70 THE NEW PHYSIOLOGY. 



be the amount of oxidation, since only a limited amount 

 of oxidation is under the direct control of the vital force. 

 He gave special attention to the elimination of urea and 

 other products of nitrogenous oxidation, and introduced 

 methods of measuring the nitrogenous waste. It was 

 found, apparently in direct confirmation of his general 

 ideas, that the amount of urea excreted rises and falls, 

 except for a certain starvation minimum, in direct pro- 

 portion to the amount of albuminous food eaten. The 

 excess over the starvation minimum was looked upon 

 as " luxus consumption" — an ungoverned oxidation 

 due to .simple chemical factors. 



But the matter was soon carried further by the physio- 

 logists — particularly by Pfluger, and by Voit and his 

 pupil Rubner. It was found that, other conditions being 

 equal, the consumption of oxygen is within wide limits 

 independent of the abundance of its supply, and that 

 the actual consumption of oxygen per unit of body 

 weight is very little different during starvation from 

 what it is when abundant food is supplied. In starva- 

 tion more fat is being oxidised to compensate for the 

 deficiency in albuminous oxidation. Finally, the brilliant 

 work of Rubner established the fundamental fact that 

 within very wide limits different food substances are 

 simply substituted for one another within the organism 

 in direct and exact proportion to the energy which they 

 furnish when broken down. The energy liberation per 

 unit body weight is practically constant, but if excess of 

 food is taken, the excess of potential energy is stored up 

 as fat and glycogen, while if food is withheld, the stored 

 excess is used up. Even when all the stored fat and 

 glycogen is used up, the organism finally flings its own 



