THE NEW PHYSIOLOGY. 69 



tion in the salt-concentration, to the effects of which 

 the secreting cells were reacting. Here, then, we are in 

 presence of another exactly but elastically regulated 

 normal, the slightest deviation from which produces, in 

 the kidneys, a reaction comparable in its exquisite deli- 

 cacy with the reaction of the respiratory centre or liver 

 or kidneys to a change in hydrogen ion concentration. 



The physiology of the kidneys has, in accordance with 

 prevalent physiological conceptions, been attacked from 

 the side of ' causal ' explanation. I know nothing 

 more hopeless than the attempts to explain the out- 

 standing features of secretion of urine on the lines of 

 ordinary physics and chemistry. So far as the facts are 

 yet known, we can, however, get a practical grasp of the 

 kidney activities if we attack the subject from the stand- 

 point of the active maintenance of the normal blood 

 composition. 



Let me turn now to the general physiology of nutrition. 

 In the preliminary stages of investigation of this subject 

 physiology has owed much to the pure chemists, and this 

 debt is constantly increasing. We have only to think 

 of the work of such men as Black, Priestley, Lavoisier, 

 and Liebig. Like Wohler, who synthesis ed urea, Liebig 

 was a convinced vitalist. For him there was a central 

 kernel of vital activity under the control of the " vital 

 force " ; but outside this central kernel he interpreted 

 the phenomena of nutrition on purely chemical lines. 

 He thought of oxygen as something free to oxidise any- 

 thing oxidisable within the body, except what is pro- 

 tected by the vital force ; and he assumed that the greater 

 the concentration of oxygen in the lungs, and the greater 

 the supply of food-material to the body, the greater will 



