Apart from severe injury, a particularly troublesome form of coronitis may arise from the condition of the roads.  We refer to the conditions attendant on a thaw after snow.  The animal is called upon to labour in, or perhaps stand for long periods in, a mixture of snow and water, or snow and mud.  That this must have a prejudicial effect upon the structure of the coronet is plain.  The circulation of the part, already predisposed to sluggishness by reason of its distance from the heart, is farther impeded by the action of the cold.  Small abrasions of the skin, so small as to scarce be noticeable, are in this case freely open to infection with the septic matter the mud contains.  Necrosis and consequent sloughing of the skin is bound to follow, and an extensive ulcerous wound, or a spreading suppuration of the coronary cushion is the result.

Symptoms.—­We will take first the case in which no actual wound is observable.  Here the first indication of the trouble is the appearance of an inflammatory swelling, confined usually to one side, but extending sometimes to the whole of the coronet.  Always the part is hot and tender, and with it the patient is lame—­so much so, in many cases, as to be unable to put the foot to the ground, the toe alone being used.

In a mild case, uncomplicated by septic infection, these symptoms rapidly subside, and resolution occurs.

Always, however, the presence of septic infection must be suspected and looked for.  When this has occurred, the inflammatory swelling becomes larger and more diffuse, and the animal fevered.  This is then followed by a slough of the injured part.  A portion of the skin first becomes gray, or even black, in appearance, and around it oozes an inflammatory exudate, or even pus.  The skin immediately adjoining the spot of necrosis is swollen and hyperaaemic, and extremely painful and sensitive.  Later, the necrosed portion becomes cast off, and an open wound remains.  This as a rule marks the turning-point in the case.  The pain and other symptoms rapidly abate, and the wound, with proper attention, is not more than ordinarily difficult to treat.

In the case of an actual wound the symptoms are probably less severe.  The injury is, in this instance, the sooner detected, and remedial measures put into operation.  In this manner the formation of septic material is often checked, and nothing but the treatment of a simple wound demands attention.

There are, however, complications.

Complications—­(a) Diffuse Purulent Inflammation of the Sub-coronary Tissue.—­This condition is brought about by the spread into the loose tissue of the coronary cushion of the septic material introduced by the tread.  The whole coronet in this instance becomes excessively swollen, hot, and painful, and the dangerous nature of the complication is evident enough when the structure and situation of the parts involved is considered.  The amount of tendinous and ligamentous material in the neighbourhood offers a strong predisposition to necrosis, and the necrosis, with its attendant formation of pus, offers a further danger when the close proximity of the pedal articulation and the unyielding character of the horny box is considered with it.