96 BUREAU OF ANIMAL INDUSTRY. 



element of its production is, however, the imperfect performance of 

 the breathing functions, and hence it is liable to result from diseases 

 of the chest (heaves, chronic bronchitis, etc.). This is above all likely 

 to prove the case if the subject is fed to excess on highly carbonaceous 

 foods (grass and green food general!}', potatoes, etc.). 



Carbonate of magnesia, another almost constant ingredient of the 

 urinar}^ calculi of the horse, is formed in the same waj' as the carbon- 

 ate of lime — from the excess of carbonaceous food (organic acids) 

 becoming oxidized into carbon dioxide, which unites w ith the magnesia 

 derived from the food. 



The phosphates of lime and magnesia are not abundant in urinary 

 calculi of the horse, the phosphates being onl}^ present to excess in 

 the urine in two conditions — (a) when the ration is excessive and spe- 

 cially rich in phosphorus (wheat bran, beans, pease, vetches, rape 

 cake, oil cake, cotton-seed cake); and (h) when, through the morbid 

 destructive changes in the living tissues, and especiallj^ of the bones, 

 a great amount of phosphorus is given off as a waste product. Under 

 these conditions, however, the phosphates may contribute to the for- 

 mation of calculi, and this is, above all, likely if the urine is retained 

 in the bladder until it has undergone decomposition and given off 

 ammonia. The ammonia at once unites with the phosphate of mag- 

 nesia to form a double salt — phosphate of ammonia and magnesia— 

 which, being insoluble, is at once precipitated. The precipitation of 

 this salt is, however, rare in the urine of the horse, though much 

 more frequent in that of man and sheep. 



These are the chief mineral constituents of the urine which form 

 ingredients in the horse's calculi, for though iron and manganese are 

 usually present it is onl}^ in minute quantities. 



The excess of mineral matters in a specimen of urine unquestion- 

 ably contributes to the formation of calculi, just as a solution of such 

 matters out of the bod}^ is increasingly disposed to throw them down in 

 the form of crystals as it becomes more concentrated and approaches 

 nearer to the condition of saturation. Hence, in considering the 

 causes of calculi we can not ignore the factor of an excessive ration, 

 rich in mineral matters and in carbonaceous matters (the source of 

 carbonates and much of the oxalates), nor can we overlook the con- 

 centration of the urine that comes from dry food and privation of 

 water, or from the existence of fever which causes suspension of the 

 secretion of water. In these cases, at least the usual amount of solids 

 is thrown off by the kidneys, and as the water is diminished there 

 is danger of its approaching the point of supersaturation, when the 

 dissolved solids must necessarll}^ be thrown down. Hence, calculi 

 are more common in stabled horses fed on dry grain and hay, in those 

 denied a sufEciency of water or that have water supplied irregularlv, 

 in those subjected to profuse perspiration (as in suiumer), and in 



