TENDENCY OF PHYSIOLOGICAL PROGRESS 37 



physical and chemical conditions which deter 

 mine excitation and excitability, taking these 

 words in their widest sense as applying to 

 the whole of the elementary phenomena 

 with which physiology and morphology deal, 

 has grown continuously, and will continue 

 to grow. No physiological or morphological 

 phenomenon is beyond investigation on similar 

 lines ; but the results of such investigation 

 are by no means identical with the gradual 

 establishment of a definite causal connection 

 between stimulus and response. There has 

 been much unconscious confusion on this 

 point. 



We must now proceed to examine the 

 belief, at present very prevalent, that the 

 progress of physiology is leading to a gradual 

 verification of the mechanistic theory of life. 

 It has already been pointed out how depend 

 ent the progress of biology, and particularly 

 of physiology, has been on that of physics 

 and chemistry. This undoubted fact has 

 been taken as evidence that physiology is 

 becoming a physical and chemical science, 

 and has commonly been coupled with the 

 assertion that with the help of these methods 



