RELATION OF PHYSIOLOGY TO PHYSICS. 15 



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 by 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 

 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 physio- 

 logical relations which determine the structure of each 

 part and its maintenance. 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 begin- 

 ning of a vast development of knowledge in this direc- 

 tion, and that for this development far more refined 

 methods of dealing 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 assump- 



