478 EXCRETION 



fermentation. In some pathological urines they come down when the 

 carbon dioxide is driven off by heating; a precipitate of this sort differs 

 from heat-coagulated albumin in being readily soluble in acids (Practical 

 Exercises, p. 516). A small amount of phosphorus may appear in the 

 urine in a less oxidized form than phosphoric acid. 



Sulphuric Acid. This is only to a slight extent derived from ready- 

 formed sulphates in the food. The greater part of it is formed by 

 oxidation of the sulphur of proteins. About nine-tenths of the sulphur 

 in normal urine is present as inorganic sulphates, mainly those of 

 potassium and sodium. Of the other tenth, a portion is represented 

 by ethereal sulphates, and the remainder by the so-called ' neutral ' 

 sulphur, including the sulphur associated with the pigment urochrome. 

 A small amount of sulphur occurs in less oxidized forms than sul- 

 phates in such compounds as the sulphocyanide, which is probably, 

 in part but not entirely, derived from that of the saliva, and ethyl 

 sulphide, a substance with a penetrating odour, which appears to be a 

 constant constituent of dog's urine (Abel). 



Thiosulphuric acid (H 2 S 2 O 3 ) occurs almost constantly in cat's urine, 

 often in dog's. It is not free, but combined with bases. 



The ethereal sulphates are compounds in which the sulphuric acid is 

 united with aromatic bodies (indol, phenol, etc.). Such are potassium- 

 phenyl-sulphate (C 6 H 5 KSO 4 ), potassium-kresyl-sulphate (C 7 H 7 KSO 4 ), 

 potassium-indoxyl-sulphate (C 8 H C NKSO 4 ) , potassium-skatoxyl-sulphate 

 (C 9 H 8 NKSp 4 ), and two double sulphates of potassium and pyrocatechin. 

 The formation of potassium indoyxl sulphate may be thus represented : 



Indol, QH 4 < JTTT' on a bsorption from the intestine is changed into 



indoxyl, C 6 H 4 /^ H ' CH ' which + SO 2 / (potassium hydrogen 



sulphate) yields SOaQ (potassium indoxyl sulphate) + H a O. 



The ' pairing ' of these aromatic bodies with sulphuric acid renders 

 them innocuous to the organism. Most of the compounds are present 

 in greater amount in the urine of the horse than in the normal urine of 

 man. But in disease the quantity of indican in the latter may be much 

 increased ; and to a certain extent it must be looked upon as an index 

 of the intensity of putrefactive processes in the intestine and of absorp- 

 tion from it. Munk made the observation that in the urine of a starving 

 dog the phenol-forming substances are absent, while in the urine of a 

 starving man they are present in abnormally large amount. The 

 indigo-forming substances (indican), on the other hand, are in hunger 

 excreted in considerable quantity by the dog, and not at all by man 

 (Practical Exercises, p. 5 10) . According to Folin, the indoxyl potassium 

 sulphate or indican of the urine is not to any appreciable extent related 

 to protein metabolism, but for the most part to the putrefaction of 

 protein in the intestine. The indoxyl-potassium sulphate taken by itself 

 may therefore afford a rough index of the intensity of the intestinal 

 putrefactive processes. On the other hand, the total ethereal sulphuric 

 acid cannot be taken as an index of the extent of the putrefaction, for, 

 although absolutely diminished, it is increased relatively to the total 

 excretion of sulphur on a diet poor in protein, or even protein-free 

 (see tables on p. 471). 



Phenol and kresol can easily be obtained from horse's urine by 

 mixing it with strong hydrochloric acid and distilling. Thes- aromatic 

 bodies pass over in the distillate. Pyrocatechin remains behind, and 

 can be extracted by ether. It gives a green colour with ferric chloride, 

 which becomes violet on the addition of sodium carbonate. 



