URIC ACID. 459 



The condition in which, uric acid exists in solution in the 

 urine has formed the subject of some discussion,, because 

 of its difficult solubility in water. 



According to Liebig the uric acid exists as urate of soda, 

 produced, he supposes, by the uric acid, as soon as it is 

 formed, combining with part of the base of the alkaline 

 phosphate of soda of the blood. Hippuric acid, which 

 exists in human urine also, he believes, acts upon the 

 alkaline phosphate in the same way, and increases still 

 more the quantity of acid phosphate, on the presence of 

 which it is probable that a part of the natural acidity of 

 the urine depends. It is scarcely possible to say whether 

 the union of uric acid with the base soda and probably 

 ammonia, takes place in the blood, or in the act of secre- 

 tion in the kidney : the latter is the more probable 

 opinion ; but the quantity of either uric acid or urates in 

 the blood is probably too small to allow of this question 

 being solved. 



The source of uric acid is probably in the disintegrated 

 elements of albuminous tissues. The relation which uric 

 acid and urea bear to each other is, however, still obscure. 

 The fac.t that they often exist together in the same urine, 

 makes it seem probable that they have different origins or 

 different offices to perform : but the entire replacement of 

 either by the other, as of urea by uric acid in the urine of 

 birds, serpents, and many insects, and of uric acid by urea, 

 in the urine of the feline tribe of Mammalia, shows that 

 each alone may discharge all the important functions of 

 the two. 



Owing to its existence in combination in healthy urine, 

 uric acid for examination must generally be precipitated 

 from its bases by a stronger acid. Frequently, however, 

 when excreted in excess, it is deposited in a crystalline 

 form (fig. 120), mixed with large quantities of urate of 

 ammonia or soda (fig. 123). In such cases it may be 

 procured for microscopic examination, by gently warming 



