DISEASES OF THE FETLOCK, ANKLE, AND FOOT. 419 
a healthy horn by which the injury may be repaired. Heavy cart 
horses are more often affected than those of any other class. 
Causes.—The essential element in the production of canker is the 
parasite; consequently the disease may be called contagious. As in 
all other diseases due to specific causes, however, the seeds of the dis- 
order must find a suitable soil in which to grow before they are 
reproduced. It may be said, then, that the conditions which favor 
the preparation of the tissues for a reception of the seeds of this 
disease are simply predisposing causes. 
The condition most favorable to the development of canker is 
dampness—in fact, dampness seems indispensable to the existence 
and growth of the parasite; the disease is rarely, if ever, seen in 
high, dry districts, and is much more common in rainy than in dry 
seasons. Filthy stables and muddy roads have been classed among 
the causes of canker; but it is very doubtful whether these conditions 
can do more than favor a preparation of the foot for the reception 
of the disease germ. 
All injuries to the feet, by exposing the soft tissues, may render the 
animal susceptible to infection; but neither the injury nor the irrita- 
tion and inflammation of the tissues which follow are sufficient to 
induce the disease. 
For some unknown reason horses with lymphatic temperaments— 
thick skins, flat feet, fleshy frogs, heavy hair, and particularly with 
white feet and legs—are especially liable to canker. 
Symptoms.—Usually, canker is confined to one foot; but it may 
attack two, three, or all of the feet at once; or, as is more commonly 
seen, the disease attacks first one then another, until all may have 
been successively affected. When the disease follows an injury which 
has exposed the soft tissues of the foot, the wound shows no tendency 
to heal, but instead there is secreted from the inflamed parts a pro- 
fuse, thin, fetid, watery discharge, which gradually undermines and 
destroys the surrounding horn, until a large part of the sole and frog 
is diseased. The living tissues are swollen, dark colored, and covered 
at certain points with particles of new, soft, yellowish, thready horn, 
which are constantly undergoing maceration in the abundant liquid 
secretion by which they are immersed. As this secretion escapes to 
the surrounding parts, it dries and forms small, cheesy masses com- 
posed of partly dried horny matter, exceedingly offensive to the sense 
of smell. When the disease originates independently of an injury, 
the first evidences of the trouble are the offensive odor of the foot, 
the liquid secretion from the cleft and sides of the frog, and the 
rotting away of the horn of the frog and sole. 
In the earlier stages there is no interference with locomotion, but 
later the foot becomes sensitive, particularly if the animal is used on 
