tHESIDENTIAL ADDRESS. 869, 



of identity Whlck hus been ti'acud through the plieiiomoiia just referred to seems 

 to me to have proved a real scientific clue. 



As another example 1 may perhaps be allowed to refer shortly to the regula- 

 tion 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 thi-ough the vagus nerves, always liUed 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 

 satisfaction 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 the alveolar air and presumably, therefore, in the arterial 

 blood, constant. In reality, therefore, the lung ventilation is regulated in 

 accordance with the requirements 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 

 accidents of physical structure with other physiological processes. Under the 

 influence of mechanistic theories the blood-pressure and rate of blood-flow 

 through diflerent 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. Evidence 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 requirements. 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 may 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 maintenance 

 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 dis- 

 appear: for the structure no less than the activity of each part must be deter- 

 mined by its relations to the structure and activities of other parts in the organic 

 whole of the living organism. AVe can investigate these relations, just as we 

 investigate the connection of secretion with respiratory exchange, circulation, or 

 the composition of the blood ; and they must evidently be physiological relations. 

 Our aim is not the hopeless one of giving a physico-chemical explanation of the 

 development and maintenance of organic structure, but simply to discover the 

 physiological relations which determine the structure of each part and its main- 

 tenance. Many facts bearing on this subject have recently been brought to light 

 by the application of experimental methods to embryology, and by 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 deal- 

 ing with the chemistry of the body will be required. 



It was in connection with 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 difficulty remains of reconciling the fundamental conceptions of 

 Biology with those of Physics and Chemistry. This is, however, a matter of 

 which the discussion must be handed over to Philosophy, which has many similar 

 matters to deal with. If it is a fundamental axiom that an organism actively 



