EFFETE PRODUCTS. 77 



quantity in the urine of man. Traces have been found in many 

 tissues, in some of which large quantities accumulate as the result 

 of pathological processes (gout). It forms salts which are much 

 less soluble in cold than in hot water, and make the common 

 sediment in urine. The acid salts are less soluble than the neutral. 

 The common test for uric acid consists of slowly evaporating the 

 substance to dryness with a little nitric acid, and to the residue 

 adding ammonia, when a bright purple color is produced (mu- 

 rexide test). Uric acid is supposed to be a step in the production 

 of urea, which is one of the results of its oxidation in the pres- 

 ence of acids, thus : 



Uric acid. Alloxan. Urea. 



C 5 H 4 N 4 3 + H 2 + = C 4 H 2 N 2 4 -f CO(NH 2 ) 2 . 



C 2 H 3 2 ) 



Hippuric Acid, C 9 H 9 NO,, or C 7 H 5 \ N, 



H j 



occurs in considerable quantities in the urine of the horse and 

 herbivora generally. It is found but very sparingly in man's 

 urine, but it appears in large quantities after benzoic acid and 

 some other medicaments have been taken. In constitution it is 

 an amido-acetic acid in which one atom of the hydrogen is re- 

 placed by the radical benzoyl (C 7 H 5 O). In the body it is com- 

 bined with bases, and is formed out of benzoic acid and glycin 

 (amido-acetic acid), thus : 



Glycin. Benzoic acid. Hippuric acid. Water. 



C 2 H 2 (NH 2 )O.OH + C 7 H 6 2 = C 2 H(C 7 H 5 0)(NH 2 )O.OH + H 2 0. 



By heating or putrefaction it is resolved into these constituents. 



Indol, C 8 H 7 N, is produced in the intestinal canal by the putre- 

 factive changes brought about by septic agencies during pan- 

 creatic digestion. It gives an odor to the faces and a red color 

 with nitrous acid. 



Indican, a peculiar substance sometimes found in the urine and 

 sweat. With oxidizing agents it yields indigo blue. By this 

 fact it is easily recognized. An equal volume of hydrochloric 

 acid and a very small quantity of calcium hypochlorite (bleach- 

 ing lime) is added, and the indigo which is formed can then be 

 dissolved and separated by agitation with chloroform. 



