1120 PHYSIOLOGY 



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. 



AMINO- ACIDS. According to Levene and van Slyke amino-acids are 

 always present in the urine, and contribute about 1 -5 per cent, of the total 

 nitrogen. 



OTHER AROMATIC SUBSTANCES. 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 tryptophane 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 calo- 

 mel, the conjugated sulphates entirely 

 disappear from the urine. Urinary 

 indican has the formula : 



HC 

 HC 



CH 



FIG. 520. Hippuric acid. (FTJNKE.) 



C N 

 H H 



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

 sulphate can be detected by various methods dependent on the formation of indigo blue. 

 The urine is treated with an equal volume of concentrated hydrochloric acid and 

 several cubic centimetres of chloroform added. A 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 chloroform. It is important not to add too much 

 chloride of lime, as otherwise the blue colour first produced will be destroyed by further 

 oxidation. 



THE URINARY PIGMENTS. Normal urine gives no definite absorption 

 bands. It owes its colour to the presence of a yellow pigment, urochrome. 

 In order to separate urochrome from urine, the urine is saturated with 

 crystals of ammonium sulphate and filtered. The filtrate, which still 

 contains nearly all the colour of the urine, is shaken up with alcohol, which 

 withdraws the greater part of the colouring-matter. On concentrating the 

 alcoholic solution and pouring it into an equal volume of ether, an amor- 

 phous brown precipitate falls, which is the urochrome. Urochrome, on 

 treatment with^aldehyde, yields a pigment closely similar to urobilin. On 

 the other hand, urobilin, treated with potassium permanganate, is converted 

 into a substance practically identical with urochrome. Urochrome must 

 therefore be derived from the same source as urobilin. 



