CARBOHYDRATES. 69 



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

 adding ammonia,when a bright purple color is produced (murexide 

 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 presence of acids, 



thus : 



Uric acid. Alloxan. Urea. 



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



C 2 H 3 2 



Hippuric Acid, C 9 H 9 NO. } , or C.H 5 O > N, 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 replaced by the radical benzoyl 

 (C 7 H 5 O). In the body it is combined 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 -f C 7 H 6 2 = C 2 H(C 7 H 5 O)(NH 2 )O.OH + H 2 O. 



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 pancreatic 

 digestion. It gives an odor to the faeces 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 (bleaching-lime) is 

 added, and the indigo which is formed can then be dissolved and 

 separated by agitation with chloroform. 



CLASS B. NON-NITROGENOUS. 

 Group V. CARBOHYDRATES. 



Carbohydrates (general formula, C m H 2n O n ) are bodies in which 

 the hydrogen and oxygen exist in the same proportion as in water, 



