AROMATIC SUBSTANCES. 605 
A very large number of tests for the presence of albumin and globulin in 
the urine have been described. We ran 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 - 00l' per cent, of albumin may be thus detected. The urinary 
nucleo-albumin 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. 
Werrocyanide 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 neittralisation, 
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 hippuric 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.r.), they are derived in part from tin- 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, Bel. ii. S. 256 ; Wolkow und 
Baumann, ibid, lS91,'Bd. xv. S. 228. 
