URINE AND ITS CONSTITUENTS. 721 



secreted by the members of some families, and seems to be without 

 pathological significance, except that it may be deposited in the 

 bladder and form calculi. 



Cystine is insoluble in water, alcohol, and ether, but is readily soluble in 

 ammonia- water ; boiled with solution of sodium hydroxide a sulphide of sodium 

 is formed which stains silver black. Cystine crystallizes in characteristic regu- 

 lar six-sided tablets, and is best recognized microscopically in the precipitate 

 formed by adding acetic acid to urine. Inorganic sulphates of sodium, potas- 

 sium, and magnesium are present, but possess no great interest. 



Ethereal sulphates. As the conjugated substances (phenol, para- 

 cresol, skatole, indole, etc.) are formed in the intestine as putrefac- 

 tion products of the proteins, and are conjugated (in the liver) merely 

 for excretion, the resulting organic sulphates are increased whenever 

 the intestinal putrefaction is increased. The estimation of these 

 bodies as sulphates is, however, seldom carried out, as the increase is 

 important only when it is marked, and it is simpler to show an in- 

 crease of the non-sulphate portion. The indican tests are commonly 

 made use of in this connection. 



Indican, indoxyl-sulphuric add, C 8 H 7 NSO 4 , 



/ NH \ 



C 6 H <^ ^CH This compound is not identical with the 



X C^_O SO 2 .OH. 



indican found in woad and a few other plants. The vegetable indican 

 is a glucoside, C 26 H 31 NO 7 , yielding by fermentation, among other 

 products, dextrose and indigo-blue, C 16 H 10 N 2 O 2 . The latter is iden- 

 tical with the indigo obtained from indoxyl-sulphuric acid, which 

 decomposes into sulphuric acid (or a salt of it), and indoxyl, which 

 latter, by oxidation, yields indigo, thus : 



C 8 H 6 KNSO, + H,0 = C 8 H 7 NO + KHSO 4 



Potassium Indoxyl. 



indoxy 1-sul ph ate. 



2(C 8 H 7 NO) + 2O = C 16 H 10 N 2 2 -f 2HjO 

 Iiidoxyl. Indigo. 



The source and formation of indican in the body have been men- 

 tioned. In urine it occurs normally to the extent of 0.002 per cent., 

 while pathologically the quantity may be much greater. Indican is 

 pale yellow, but is easily converted into indigo-blue, and it is this 

 property which is used for its detection. 



Tests for indican. 



1. Mix equal volumes of urine and strong hydrochloric acid ; then 

 add drop by drop a solution of bleaching-powder until the maximum 



Afi 



