he absence of the fetid, greasy discharge, and finally a
tendency to form pus loosely in the tissues without any limiting
membrane, as in abscess. Another distinctive feature of grease is its
tendency to implicate the skin which secretes the bulbs or heels of the
horny frog and in the cleft of the frog, constituting the disease known
as canker.

_Causes._--The predisposing causes of grease are essentially the same as
those of simple inflammation of the heel, so that the reader may consult
the preceding section. Though a specific fungus and bacteria of
different kinds are present, they tend mainly to aggravation of the
disease, and are not proved to be essential factors in causation.

_Symptoms._--The symptoms vary according to whether the disease comes on
suddenly or more tardily. In the first case there is a sudden swelling
of the skin in the heel, with heat, tenderness, itching, and stiffness,
which is lessened during exercise. In the slower forms there is seen
only a slight swelling after rest, and with little heat or inflammation
for a week or more. Even at this early stage, a slight, serous oozing
may be detected. As the swelling increases, extending up toward the hock
or knees, the hairs stand erect, and are bedewed by moisture no longer
clear and odorless, but grayish, milky, and fetid. The fetor of the
discharge draws attention to the part whenever one enters the stable,
and the swollen pastern and wet, matted hairs on the heel draw attention
to the seat of the malady. If actively treated, the disease may not
advance further, but if neglected the tense, tender skin cracks open,
leaving open sores from which vascular bleeding growths grow up,
constituting the "grapes." The hair is shed, and the heel may appear
but as one mass of rounded, red, angry excrescences which bleed on
handling and are covered with the now repulsively fetid, decomposing
discharge. During this time there is little or no fever, the animal
feeds well, and but for its local trouble it might continue at work.
When the malady extends to the frog, there is a fetid discharge from its
cleft or from the depressions at its sides, and this gradually extends
to its whole surface and upon the adjacent parts of the sole. The horn
meanwhile becomes soft, whitish, and fleshy in aspect, its constituent
tubes being greatly enlarged and losing their natural cohesion; it grows
rapidly above the level of the surrounding horn, and when pared is found
to be pene