FATS, CARBOHYDRATES, AND ALBUMINS. 



343 



determine anew the quantity of albumin which is absolutely necessary to 

 prevent injury to the albumin content of the organism. This amount of 

 albumin will be much less than is required in a diet of albumin alone. If 

 we feed an animal a definite quantity of fat and albumin, it will be possible 

 to reduce the albumin requirement more and more by increasing the pro- 

 portion of fat in mixture. We finally reach a minimum amount of pro- 

 tein, and if we attempt to replace it by fat, we cause the body albumin 

 itself to be attacked. This limit varies with different animals and at 

 different times with the same animal; in every organism it is dependent 

 upon the condition of the body, and, above all, upon the fat in the body at 

 the time of the experiment. A fat animal will permit more albumin to be 

 replaced by fat than will a lean one, for the former can contribute from 

 its own supply of fat. On the other hand, by feeding fat we have a means 

 of causing an accumulation of albumin. We can spare albumin not only 

 with fat, but also with carbohydrates. By their assistance also, provided 

 sufficient albumin is supplied, the albumin content of the body may be 

 increased. Voit, 1 who performed experiments in this direction, came to 

 the conclusion that the fats and carbohydrates did not have an equivalent 

 effect in causing an accumulation of albumin. Carbohydrates are more 

 efficient as " albumin sparers " than are the fats, as is shown by the follow- 

 ing table: 



Atwater 2 has recently determined accurately the comparative values of 

 carbohydrates and fats as sparers of albumin. The fact that proteins are 

 distinguished from the other nutrients by the amount of nitrogen which 

 they contain, makes it easy to carry out the experiment. By simply 

 comparing the amount of nitrogen in the food with that of the urine, we 

 can at once get an idea as to how much albumin has been decomposed. 

 The nitrogen content of the faeces tells us approximately how much albumin 

 has not been absorbed. We speak of a " nitrogen equilibrium " when the 

 amount of nitrogen ingested in the form of food is equal to that con- 

 tained in the urine and in the faeces. If the latter is greater than the 



1 Carl Voit: Hermann's Handbuch der Physiologic, 6, 143 (1881). 2 loc. dt. 



