter- 

 mining cause of the physiological activities of these organs, 

 just as the rate and depth of breathing were supposed to 

 determine the consumption of oxygen by the body. Evi- 

 dence is, however, accumulating on all hands that the 

 blood-supply to various parts, like the air-supply to the 

 lungs, is in reality determined by physiological require- 

 ments. In other words, it is a direct expression of the 

 nature of the organism, just as the common-sense idea 

 of life would lead us to expect. 



I mav pass next to a branch of physiological knowledge 

 which is still in its early infancy. Under the influence of 

 mechanistic ideas Physiology has for long left completely 

 out of account investigation into the formation and main- 

 tenance of organic structure. For mechanistic explanations 

 structure had to be assumed, and as a consequence anatomy 

 was left high and dry in a position of helpless isolation. 

 If. however, the real aims of Physiology are those which 

 I have tried to indicate, the separation between Physiology 

 and .Anatomy must tend to disappear : for the structure no 

 less than the activity of each part must be determined b' 

 its relations to the structure and activities of other parts 

 in the organic whole of the living organism. We can 

 investigate these relations, just as we investigate the con- 

 nection of secretion with respiratory exchange, circulation, 

 or the composition of the blood ; and they must evidently 

 be phvsiological relations. Our aim is not the hopeless one 

 of giving a physico-chemical explanation of the develop- 

 ment and maintenance of organic structure, but simply 

 discover the phvsiological relations which determine the 

 structure of ea/h part and its maintenance. Many facts 

 bearing on this subject have recently been brought to light 

 bv the application of experimental methods to embryology, 

 and bv the study of reproduction of lost or injured parts, 

 and of grafting : also by the study of so-called " internal 

 secretion " in connection with various organs. It seems 

 clear, however, that we are only at the beginning of a vast 

 development of knowledge in this direction, and that for 

 this development far more refined methods of dealing with 

 the chemistry of the body will be required. 



It was in connection wi(h the facts of reproduction and 

 heredity that the difficulties of the mechanistic theory of 

 life were found finally to culminate. For the distinctively 

 biological theory of life, to which I have endeavoured to 

 give some definition, these difficulties do not exist. They 

 are, it is true, not solved ; but they are set aside as being 

 due to wrong initial assumptions and therefore purely 

 artificial. The difficultv remains of reconciling the funda- 

 mental conceptions of Biology with those of Physics and 

 Chemistry. This is, however, a matter of which the di.s- 

 cussion must be handed over to Philosophy, which has 

 many similar matters to deal with. If it is a fundamental 

 axiom that an organism actively asserts or maintains a 

 specific structure and specific activities, it is clear that 



