THE DEEPENING OF PHYSIOLOGY. 325 



aware of the obstacles to any advance in this (phys- 

 ico-chemical) direction, and there is not the slightest 

 indication that they will be removed, but rather that, 

 with further increase of knowledge, and more re- 

 fined methods of physical and chemical investiga- 

 tion, they will only appear more and more difficult 

 to surmount. . . . All that is really shown by 

 the partial success which has attended the applica- 

 tion of physical and chemical principles of explana- 

 tion in physiology is that in the course of investi- 

 gation it is often possible to ignore for the time the 

 distinctive features of life. For certain scientific 

 purposes we may treat some part of the body as 

 a mechanism, without taking into consideration 

 the manner in which it is controlled and maintained ; 

 and in this way results of great value have been 

 attained. But in doing all this we are deliberately 

 ignoring or abstracting from all that is character- 

 istic of life in the phenomena dealt with. The action 

 of each bodily mechanism, the composition and struc- 

 ture of each organ, the intake and output of energy 

 from the body, are all mutually determined and con- 

 nected with one another in such a way as at once to 

 distinguish a living organism from anything else. 

 As this mutual determination is the characteristic 

 mark of what is living, it cannot be ignored in the 

 framing of fundamental working hypotheses." 



We are lingering over this discussion because of 

 its great historical interest. Again and again some 

 success in discovering physico-chemical sequences in 

 the living organism has awakened the expectation 

 that the dawn of a mechanical theory (interpretation 

 or re-description) of life was drawing nigh. Again 

 and again the expectation has been disappointed, 

 and the investigators have returned to rest in a 



