DISEASES OF THE URINARY 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 isi 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 Weehler 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 (0) 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. 
