90 



CHEMICAL COMPOSITION OF THE BODY. 



be precipitated unaltered on the addition of water. On subjecting it to a 

 high temperature, it decomposes and yields urea and cyanuric acid ; with 

 oxidizing agents, as ozone and peroxide of lead, it gives allantoin, urea, 

 oxalic and carbonic acids. When acted on by nitric acid, and evaporated 

 to dryness, the residue slightly moistened with ammonia, assumes a beauti- 

 ful purple tint from the formation of murexide. Uric acid is found in the 

 urine, the blood, the juice of flesh, and in glandular structures, in all of 

 which it probably exists in the condition of urate of soda. It proceeds 

 from the decomposition of the albuminous compounds, and contains 33 per 

 cent, of nitrogen. The proportion of N to C is as 1 : 2j. 



FIG. 48. 



FIG. 4!>. 



Uric acid. 



Hippuric acid. 



HIPPITRIC ACID, C 9 H 9 NO 3 , is one of the constituents of human urine, 

 though, like the last-named acid, it exists only in small quantity. It is 

 always more abundant in the urine of the herbivorous than in that of car- 

 nivorous animals. It may be obtained from the urine of the cow or horse 

 by simple addition of hydrochloric acid, when it crystallizes out; by re- 

 solution and filtration through animal charcoal, it appears in the form of 

 beautiful, transparent, colorless, four-sided prisms, which belong to the 

 rhombic system. They are soluble with difficulty in cold water and in ether, 

 but more easily in hot water and in alcohol. When benzoic acid is ingested, 

 it is eliminated from the body as hippuric acid a change that probably 

 takes place at the liver, since beuzoic forms hippuric acid by taking up 

 glycin and giving off ten equivalents of water, and it is remarkable that all 

 the herbivora secrete bile which is rich in glycin. Hippuric acid also ap- 

 pears in the urine after the iugestion of bitter-almond oil, cinnamic acid, 

 chinic acid, and toluol into the stomach. Meissner and Shephard 1 have 

 shown that the hippuric acid of the herbivora is directly dependent on the 

 nature of the aliment, since on feeding them with non-albuminous com- 

 pounds fat, sugar, and starch they ceased to pass this acid in the urine, 

 whilst it reappeared when they were fed on hay, straw, or clover. They be- 

 lieve this to be due to the presence in the latter of a body belonging to the 

 benzole atomic group, and by a process of exclusion, that it was the thick- 

 ened and infiltrated cell-walls of the epidermis cells which furnished the 

 primary substance that by conversion yielded the acid. Thudichunr has 

 recently described another acid, the Kryptophanic, to the presence of which 

 he attributes the normal acid reaction of the urine. It is amorphous, re- 



1 Untersuchungen iiberd. EiUstelien der Hippursaure, im Thier. Organismus, 1866. 

 3 Central blutt, 1870, p. 195. 



