In 1864 this slowly growing recognition of a specific cause received
further impetus from the statements of Megnier. This observer claimed to
have discovered in the cankerous secretions the existence of a vegetable
parasite (namely, a cryptogam, as in favus), which he termed the
keraphyton, or parasitic plant of the horn.
Modern research, though failing to substitute anything more definite, has
not confirmed this. The exact and exciting cause of canker is therefore
still an open question, and a matter for research. We may, however, sum the
matter up by briefly discussing the causes, so far as clinical observation
teaches us. This we shall do under two headings--namely, _Predisposing_ and
_Exciting_.
_Predisposing Causes_.--Starting with the assumption that the disease is
due to local infection, we may relate as predisposing causes anything
having a prejudicial effect upon the horn, disintegrating it, and so laying
the tissues beneath open to attack. The most prominent in this connection
is certainly a continued dampness of the material on which the animal
has to stand. Particularly is this the case when the material is also
excessively foul and dirty, contaminated with the animal discharges, and
presumably swarming with the lower forms of animal and plant life. We
shall therefore find bad cases of canker in stables where the "sets" are
irregular, or where no paving at all is attempted, where the drainage
is defective, and where darkness and want of proper ventilation favours
organismal growth.
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