COMPOSITION OF THE URINE. 



417 



except in birds, in which Meissner has lately found it in considerable quantity. 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 sepa- 



FIG. 118. Crystals of uric acid obtained partly 

 by the solution and subsequent precipitation 

 of chemically pure acid, and partly by de- 

 composition of the urates by nitric or acetic 

 acid. (Funke.) 



FIG. 119. Urate of soda. (Funke.) 



rated by these organs from the blood. Meissner did not succeed in finding uric acid in 

 the muscular tissue, although 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 nitrogonized constituents of the body ; 

 and we should admit that as yet we are unable to designate the precise seat of their 

 formation or to follow out all the processes involved in their production. 



The daily excretion of uric acid, given in the table, is from six to nine grains ; which 

 is equal to from nine to fourteen grains of urates estimated as neutral urate of soda. Like 

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

 tions, which will be considered farther on. 



Hippuric Acid, Hippurates, and Lactates. The compounds of hippuric acid, which 

 are so abundant in the urine of the herbivora, are now known to be constant constitu- 

 ents of the 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 de- 

 tected in the blood of the ox by Verdeil and Dolfuss, and they 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. With regard to the exact mode of origin of the 

 hippurates, we have even less information than upon the origin of the other urinary con- 

 stituents 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. We must be content at present 

 simply to class the hippurates among the products of disassimilation, without attempting to 

 specify their exact mode of origin. The daily excretion of hippuric acid amounts to 

 about 7'5 grains, which is equivalent to about 8'7 grains of hippurate of soda. 



Hippuric acid itself, unlike uric acid, is quite soluble in water and in a mixture of 

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