DEFECTS OF VITALISM 25 



present, the organism selects just what it 

 requires for its growth and maintenance, re 

 jecting or excreting all that is superfluous. 



Let us examine the matter more closely, 

 however. The further physiological investi 

 gation is carried, the more clearly does it 

 appear that the co-ordinated action by which 

 different parts of an organism work together 

 for the maintenance of the whole depends on 

 chemical substances or physical disturbances 

 conveyed from part to part of the living 

 substance. The behaviour of each part is 

 not merely qualitatively, but also quantita 

 tively dependent on these chemical and 

 physical influences. The respiratory centre 

 responds to the minutest alterations in the 

 partial pressure of carbon dioxide in the 

 blood, and the kidney to the smallest varia 

 tions in the concentrations of water or 

 sodium chloride or hydrogen ions. Every 

 where in the living body we find, on close 

 examination, this close and accurate depend 

 ence of vital activity on the physical and 

 chemical conditions in the immediate environ 

 ment. It is, therefore, only from an outside 

 and superficial point of view that there 



