FATE OF THE ALBUMINOUS FOOD-CONSTITUENTS. 663 



uric acid by a process of decomposition of albuminous matters, differing 

 slightly from that which results in the production of urea. Sarkin and 

 xanthin, by progressive oxidation, might perhaps be converted into uric 

 acid, and, since they are usually found accompanying each other, will, 

 perhaps, indicate one source of uric acid. 



Sarkin, xanthin, and uric acid differ from each other only in one 

 atom of ox}rgen, thus : — 



Sarkin = C 5 H 4 N 4 0. 



Xanthin = C 5 H 4 N 4 0,. 



Uric acid = C 5 H 4 N 4 3 . 



As to where this conversion takes place we have no data to fall back 

 on, except that it does not occur in the kidneys, for the excision of the 

 kidneys or the ligation of the renal vessels leads to an accumulation of 

 uric acid in the economy. Of the different localities where uric acid 

 is especially met with the spleen occupies the first position. In the 

 spleen uric acid is constantly found in large quantities, even in the her- 

 bivora, whose urine is free from uric acid ; and conditions which lead to 

 an increased blood supply to the spleen, as in its enlargement in malarial 

 diseases, lead also to an increased excretion of uric acid. The spleen 

 ma^' therefore be looked upon both as the place of origin of uric acid in 

 the carnivora and of its destruction in the herbivora. 



In the herbivora uric acid is represented by hippuric acid, which 

 differs from uric acid in containing three atoms less of nitrogen, one 

 atom more of carbon, and five atoms more of hydrogen. 



Its formula is, therefore, C 6 H 9 N0 3 . 



In the herbivora the hippuric acid of the urine represents a peculiar 

 decomposition occurring in their food. Hippuric acid is a compound of 

 benzoic acid and glycoehol, and the administration of benzoic acid to 

 any animal, whether carnivorous or herbivorous, will result in the elimi- 

 nation of hippuric acid through the kidneys. 



This process of synthesis may be represented as follows : — 

 C 6 H 5 COOH + NH 2 CH 2 COOH = C 9 H 9 N0 3 +H 2 0. 



Hippuric acid has, therefore, its origin in the food. As long as the 

 herbivora are being suckled, or when fasting, it is absent from the urine, 

 but appears whenever vegetable matter is added in sufficient quantity to 

 the food. Certain forms of vegetable food are not, however, followed by 

 the elimination of hippuric acid. Hippuric acid is absent from the urine 

 of animals fed on peas, wheat, oats, or potatoes, but nearly all grasses 

 are, however, followed by its appearance in the urine. 



When benzoic acid is given to animals, hippuric acid is invariably 

 found in the urine, and an examination of the vegetable matters whose use 

 as food is followed by the formation of hippuric acid will nearly always 

 indicate the presence in such foods of benzoic acid or some allied body. 



