486 DIET OF PURE FAT OR CARBOHYDRATES. 



albumin. The carnivora which can maintain their metabolism in 

 equilibrium by eating a large amount of flesh, can do so with less 

 flesh when gelatin is added to their food. A diet of gelatin alone, 

 which produces much urea, is not sufficient for this purpose, and 

 animals soon lose their appetite for this kind of food (v. Bischoff, v. 

 Voit, v. Pettenkofer, Oerum). 



Owing to the great solubility of gelatin, the value of gelatin as a food used 

 to be greatly discussed, and now again the addition of gelatin in the form of 

 calf s-foot jelly is recommended to invalids. When chondrin is given along with 

 flesh for a time, grape-sugar is found in the urine (Bodeker). 



239. A Diet of Fat or of Carbohydrates. 



If fat alone be given as a food, the animal lives but a short time. 

 The animal so fed secretes even less urea than when it is starving ; 

 so that the consumption of fat limits the decomposition of the animal's 

 own proteids. This depends upon the fact that, fat being an easily 

 oxidised body, yields heat chiefly, and becomes sooner oxidised than 

 the nitrogenous proteids which are oxidised with more difficulty. If 

 the amount of fat taken be very large, all the C of the fat does not 

 reappear, e.g., in the C0 2 of the expired air ; so that the body must 

 acquire fat, whilst at the same time it decomposes proteids. The 

 animal thus becomes poorer in proteids and richer in fats at the same 

 time. 



When carbohydrates alone are given, they must first be converted 

 by the act of digestion into sugar. The result of such feeding 

 coincides pretty nearly with the results of feeding with fat alone. 

 But the sugar is more easily burned or oxidised within the body 

 than the fat, and 17 parts of a carbohydrate are equal to 10 parts 

 of fat. Thus the diet of carbohydrates limits the excretion of 

 urea more readily than a purely fat diet. The animals lose flesh 

 and appear even to use up part of their own fat. 



The direct introduction of grape-sugar and cane-sugar into the blood does not 

 increase the amount of oxygen used, although the amount of COs formed is 

 increased (Wolfers). 



240. Mixture of Flesh and Fat, 



or of Flesh and Carbohydrates. 



Since an amount of flesh equal to -^-g^ of the weight of the 

 body is required to nourish a dog, which is fed on a purely flesh 

 diet, if the necessary amount of fat or carbohydrates be added to 

 the diet, a quantity of flesh three or four times less is required. A 

 carbohydrate has a greater effect in diminishing the amount of urea 



