112 CRYSTALLIZABLE NITROGENOUS MATTERS. 



absent, or nearly so, in that of the carnivorous animals. In human 

 urine, under an ordinary mixed diet, it is constantly present, amount- 

 ing to about 0.35 gramme per day, or about one-half the quantity of 

 uric acid. It increases, however, perceptibly under a vegetable diet, 

 and diminishes or disappears altogether under the exclusive use of ani- 

 mal food. It thus alternates in quantity, under these circumstances, 

 with uric acid. In the urine of the horse, which normally contains 

 hippuric acid, after continued abstinence from food, this substance 

 ceases to appear, and uric acid takes its place. Herbivorous animals, 

 when deprived of food, are placed in the condition of carnivora, since 

 the ingredients of the urine must then be derived from the metamor- 

 phosis of their own substance. In the calf, while living upon the milk 

 of its dam, the urine contains uric acid ; after the animal is weaned and 

 begins to live upon vegetable food, the uric acid disappears, and the 

 urine contains salts of hippuric acid. 



