2 THE NEW PHYSIOLOGY. 



that I have carefully pondered over these reasons during 

 many years of active physiological work. 



When we look back on the history of physiology, it 

 seems perfectly evident that physiological progress has 

 been dependent on the progress of physics and chemistry. 

 On this point there is no room for doubt. To take only 

 one example, where should we be in the investigation of 

 animal metabolism but for the ideas and experimental 

 methods furnished to us by physics and chemistry ? 

 We should know next to nothing about respiration, 

 animal heat, nutrition, or muscular and other work. 

 Physiology depends at every turn on physics and 

 chemistry, and its future progress will certainly be 

 equally dependent on advances in physical and chemical 

 knowledge. This consideration has, I imagine, weighed 

 very heavily in the minds of those physiologists who 

 have concluded that physiology is nothing but applied 

 physics and chemistry. A further fact which weighs 

 equally heavily is that in spite of diligent search nothing 

 contradicting the fundamental laws of conservation of 

 matter and energy has been discovered in connection 

 with living organisms. 



When, however, we ask what progress has been made 

 towards the physico-chemical explanation of physio- 

 logical processes, we at once enter upon controversy. 

 We may point to advances in some directions, but they 

 are accompanied by the appearance of unforeseen diffi- 

 culties in other directions. Again, to take animal meta- 

 bolism as a typical instance, the investigations of the 

 last hundred and twenty years have enabled us to assign 

 ultimate physical and chemical sources to the energy 

 and material leaving the body in various forms. We 



