36 DISCHARGE OF NITROGEN. 



" nitrogen equilibrium," it is necessary that the daily weight 

 of nitrogen absorbed should not fall below a certain limit, 

 determinable in respect of each species of animal by ex- 

 periment. In man the minimum daily allowance of N is 

 .about 1 5 grammes, or O'O2 per cent, of the body-weight ; 

 in the carnivora about O'l per cent. ; in the ox 0*005 per 

 cent. (Henneberg). 



When the diet consists of proteid exclusively, a larger 

 quantity is required for the maintenance of the equi- 

 librium than when it also contains fat or carbohydrates. 

 Accordingly, in those animals or races of mankind whose 

 food consists largely of either of these constituents par- 

 ticularly the latter the nitrogen requirement is lower than 

 in others. The reason why this is so is not understood. 



When the animal body is deprived of food, its " stored 

 proteid " rapidly disappears. During this process (the 

 first stage of inanition, and which lasts a few days only) 

 the nitrogen discharge as rapidly diminishes. During the 

 second stage it continues to diminish, but only in pro- 

 portion to the diminution of the total body-weight. 



In an animal fed exclusively with flesh the nitrogen 

 discharge at first increases pari passu with the absorption 

 of proteid, the absorption of O being increased in exact 

 proportion to the increase which has taken place in the 

 quantity of material to be disintegrated, so that the 

 respiratory quotient remains nearly unaltered (Bidder and 

 Schmidt). Although, however, the overfed animal main- 

 tains its nitrogen equilibrium, it usually gains weight, and 

 therefore must " lay on " fat. 



Relation of Muscular Work to the Discharge of Nitrogen 

 and Carbon. The chemical changes on which the per- 

 formance of work by muscle depends, manifest themselves 

 in the production of CO 2 and H 2 O. Consequently, in 

 muscular exertion both constituents of the "insensible 

 loss " are so augmented that (irrespectively of the 

 secondary effect produced on the skin) they more than 



