THE URINE 



329 



being converted into urea. When, as occurs in herbivora, there 

 is already an excess of alkali in the diet, a sufficiency of bases is 

 present to neutralise the acid, so that the normal conversion 

 of ammonia into urea continues, and no ammonia appears in 

 the urine. The evidence which bears on this is afforded by the 

 injection of acids into the circulation. This, in a dog, does 

 not alter the reaction of the blood, for ammonia is produced 

 in sufficient quantities to neutralise it. In herbivora, on the 

 other hand, the ready supply of ammonia is not available, the 

 store of vegetable alkaline salts is soon used up, and the animal 

 suffers more acutely, and is more readily killed by acid poisoning 

 than is the case with carnivora. It is rather a difficult matter 

 to increase the acidity of an acid urine. Mineral acids effect 

 it, but if the acid be pushed 

 too far ammonia is split off 

 from the protein in order to 

 counteract toxic results. On 

 the other hand, it is very 

 easy to increase the alka- 

 linity of an alkaline urine. 

 It may be well to explain 

 that the poisoning which 

 occurs from acidosis is due 

 to the reduced carrying 

 power of the blood for car- 

 bon dioxide. In conse- 

 quence, this substance is 

 retained in the tissues with 

 fatal results. The adminis- 

 tration of ammonium car- 

 bonate by the mouth will not prevent this condition, since 

 it appears in the urine as urea. 



Free ammonia exists in the urine of the horse. It may be 

 owing to ammoniacal fermentation in the bladder, but it is quite 

 certain that perfectly fresh urine may give marked evidence 

 of the presence of free ammonia. On standing a short time 

 outside the body, especially in summer weather, the urea decom- 

 poses, as previously mentioned (p. 322) , and ammonium carbonate 

 is largely formed. 



Sulphuric Acid. — The sulphates in the urine, especially that 

 of herbivora, and more particularly the horse, are an excretion 

 of considerable importance. In all animals three varieties of 

 sulphur-containing substances are found — viz. : 



Inorganic sulphur. 

 Neutral sulphur. 

 Ethereal sulphates. 



Fig. ioi. — Crystals of Benzoic Acid. 



