6 THE NEW PHYSIOLOGY. 



However difficult it may be to imagine physico- 

 chemical explanations of such processes as respiratory 

 exchange, secretion, muscular activity, etc., there is 

 nothing in the known facts relating to each process taken 

 by itself to preclude the possibility of such explanations. 

 Let us then follow the Euclidean method and assume, 

 provisionally, that they are nothing but physico-chemical 

 processes. This assumption evidently implies that each 

 of the living cells concerned has a very complex and 

 definite structure varying according to its functions. 

 To take an example, a secreting cell in the kidney may 

 be assumed to have a structure which responds to the 

 stimulus of a certain percentage of urea or sodium 

 chloride in the blood, and reacts in such a manner that 

 energy derived from oxidation is so directed as to perform 

 the work of taking up urea or sodium chloride from the 

 blood and transferring it against varying osmotic pres- 

 sures from one side of the cell to the other. This mechan- 

 ism must also be assumed to have the property of main- 

 taining itself in working order, and probably also of 

 reproducing itself under appropriate stimuli, besides 

 also performing various other functions. Its physico- 

 chemical structure must thus be very definite and com- 

 plex to an extent which the older physico-chemical 

 theories took no account of. If we look to the cells in 

 other parts of the body, we are met with the same neces- 

 sity for assuming complexities of structure which seem 

 to grow in extent with every advance in physiological 

 knowledge, every discovery of new substances present 

 within or around the cells, every discovery of new 

 physiological reactions. 



Let us not lose courage, however, but continue to 



