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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 sub- 

 ject is fed to excess on highly carbonaceous foods (grass and green food 

 generally, potatoes, etc.). 



Carbonate of magnesia, another almost constant ingredient of the 

 urinary calculi of the horse, is formed in the same way as the carbonate 

 of lime, from the excess of carbonaceous food (organic acids), becoming 

 oxidized into carbon dioxide, which unites with the magnesia derived 

 from the food. 



The phosphates of lime and magnesia are not abundant in urinary 

 calculi of the horse, the phosphates being only present to excess in the 

 urine in two conditions; (a) when the ration is excessive and specially 

 rich in phosphorus (wheat bran, beans, peas, vetches, rape cake, oil 

 cake, cotton-seed cake); and {b) when through the morbid destructive 

 changes in the living tissues, and especially 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 formation of 

 calculi, and this is, above all, likely if the urine is retained in the blad- 

 der until it has undergone decomposition and given off ammonia. The 

 ammonia at once unites with the phosphate of magnesia to form a 

 double salt, phosphate of ammonia and magnesia, which, being insolu- 

 ble, 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 in- 

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

 usually present it is only in minute quantities. 



The excess of mineral matters in a specimen of urine unquestionably 

 contributes to the formation of calculi, just as solution of such matters 

 out of the body 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 mat- 

 ters and in carbonaceous matters (the source of carbonates and much 

 of the oxalates), uor cau we overlook the concentration 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 are thrown oft' by the kid- 

 neys, and as tht. water is diminished there is danger of its approaching 

 the point of supersaturation, when the dissolved solids must necessa- 

 rily be thrown down. Hence, calculi are more common in stabled 

 horses fed on dry grain and hay, in those denied a sufficiency of water 

 or that have water supplied irregularly, in those subjected to profuse 

 perspiration (as in summer), and in those suffering from a watery 

 diarrhea. On the whole, calculi are most commonly found in winter, 

 because the horses are then on dry feeding, but such dry feeding is 



