81 



Oxalate of lime, like carbonate of lime, is derived from the burning 

 nj) of the carbonaceous matter of the food in the system, one impor- 

 tant factor being the less perfect oxidation of the carbon. Indeed, 

 Fiirstenberg and Schmidt have demonstrated on man, horse, ox, and 

 rabbit, that under the full play of the breathing (oxidizing) forces, 

 oxalic, like other organic acids, is resolved into carbonic acid. In 

 keei)ing with this is the observation of Lehmann that in all cases in 

 which man suffered from interference with the breathing, oxalate of 

 lime appeared in the urine. An excess of oxalate of lime in the urine 

 may, however, claim a different origin. Uric and hippuric acids are 

 found in the urine of carnivora and herbivora, respectivel}^ as the 

 result of the healthy wear (disassimilation) of nitrogenous tissues. 

 But if these products are fully oxidized they are thrown out in the 

 form of the more soluble urea rather than as these acids. When uric 

 acid out of the body is treated with peroxide of lead it is resolved into 

 urea, allantoine, and oxalic acid, and AYoehler and Frerrichs found 

 that the administration of uric acid not onlj^ increased the excretion 

 of urea, but also of oxalic acid. It may therefore be inferred that 

 oxalic acid is not produced from the carbonaceous food alone, but also 

 from the disintegration of the nitrogenous tissues of the body. An 

 important element of its j)roduction is, however, the imi^erfect pev- 

 formance 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 generally, pota- 

 toes, etc.). 



Carbonate of magnesia, another almost constant ingredient of the 

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

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

 becoming oxidized into carbon dioxide, which unites with the mag- 

 nesia derived from the food. 



The phosphates of lime and magnesia are not abundant in urinary 

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

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

 specially rich in phosphorus (wheat bran, beans, pease, 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, hoAvever, 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, j)hosphate 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. 



