EXCHANGE OF MATEEIAL 



31 



nitrogenous food-stuffs have the same effect when no other food 

 is given. 



On a diet consisting only of fat there is no saving in the 

 consumption of the protein of the organism, since the quantity 

 of nitrogen contained in the urine remains the same, and even 

 increases if too large a quantity of fat be given to the animal 

 after a period of fasting. The consumption of fat steadily 

 increases, but the whole of the fat eaten is not always burnt, 

 and part of the fat stored up in the organism is spared, which 

 fact explains why death from inanition does not take place so 

 quickly as when the fast is absolute. These facts are clearly 

 proved by the researches carried out by Frerichs and Voit, as will 

 be seen by the following tables : 



Likewise a diet consisting exclusively of saccharides, starch, 

 cane sugar, grape sugar, milk sugar, does not diminish the 

 consumption of nitrogen below the amount which obtained 

 previously when the animal was in a fasting condition : it remains 

 unchanged, and does not increase as sometimes happens in the 

 case of a diet of fat when the quantity given is increased. 

 Inanition and death cannot be prevented if the diet consists 

 wholly of carbohydrates, though they may be postponed longer 

 than in the case of an absolute fast (Frerichs). The nutritive 

 value of fats and saccharides and the different way in which they 

 act upon metabolism can be deduced from the results of the 

 experiments in which fats or saccharides are added to the meat or 

 general protein diet. 



If fat be added to the diet of meat, the consumption of protein 

 does not fall, when compared with that seen previously in a fasting 

 condition ; if, however, this diet be continued for a number of days, 

 the animal will accumulate fat, and in proportion to its increase 

 of fat will be the diminution in the quantity of flesh consumed. 

 Thus fat added to the protein diet saves the consumption of flesh 

 indirectly, that is, by fattening the animal. When carbohydrates 



