DISEASES OF THE XJRINAKY ORGANS. 155 



In keeping 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, respectively, 

 as the result of the healthy wear (disassimilation) of nitrogenous tis- 

 sues. If these products are fully oxidized, however, 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 peroxid of lead it is 

 resolved into urea, allantoin, and oxalic acid, and Woehler and Frer- 

 richs found that the administration of uric acid not only increased 

 the excretion of urea but also of oxalic acid. It may therefore be 

 inferred that oxalic acid is not produced from the carbonaceous feed 

 aione but also from the disintegration of the nitrogenous tissues of 

 the body. An important 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, liable to prove the case if the subject is fed 

 to excess on highly carbonaceous feeds (grass and green feed gener- 

 ally, potatoes, etc.). 



Carbonate of magnesia, another almost constant ingredient of the 

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

 nate of lime — from the excess of carbonaceous feed (organic acids) 

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

 nesia derived from the feed. 



The phosphates of lime and magnesia are not abundant in urinary 

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

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

 especially rich in phosphorus (wheat, bran, beans, peas, vetches, rape 

 cake, oil cake, cottonseed cake) ; and (&) when, through the morbid, 

 destructive changes in the living tissues, and especially of the bones, 

 a great quantity of phosphorus is given off as a waste product. 

 Under these conditions, however, the phosphates may contribute to 

 the formation of calculi, and this, above all, is liable if the urine 

 is retained in the bladder until it has undergone decomposition and 

 given off ammonia. The ammonia at once unites with the phos- 

 phate of magnesia 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 only in minute quantities. 



