202 EXCRETION. 



nitely determined, except in birds, where Meissner has lately 

 found it in considerable quantity. 1 The fact that the urates 

 exist in the liver, and in no other part except, perhaps, the 

 spleen has led Meissner to the opinion that this organ is the 

 principal seat of the formation of uric acid. However this 

 may be and the facts do not seem sufficiently definite to 

 lead to such an exclusive opinion it is certainly not formed 

 in the kidneys, but is simply separated by these organs from 

 the blood. Meissner did not succeed in finding uric acid in 

 the muscular tissue, though the specimens were taken from 

 the same animals in which he had found large quantities in 

 the liver. 



We have already discussed the theory of the change of 

 uric acid into urea. In the present state of our knowledge, 

 we must regard the urates, particularly the urate of soda, as 

 among the products of disassimilation of the nitrogenized 

 constituents of the body ; and we should admit that as yet 

 we are unable to designate the precise seat of their forma- 

 tion, or to follow out all the processes involved in their pro- 

 duction. 



The daily excretion of uric acid, given in the table, is 

 from six to nine grains ; which is equal to from nine to four- 

 teen grains of urates estimated as neutral urate of soda. 

 Like urea, the proportion of the urates in the urine is sub- 

 ject to certain physiological variations, which will be con- 

 sidered further on. 



IRppurates and Lactates. 



The compounds of hippuric acid (C 18 H 9 NO 6 ), which are 

 so abundant in the urine of the herbivora, are now known to 

 be constant constituents of the human urine. Robin states 

 that hippuric acid is always to be found in the urine of 

 children, but that it is sometimes absent temporarily in 

 the adult. 9 The presence of this acid in the normal human 



1 Loc. dt. 2 ROBIN, Lemons sur les humeurs, Paris, 1867, p. 678. 



