THE NEW PHYSIOLOGY. 55 



only a special application of ordinary physics and 

 chemistry became firmly established, and is still what 

 may be called the orthodox creed of physiologists. It 

 may be truly said that most physiologists look upon 

 this creed as something which has been established for 

 all time, and that they would be inclined to regard any 

 deviation from it as harmful scientific heresy. Neverthe- 

 less I think that we have again reached a turning-point, 

 and that a new physiology is arising in place of the 

 physico-chemical physiology which has held sway for 

 so many years. I propose in this lecture to give some 

 account of how, as it seems to me, this new physiology 

 is shaping itself. 



It is natural for us to assume that the aim of all 

 investigations in physiology must be to ascertain the 

 causes of physiological activity. However complex a 

 physiological reaction may be, the conditions which 

 determine it can be investigated experimentally ; and 

 from long experience we can be quite certain that such 

 experimental investigation will always lead to some 

 result, however obscure. There is, and can be, no limit 

 to experimental investigation of causes. When, how- 

 ever, we examine the results obtained by experimental 

 physiology there emerges a point in which they differ 

 greatly from the results ordinarily obtained in the 

 investigation of inorganic phenomena : for it is char- 

 acteristic of physiological reactions that they are de- 

 pendent to an extreme degree on all sorts of environing 

 conditions. We recognise this when we speak of stimulus 

 and response rather than of cause and effect. When 

 the light from a star is focussed on the retina there is a 

 physiological response by night, but none by day. The 



