o
impede the work of healing going on, and allows free movement of the foot
and pastern to take place. At the same time suffering and emaciation cease,
and the animal is rendered workable.[A]

[Footnote A: _Veterinary Record_, vol. ii., p. 371.]

C. CORONITIS (SIMPLE).

TREAD, OVERREACH, ETC.

1. _Acute_.

_Definition_.--Under the heading of simple coronitis in its acute form we
intend to describe those inflammatory conditions of the skin and underlying
structures of the coronet occurring without specific cause. Specific
coronitis will be found described in Chapter IX.

_Causes_.--This condition is almost invariably set up by an injury--either
a bruise or an actual wound--to the coronet. By far the most common among
such injuries are those inflicted by the animal himself by means of the
shoes.

That known as 'tread' is caused by the shoe on the opposite foot, and may
happen in a variety of ways. More often than not it is met with in the feet
of heavy draught animals, and is there caused by the calkin, either when
being violently backed or suddenly turned round. It may also occur in
horses with itchy legs, as a result of the animal rubbing the leg with the
shoe of the opposite limb. The irritation in this case is nearly always
due to parasitic infection (_Symbiotes equi_), and becomes sometimes so
unbearable as to render the animal unmindful of the injury he may be
inflicting so long as he experiences the relief obtained by the rubbing.

Self-inflicted tread is also sometimes met with when horses are worked
abreast at plough. The animal in the furrow, with one foot sometimes in and
sometimes out of the hollow, is caused to make a false step, and so brings
the injury about.

Animals worked in pairs are further liable to receive a tread from the foot
of their companion. This is commonly seen in heavy animals at agricultural
labour in fields, where the walking is uneven, and abrupt turning constant.
It is not uncommon either in animals at work in vans in town, and is
occasionally met with in the feet of carriage-horses.

'Overreach' is the term used to indicate the injury inflicted on the
coronary portion of the heel of the fore-foot by the shoe of the hind.
Ordinarily, overreach occurs when the animal is at a gallop, and is thus
met with in its severest form in hunters and steeplechasers. It can only
occur when the fore-foot is raised from the ground and the hind-foot of the
same side reached right forward. W