330 A MANUAL OF VETERINARY PHYSIOLOGY 



And from this it might be supposed that the sulphates taken 

 into the body with the food represent something considerable. 

 As a matter of fact, the sulphates in food exist only in traces, 

 and the above compounds are really derived from the oxidation 

 of the sulphur of protein substances undergoing disintegration. 



The Inorganic Sulphur is believed to be derived from the 

 katabolism of proteins in the intestinal canal, or, at any rate, 

 from the destruction of protein substances not yet forming part 

 of the body ; hence it is spoken of as the exogenous portion, as 

 in the case of urea and uric acid. The quantity of sulphates 

 excreted in this form varies considerably, as it depends upon 

 the amount of protein in the diet ; they pass from the body as 

 salts of sodium and potassium. 



The Neutral Sulphur is furnished from the actual proteins of 

 the tissues ; it is not liable to great variations, and the amount 

 for the individual may even be constant. Included with it is 

 the sulphur of the pigment urochrome and of other minor 

 sulphur compounds, such as ethyl sulphide, found in the urine 

 of the dog, and sulphocyanic acid, said to be a constant con- 

 stituent of the urine of herbivora. 



Coming between the above is a third variety of sulphur com- 

 pounds — the Ethereal Sulphates, which are furnished by the tissue 

 proteins, but also, in part, from non-protein substances. This 

 is a very characteristic group in the urine of the herbivora, 

 especially that of the horse, for they form compounds with such 

 poisonous substances as indol, phenol, skatol, kresol, which 

 are produced in the intestinal canal of the animal, both in conse- 

 quence of the disintegration of protein substances, the result of 

 bacterial putrefaction, but also from certain benzene constituents 

 in vegetable food. These aromatic and highly poisonous bodies 

 mentioned above are either excreted unabsorbed from the 

 intestinal canal, or if absorbed, unite in the blood-stream with an 

 alkaline sulphate to form conjugated or ethereal sulphates, and 

 in this way are rendered innocuous. 



The compounds formed by sulphuric acid with the aromatic 

 bodies are — 



Potassium phenyl sulphate. 

 Potassium kresyl sulphate. 

 Potassium indoxyl sulphate. 

 Potassium skatoxyl sulphate. 



To the compound potassium indoxyl sulphate the name 

 indican has l^een, given. This substance on oxidation yields 

 indigo blue, which is comparatively abundant in the urine of 

 the horse. Phenyl-sulphuric acid in the presence of air under- 

 goes oxidation, and yields pyrocatechin, which gives the brown 



