COMPOSITION OF THE UKINE. 413 



it replaces Uric Acid. Its composition and properties are very diffe- 

 rent from those of that substance. When pure, it forms long, transpa- 

 rent, four-sided prisms ; it is soluble in 400 parts of cold water, and 

 dissolves readily at a boiling heat ; and it has a strong acid reaction, 

 with a bitterish taste. It is composed of 18 Carbon, 8 Hydrogen, 1 

 Nitrogen, and 5 Oxygen, with 1 equiv. of Water. When exposed to a 

 high temperature, or subjected to the putrefactive process, it is partly 

 converted into Benzoic acid ; and it is on the presence of the latter in 

 putrefied Human Urine, that the belief in the existence of Hippuric 

 acid in the same fluid when fresh, is chiefly grounded. It is a curious 

 fact, that the administration of Benzoic acid causes the appearance of 

 a large additional quantity of Hippuric acid in the Urine, so that its 

 presence is then sufficiently evident ; and this 'seems to be due to the 

 union of the benzoic acid within the system, either with glycocoll ( 176), 

 or with the elements which would have formed it ; for one equivalent of 

 benzoic acid, added to one of glycocoll, gives the precise equivalent of 

 hippuric acid. It does not appear that, as once asserted, the adminis- 

 tration of benzoic acid diminishes the quantity of uric acid normally 

 present in the urine ; but it seems to bring down the excess, where such 

 exists, to about the normal quantity ; and it may thus be employed with 

 advantage in cases of uric acid gravel. 



735. Much discussion has taken place, as to the normal presence of 

 Lactic acid in the urine ; and the question cannot even now be regarded 

 as completely determined. It is certain that the peculiar crystalline 

 compound, procurable by treating the urine with zinc in solution, is not 

 as was formerly maintained, a lactate of zinc ; but that its composition 

 is altogether different, as will be presently explained. But, on the 

 other hand, it appears from the researches of Lehmann and others, 

 that lactic acid is usually present in small quantity in healthy urine ; 

 and that its quantity may be increased under such conditions, as either 

 tend to augment the quantity of lactic acid in the blood, or to obstruct 

 its elimination by the respiratory process. Thus an excess of farina- 

 ceous food, which furnishes sugar and lactic acid faster than they can 

 be thrown off as carbonic acid and water ; or an excess of exertion of 

 the muscles, of whose disintegration lactic acid appears to be one of 

 the results ; or pulmonary diseases, which interfere with the normal 

 aeration of the blood ; all favour the appearance of lactic acid in the 

 urine. It seems to be constant in herbivorous animals, and in patients 

 suffering under chronic bronchitis, pulmonary emphysema, and similar 

 disorders. The urine of Man, more uniformly contains, however, two 

 substances termed Kreatine and Kreatinine ; which seem to be the 

 result of the degeneration of the muscles, as they may be obtained from 

 the juice of raw flesh. The former of these, which is found in largest 

 amount, is a neutral substance, crystallizing in long prisms, sparingly 

 soluble in cold water, but dissolving readily in warm. By the action 

 of strong acids, kreatine may be readily converted into kreatinine, 

 which only differs from it in composition by containing two proportion- 

 als less of the elements of water, but is a substance of very different 

 chemical relations, having a strong alkaline reaction, and serving as a 

 powerful organic base to acids. When long boiled withs caustic baryta, 



