inciples, and therefore those that are the most easily and
speedily converted into urea, are present only to the amount of two-thirds
of that which exists in the wheat bran. With such an excess of ash, of
phosphates, and of nitrogenous (urea-forming) constituents in wheat bran,
its tendency to favor the formation of calculi is fully explained. It must
not, however, be inferred that wheat bran is not a valuable feedstuff. The
inference is only that it should be fed with an abundance of water, as a
sloppy mash, or in combination with an abundance of roots, potatoes,
pumpkins, or other succulent aliment.

In this connection the presence of magnesia in the feed or water must be
named as favoring calculous formations in the urinary passages. The
explanation is that while the phosphate of magnesia thrown out in the urine
is soluble in water, the compound phosphate of ammonia and magnesia is
insoluble, and, accordingly, if at any time ammonia is introduced into
urine containing the phosphate of magnesia there is instantly formed the
ammonio-magnesium phosphate, which is as promptly deposited in the solid
form. The common source of ammonia in such cases is from decomposition of
the urea in fermenting urine. In order to produce this a ferment is
necessary, however, and therefore, as an additional prerequisite, the
presence of bacteria, or fungi, in the urine is essential. These ferments
may make their way from without along the urinary passage (urethra), and
their propagation in the bladder is greatly favored by the prolonged
retention of urine, as in case of spasm of the neck of the bladder or
obstruction by an already existing stone. Another mode of entrance of the
ferment is an unclean catheter used to draw the urine. Still another is the
elimination through the kidneys of the bacteria of infectious diseases, or
of such as, without producing a general infection, yet determine
fermentation in the urine. The precipitation is favored not only by the
production of ammonia, but also by the formation of viscid (colloid)
products of fermentation. In this sense bacteria are most important factors
in causing gritty deposits in the urine.

Another insoluble salt which enters largely into the composition of many
urinary calculi of the ox is carbonate of lime. This is derived mainly from
the lime in the feed and water and from the carbon dioxid formed by the
oxidation of the organic acids in the fodder. These organic acids, being
compose