EXCHANGE OF MATERIAL. 461 



equilibrium, but may even add to the store of bodily proteids, while 

 in a lean body with food containing the same amount of proteids 

 and fat there would be a loss of proteids. In a body rich in fat a 

 greater amount of proteids is protected from metabolism by a cer- 

 tain quantity of fat than in a lean body. 



Because of the sparing action of fats an animal by the addition 

 of fat to its food may, as is apparent from the tables, increase its 

 proteid condition with a quantity of meat which is insufficient to 

 preserve nitrogenous equilibrium. The proportion of proteids 

 and fats in the food is of the greatest importance in regard to in- 

 creasing the proteids of the body. With an exclusively proteid diet 

 the metabolism of proteids increases with the increased amount 

 of proteids in the food, and this behavior is not prevented by the 

 addition of fat to the food, even though the absolute extent of the 

 metabolism of proteids is somewhat diminished. In the presence 

 of a great deal of proteid in proportion to the fat of the food, very 

 large quantities of proteid are necessary for the maintenance of 

 nitrogenous equilibrium, as well as for an increase of proteid, while 

 by the addition of a relatively large amount of fat to the proteids 

 such a result is reached even with comparatively small amounts of 

 proteids. The following table will elucidate this point: 



TABLE VIII. 



Food. Flesh. 



Meat. Fat. Metabolized. On the Body. 



450 250 344 -f- 106 



1000 250 875 +125 



1500 250 1381 +119 



The table shows that also in the presence of fat the proteid de- 

 struction decreases with increased amounts of proteids in the food, 

 and that, because of this, in the given examples no essentially in- 

 creased metabolism of proteid is obtained with a diet of 1500 grms. 

 meat and 250 grms. fat than with 450 grms. meat and the same 

 quantity of fat. The importance of this fact will be spoken of 

 later. 



If the quantity of meat in the food is kept constant by feeding 

 with meat and fat, while the fat varies, then the destruction of pro- 



