exclusively made of silica.

(7) _Oxalate of lime calculi_ (_mulberry calculi_) (Pl. XI, fig. 2).--
These are characterized by their extremely rough, angular surface, formed
by the octahedral crystals of oxalate of lime. Their specific gravity may
be 3.441, and they contain oxalate of lime to the extent of 81 per cent,
together with carbonates of lime and magnesia and organic matter.

(8) _Gravel_ (_pultaceous deposits_).--Simple crystals may be met with at
any point from the kidneys to the external opening at the end of the
prepuce (sheath), and they may appear singly, as crystals, or they may
accumulate in masses of fine spherical crystals almost like dirty powdered
chalk suspended in water. In the ox this is especially common as a
collection in the sheath, distending that into a soft, doughy swelling.

FORMS OF CALCULI IN DIFFERENT SITUATIONS.

Apart from the rough crystalline surfaces of the calculi of oxalate of lime
and ammonio-magnesium phosphate, the general tendency is to a smooth, round
outline. At times, however, they show more or less flattening with rounded
angular edges, caused by the contact and mutual friction of two calculi.
Sometimes two or more stones lying together become united into one by a new
external deposit, and the resulting mass then shows rounded swellings on
opposite sides. The large calculi occupying the pelvis of the kidneys
usually show a central part having the outline of the main cavity of the
pelvis and two or more projections that have been molded into the
corresponding branches or channels which lead to corresponding lobes of the
kidney. In winter and spring small concretions in the form of plates are
often met with in the branches of the pelvis, having been formed and molded
in the confined space between the projecting papilla and the surrounding
cuplike branch of the pelvis. Finally, the pulplike deposits in the sheath
and elsewhere are made up of globular masses, individually so small as to
be often practically microscopic.

STONE IN THE KIDNEY (RENAL CALCULI).

[Pl. XI, fig. 1.]

In an animal leading the quiet, uneventful life of the ox, stones of
large size may be present in the kidney without producing any disorder
appreciable to the people about him. In cattle fattened on dry feed in
winter, on the magnesian limestone of New York, it is exceptional to find
the substance of the kidney free from calculi about the size of a grain of
wheat or less, and standing out as w