868 THANSACTIOiVS OF SECTION I. 



■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 physiological 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 lind that this detail is not accidental that it becomes of biological 

 interest. We can observe its constancy 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 any 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 in 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 body is present during life. "With the invention of the 

 thermometer the body-temperature could be measured, and its extraordinary 

 constancy 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 ot" view, it revealed a fundamental relation between heat-production, 

 respiratory exchange, and the consumption of food. 



As regards the first of these points I should like to say definitely that I, for 

 one, iirmly 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 physico-chemical 

 conceptions as we commonly imderstand them. Lavoisier's discoveries did 

 nothino- in the direction of reducing to physico-chemical terms the apparent 

 teleoloo'ical 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 rapidly brought the phenomena of animal heat into direct 

 relation, not only with respiration but with nutrition, circulation of blood, excre- 

 tion, and other processes ; and it was gradually discovered that the maintenance 

 of a constant body-temperature renders physiologically intelligible a large number 

 of phenomena in connection with different 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 metabolism 

 durino- starvation, and the physiological equivalence of proteid, carbohydrate, 

 and fat in proportion to their energy values. These phenomena are intelligible 

 onthe assumption that warm-blooded animals actively maintain a certain body- 

 temperature, just as they maintain a certain bodily structure and composition. 

 This mode of explanation is not a physico-chemical one, but 1 venture very 

 confidently to assert that it is a physiological one, and in fact the only kind of 

 expLination which really interests and appeals to a true physiologist. The thread 



