4 THE NEW PHYSIOLOGY. 



protein, and from day to day the amount of energy 

 liberated in the body is very steady. With regard to 

 the excretion of material by the kidneys a similar growth 

 in knowledge can be traced. It is scarcely a century 

 since the urine was regarded as equivalent more or less 

 to the liquid part of the blood separated from the 

 corpuscles, which were unable to pass through the very 

 fine capillary tubules supposed to exist in the kidney 

 substance. Gradually, however, we have learnt how 

 extraordinarily delicate is the selective action which 

 occurs in the kidney substance, and how efficiently this 

 selective action maintains the normal composition of 

 the blood. Scarcely a remnant is now left of the old 

 filtration theories. Our ideas of tissue nutrition and 

 growth have undergone a similar change ; and it is hard 

 to realise that only about seventy years ago Schwann 

 could put forward the theory that cell formation and 

 growth is a process of crystallisation. 



One can multiply instances like these almost inde- 

 finitely ; but I have, perhaps, said enough to show that 

 if in some ways the advance of physiology seems to have 

 taken us nearer to a physico-chemical explanation of 

 life, in other ways it seems to have taken us further 

 away. On the one hand, we have accumulating know- 

 ledge as to the physical and chemical sources and the 

 ultimate destiny of the material and energy passing 

 through the body : on the other hand, an equally rapidly 

 accumulating knowledge of an apparent teleological 

 ordering of this material and energy ; and for this teleo- 

 logical ordering we are at a loss for physico-chemical 

 explanations. There was a time, about fifty years ago, 

 when the rising generation of physiologists in their 



