EXCRETION 445 



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, and the small amount of sulphur occurring in 

 less oxidized forms than sulphates in such compounds as the sul- 

 phocyanide, 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 (i H 5 KSO 4 ) , potassium-kresyl-sulphate 

 (C 7 H 7 KSO 4 ), potassium-indoxyl-sulphate (C H H ti NKSO 4 ), potassium- 

 skatoxyl-sulphate (C 9 H 8 NKSO 4 ), and two double sulphates of 

 potassium and pyrocatechin . The formation of potassium indoxyl 



~ ~ 



sulphate may be thus represented : Indol, CeH^ ^H OI * absorp- 

 tion from the intestine is changed into indoxyl, C*H 4 SS ' 



/OTT 



which + SO;/ OK (potassium hydrogen sulphate) yields 



(potassium indoxyl sulphate) + H 2 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 

 absorption 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 hi 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. 479). 



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

 mixing it with strong hydrochloric acid and distilling. These aro- 

 matic 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. 



The sulphur of the inorganic sulphates is the fraction of the total 

 sulphur which fluctuates in proportion to the total protein meta- 

 bolism. In this regard it follows the variations in the urea. It 

 represents ' exogenous ' metabolism. The neutral sulphur occupies 

 a position analogous to that of the kreatinin : the smaller the 

 amount of protein in the food, and the smaller therefore the total 

 protein decomposed, the larger is the fraction which the neutral 

 sulphur forms of the total sulphur. The neutral sulphur accordingly 

 represents endogenous metabolism. The ethereal sulphur takes 

 an intermediate position in this regard, but upon the whole it also 

 becomes a more prominent fraction of the total sulphur when the 

 food contains little or no protein. The ethereal sulphates are there- 

 fore not entirely derived from the putrefaction of protein. 



