THE QUANTITY AND COMPOSITION OF THE URINE 339 



of the aromatic substances named phenolkresol and indoxyl combined with 

 sulphuric acid, as well as the compound named Brenz- or Pyro-catechin, 

 which is partly free and partly also combined with sulphuric acid. 



Pyro-catechin exposed to the air in an alkaline solution absorbs oxygen 

 and becomes brown, which is probably the cause of the darkening in 

 hue which the urine of the horse undergoes after expulsion from the 

 bladder. 



Veterinary Captain F. Smith, in a paper contained in the Proceedings 

 of the Royal Society gives the following instructive table showing the 

 mean composition of the urine of the horse for twenty-four hours at rest 

 and at work: — 



The difference in the size and breed of the animal probably accounts for 

 the great discrepancies in the analyses of the urine of the horse that have 

 been published. In some analyses made by Wessinger, who experimented 

 upon animals of Hungarian breed, it was found that the specific gravity 

 varied from U042 to U046, and that the amount of dry residue after 

 evaporation amounted to 6176-5404 grains per diem. The quantity of 

 chlorine varied within wide limits, but it may be taken at 400-500 grains. 

 The quantity of sulphuric acid was 262 grains. The quantity of nitrogen 

 varied in health from 994 grains to 1698 grains, the mean being 11 93 '5 

 grains. It is remarkable that the phosphates ingested with the food are 

 only eliminated in small quantity by the horse in the urine, whilst in 

 carnivora they are contained in large quantity. In the horse, the phos- 

 phates are discharged from the body by the bowels. The alkaline and 



