650 
CRACKED-HEELS—GANGRENOUS DERMATITIS—GREASE. 
factois, partly of an infectious, partly of a chemical character, are also at 
woih. Slight injuries to the lower portions of the limb lead to septic 
infection, which may result in inflammation, and when assisted by 
cold, in gangrene. Low temperatures depress the vitality of existing 
wound sin faces and thus favour septic bacilli in obtaining a lodgment. 
Y\ hatevei view may finally prove correct, thus much is certain, that as a 
lule infection acts along with cold in giving the first impulse to the pro¬ 
duction of gangrenous dermatitis. The cases seen about the coronet and 
fiont of the pastern are often initiated by “ treads ” ; the horse injuring 
the skin with the calkin of the opposite shoe, and the wound becoming 
infected. That this form of dermatitis does occur, in exceptional 
instances, even in the warm season, only shows that gangrene of the 
skin may be produced independently of cold. 
Symptoms and course. The disease appears suddenly, generally over¬ 
night. Theie is severe lameness in one or other limb, with inflammatory 
swelling of its lower portions, sometimes also of the upper parts. Fever 
is also common. Closer examination detects at a given spot a portion of 
skin, fiom 1 to 2 inches in diameter, which is soft, yielding, and swollen : 
piessuie over this spot causes severe pain, and produces discharge of a 
reddish turbid fluid. The pastern is the most common seat of disease, at 
a point just over the bulb of the heel, or on the anterior surface near the 
coronet. The pain continues, the limb increases in size, and in two to 
three days the gangrenous portion of the skin is cast off as a soft, grey, 
slimy mass: the resulting wound then becomes covered with granulations, 
which giadually fill up the cavity. In favourable cases a cicatrix forms, 
and recovery is complete in one to two weeks. 
Lut the disease does not always take so favourable a course ; sometimes 
the gangrenous inflammation extends downwards to the lateral cartilage, 
or the coronet bone, or penetrates to the sheath of the flexor tendon. In 
the first case a quittor forms, in the second an exostosis, wTiich later 
becomes a ring-bone. And if in such cases suitable treatment often 
leads to recovery, i.e., to removal of lameness, yet when the sheaths 
of the tendons are also attacked, death usually occurs in a short time 
from septicaemia or pyaemia. If the necrotic process extends to the 
coionaiy vessels, pyaemia is apt to result. In the neighbourhood of 
the coronet, gangrene may extend to the coronary band, and produce 
severe inflammation, followed by loss of the hoof. 
Prognosis depends on the extent, position, and character of the disease. 
The larger the gangrenous piece of skin, the greater the difficulty of 
tieatment, and the danger to deeper-lying structures. Gangrene near 
the coronet threatens the pedal-joint, in the pastern the sheaths of the 
flexoi tendons. Implication of tendon sheaths at once renders prognosis 
unfavourable. The same is true of complications like septicaemia and 
