344 EXCRETION 



potassium, calcium and magnesium. Of these combinations, the sodium 

 urate and ammonium urate are by far the most important, and they con- 

 stitute a great proportion of the urates, potassium, calcium and magne- 

 sium urates existing only in minute traces. Sodium urate is much more 

 abundant than ammonium urate. The union of uric acid with the bases 

 is very feeble. If from any cause the urine becomes excessively acid 

 after its emission, a deposit of uric acid is likely to occur. The addi- 

 tion of a very small quantity of almost any acid is sufficient to decom- 

 pose the urates, when the uric acid appears after a few hours, in a 

 crystalline form. 



Uric acid, probably in combination with bases, is always found in the 

 substance of the liver in large quantity. The urates also exist in the 

 blood in small quantity and pass ready-formed' into the urine. The fact 

 that the urates exist in the liver has led to the opinion that this organ is 

 the principal seat of the formation of uric acid (Meissner). However 

 this may be, uric acid certainly is 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, although the speci- 

 mens were taken from animals in which he had found large quantities in 

 the liver. The urates, particularly sodium urate, are products of katabo- 

 lism of the proteid constituents of the body. 



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

 grains (0.39 to 0.58 gram), the equivalent of nine to fourteen grains 

 (0.58 to 0.9 gram) of urates estimated as neutral sodium urate. Like 

 urea,, the proportion of urates in the urine is subject to certain physio- 

 logical variations. 



Hippuric Acid y Hipptirates and Lactates. The compounds of hip- 

 puric acid (C 9 H 9 NO 3 ), which are so abundant in the urine of the her- 

 bivora, are now known to be constant constituents of human urine. 

 Hippuric acid is always to be found in the urine of children, but it is 

 sometimes absent temporarily in the adult. The hippurates have been 

 detected in the blood of the ox and have since been found in the 

 blood of the human subject. There can be scarcely any doubt that 

 they pass ready-formed from the blood into the urine. As to the 

 exact mode of origin of the hippurates, there is even less information 

 than in regard to the origin of the other urinary constituents already 

 considered. Experiments have shown that the proportion of hippuric 

 acid in the urine is greatest after taking vegetable food ; but it is found 

 after a purely animal diet, and probably it also exists during fasting. 

 The daily excretion of hippuric acid is about 7.5 grains (0.486 gram), 

 which is equivalent to about 8.7 grains (0.566 gram) of sodium hip- 

 p urate. 



