sulting in
hematuria or hemoglobinuria; sprains or other injuries to the back, or
disease of the spinal marrow, which cause the escape of blood with the
urine; the presence in the bladder of a bacterial ferment, which determines
the decomposition of the mucus and urea, the evolution of ammonia and the
consequent destruction of the protecting cellular (epithelia) lining of the
bladder, or the irritation caused by the presence of an already formed
calculus, may produce the colloid or uncrystallizable body that proves so
effective in the precipitation of stone or gravel. It has long been known
that calculi almost invariably form around any foreign body introduced into
the kidney or bladder, and I have seen a large, calculous mass surrounding
a splinter of an arrow that had penetrated and broken off in the body of a
deer. The explanation is now satisfactory--the foreign body carries in with
it bacteria, which act as ferments upon the urine and mucus in addition to
the mechanical injury caused by its presence. If such a body has been
introduced through the solid tissues, there is, in addition, the presence
of the blood and lymph derived from the wounded structures.

CLASSIFICATION OF URINARY CALCULI.

Urinary calculi are most conveniently divided according to the locality in
which they are found. Thus we find first renal calculi, formed in the
kidney (Pl. XI, fig. 1), and which for cattle must be again divided into
calculi of the uriniferous tubes and calculi of the pelvis. The second
class are named ureteral calculi because they are found in the duct leading
from the kidney to the bladder (ureter). The third class are the vesical
calculi, from the bladder or vesicle in which they are found. The fourth
class are the urethral calculi, and are found in the duct leading outward
from the bladder through the penis (urethra). The fifth and last class are
the preputial calculi, since they are found within the sheath of the penis
(prepuce).

Calculi may also be classed according to their chemical composition and
this has the advantage of suggesting the special cause of each as found in
the feed, water, soil, or general conditions of health. This classification
affords no guide to their location or symptoms, as calculi of the same
chemical composition may be formed at any part of the urinary passages, as
those formed in the kidney may pass on through all the various passages
outward, unless it is found at any point of their progre