80 ORIGIN OF FAT IN 



urine of the horse and ox contains benzoic acid (with 

 14 equivalents of carbon) ; but as soon as the animal is 

 kept quiet in the stable, the urine contains hippuric acid 

 (with 18 equivalents of carbon). 



The flesh of wild animals is devoid of fat ; while 

 that of stall-fed animals is covered with that substance. 

 When the fattened animal is allowed to move more 

 freely in the air, or compelled to draw heavy burdens, 

 the fat again disappears. 



It is evident, therefore, that the formation of fat in 

 the animal body is the result of a want of due propor- 

 tion between the food taken into the stomach and the 

 oxygen absorbed by the lungs and the skin. 



A pig, when fed with highly nitrogenized food, be- 

 comes full of flesh ; when fed with potatoes (starch) it 

 acquires little flesh, but a thick layer of fat. The milk 

 of a cow, when stall fed, is very rich in butter, but in 

 the meadow is found to contain more caseine, and in 

 the same proportion less butter and sugar of milk. In 

 the human female, beer and farinaceous diet increase 

 the proportion of butter in the milk ; an animal diet 

 yields less milk, but it is richer in caseine. 



If we reflect, that in the entire class of carnivora, 

 the food of which contains no substance devoid of ni- 

 trogen except fat, the production of fat in the body is 

 utterly insignificant ; that even in these animals, as in 

 dogs and cats, it increases as soon as they live on a 

 mixed diet ; and that we can increase the formation of 

 fat in other domestic animals at pleasure, but only by 

 means of food containing no nitrogen ; we can hardly 



