COMPOSITION AND CHARACTERS OF URINE 1251 



It can be obtained in milk-white crystals (Fig. 518), which are only 

 slightly soluble in cold water, but easily soluble in alcohol ether, and 

 acetic acid. It is insoluble in petroleum, ether, and benzol. On 

 heating, it is broken up into benzoic acid and glycine. On heating 

 with concentrated nitric acid it forms nitro-benzol, which can be 

 recognised by its characteristic smell of bitter almonds. 



In order to extract it from the urine, the urine is made alkaline with sodium 

 carbonate, filtered, and the filtrate evaporated to a syrupy consistence. This 

 is then treated with alcohol, the alcohol evaporated, and the residue repeatedly 

 extracted with acetic ether. The acetic ether is collected, evaporated to dryness, 

 and the residue repeatedly extracted with petroleum ether to remove the benzoic 

 acid and fat. What is left behind is 

 hippuric acid, which can be purified by 

 recrystallisation from alcohol or ether. 



OTHER AROMATIC SUB- 

 STANCES. The chief of these is 

 the so-called ' urinary indican,' or 

 potassium-indoxyl-sulphate. This 

 is derived from the indol produced 

 in the intestines from the trypto- 

 phane contained in the proteins 

 of the food, the change being 

 effected by the influence of the 

 micro-organisms of putrefaction. 

 The amount of the conjugated 

 sulphates in the urine is thus an 

 index of the extent of putrefaction in the intestines. In dogs, 

 when the intestine has been disinfected by repeated doses of calomel, 

 the conjugated sulphates entirely disappear from the urine. Urinary 

 indican has the formula : 



H 



C 



FIG. 518. Hippuric acid. (FuNKE.) 



HC C COS0 9 OH 



HC C CH 



C 

 H 



N 

 H 



In addition to the tests for conjugated sulphates mentioned earlier, the 

 indoxyl-sulphate can be detected by various methods dependent on the forma* 

 tion of indigo blue. The urine is treated with an equal volume of concentrated 

 hydrochloric acid and several cubic centimetres of chloroform added. A con- 

 centrated solution of chloride of lime is now added drop by drop, shaking after 

 the addition of each drop. A blue colour is produced which is extracted by the 



