82 



MAINTENANCE RATIONS OF FARM ANIMALS. 



of urea, etc., leaving a nonnitrogenous residue which contains the 

 larger portion of the chemical energy of the protein which it repre- 

 sents and is in condition to be oxidized as fuel material. (Compare 

 pp. 30-32.) 



The increased nitrogen excretion on a high protein diet is sinrply 

 the method by which the organism gets rid of useless nitrogen, while 

 retaining the larger share of the energy of the protein for fuel 

 purposes. In other words the organism when confronted with a 

 protein supply in excess of its needs is able by what seems to be a 

 comparatively simple process to transform it into nonnitrogenous 

 fuel material with but slight loss, getting rid of the useless nitrogen 

 as urea through the urine. The increased nitrogen excretion conse- 

 quent on high protein feeding does not mean the total destruction 

 of the corresponding amount of protein, but simply its transforma- 

 tion into compounds which can serve as sources of energy. 



STORAGE OF PROTEIN. 



In the mature animal a surplus of feed protein is largely katabo- 

 lized, so that a continued increase of the protein tissue of the animal 

 can not be brought about, as can that of the adipose tissue, simply 

 by a surplus in the feed. The protein content of such an animal, 

 however, is not to be regarded as absolutely fixed, so that the protein 

 supply has no effect upon it. On the contrary, a considerable range 

 of variation is possible. 



When the protein supply is increased, nitrogen equilibrium is not established 

 at once, but for a time more or less storage of nitrogenous material takes place. 

 For instance, when a dog in Voit's experiments 1 was changed from a ration 

 of 500 grams of meat daily for 42 days to one of 1,500 grams, the urinary nitro- 

 gen showed the following behavior on the last three days of old feeding and on 

 the first seven of the new : 



Storage of protein by dog — Toit. 





Date. 



Meat fed. 



Nitrogen 

 of feed. 



Nitrogen 

 of urine. 2 



Gain of 

 nitrogen. 





1863. 



Grams. 



Grams. 



Grams. 



Grams. 





May 29 



500 



17.0 



18.9 



-1.9 



Experiment No. 40 



- May 30 



500 



17.0 



18.2 



-1. 



May 31 



500 



17.0 



17.7 



- .7 





June 1 



1,500 



51.0 



41.1 



+9.9 





June 2 



1,500 



51.0 



44.1 



+6.9 





June 3 



1,500 



51.0 



46.9 



+4.1 





June 4 



1,500 



51.0 



48.0 



+3.0 



June 5 



1,500 



51.0 



48.6 



+2.4 





June G 



1,500 



51.0 



48.9 



+2.1 





June 7 



1,500 



51.0 



50.6 



+ -4 



Upon the lighter ration the animal was losing a small amount of protein 

 daily. On the heavier ration there was a diminishing gain for six days, ap- 



1 Zeitsehrift fur Biologie, vol. 3, p. 80. 



2 Computed from Voit's figures for urea. 



