AROMATIC SUBSTANCES. 605 



A very large number of tests for the presence of albumin and globulin in 

 the urine have been described. We can here refer to two only. 



Heller's test. A small quantity of strong nitric acid is placed in a test 

 tube, and the urine is allowed to flow gently down the side of the tube so that 

 it floats upon the surface of the acid without mixing with it. If coagulable 

 proteids are present, a dense white ring forms at the junction of the liquids. 

 As little as '002 per cent, of albumin may be thus detected. The urinary 

 nucleo-albumm may react to this test if in sufficient quantity, but the ring 

 formed is less dense, and more apt to be formed at some little distance from the 

 acid. 



Ferrocyanide test. -A-solution of potassic ferrocyanide is first added to the 

 urine, and the mixture made acid with acetic acid, when the albumin and 

 globulin are precipitated as a flocculent cloud. If the salt be added before the 

 acid, nucleo-proteid is not precipitated. 



To separate serum globulin from albumin, the urine is, after neutralisation, 

 saturated with magnesium sulphate, which precipitates the former. The 

 precipitate may contain certain of the salts of the urine, and heteroalbumose 

 if present. The proportion of globulin to albumin may vary greatly, and may 

 be quite different from that present in the blood. 



To detect peptones, the urine is saturated with sulphate of ammonium, and, 

 after standing, filtered ; the biuret test may now be applied to the filtrate, a 

 large excess of caustic alkali being used. The ammonium sulphate precipitate 

 contains (in addition to ammonium urate) all other proteids present and also 

 the urinary mucin. If this precipitate be allowed to stand under alcohol for 

 some days, the proteoses are obtained in solution when it is extracted with 

 water. The presence of urates must be borne in mind when the ammonium- 

 sulphate precipitate is being dealt with, as these yield a coloration with certain 

 proteid tests ; and again, may lead to error if ordinary mucin is to be identified 

 by its yield of a reducing body on boiling with acids, for uric acid itself 

 reduces copper solutions. 



AROMATIC SUBSTANCES. 



In addition to hippiiric acid, which, owing to its importance as a 

 nitrogenous constituent, we have treated specially, the urine contains 

 other substances belonging to the aromatic group ; that is to say, 

 substances the molecular structure of which contains the benzene 

 nucleus. Under normal circumstances each one of these is present in 

 very small amount, but collectively they are of importance. For our 

 knowledge of their chemistry in the urine we are largely indebted to 

 the initiative work of Baumann. 



Like hippuric acid (q.v.), they are derived in part from the aromatic 

 constituents of the food, and they are all increased by a vegetable diet ; 

 but also, like hippuric acid, they partly arise from the breakdown of 

 proteids. In their derivation from the latter it is possible that tyrosine 

 in the bowel is an intermediate stage, as many of them are greatly 

 increased when that substance is given by the mouth. 1 We cannot deal 

 with these substances in great detail, but the characteristic types 

 of compounds in which the aromatic nucleus is found in the urine 

 should be noted. They comprise, mainly, simple hydroxyl- substitution 

 products of benzene, and carboxyacids related to these. We shall also 

 consider in this section urinary indol and skatol, which are nitrogenous 

 aromatic compounds. Most of the substances to be dealt with are 



1 Brieger, Ztschr. f. physiol. Chem., Strassburg, 1878, Bd. ii. S. 256 ; Wolkow imd 

 Baumami, ibid, 1891,' Bd. xv. S. 228. 



