In a nag-horse with thrush of both fore-feet lameness becomes sometimes very great.  The gait when first moved out from the stable is feeling and suggestive of corns, while progress on a road with loose stones is sometimes positively dangerous to the driver.

Treatment.—­When this condition has arisen, as it often does, from want of counter-pressure of the frog with the ground, this pressure must be restored after the manner described when dealing with the treatment of contracted foot (see p. 125) either by the use of tip or bar shoes, or by suitable pads and stopping.

So far as direct treatment of the lesion itself is concerned, the first step is to carefully trim away all diseased horn and freely open up the lacunae in which the discharge has accumulated.  Good results are then often arrived at by poulticing, afterwards followed up by suitable antiseptic dressings.  With us a favourite one is the Sol.  Hydrarg.  Perchlor. of Tuson, used without dilution.  Others use a dry dressing, and dust with Calomel, with a mixture of Sulphate of Copper, Sulphate of Zinc and Alum, or with Subacetate of Copper and Tannin.

With restoration, so far as is possible, of the frog functions, and with careful dressing, a cure is nearly always obtained.

6.  CANKER.

Definition.—­Under this unscientific, yet expressive term, is indicated a chronic diseased condition of the keratogenous membrane, commencing always at the frog, and slowly extending to the sole and wall, characterized by a loss of normal function of the horn secreting cells, and the discharge of a serous exudate in the place of normal horn.

Causes.—­The exact cause of canker has still to be discovered.  Therefore, before expressing an opinion as to what the probable cause may be, we may state here that such opinion can only be based upon clinical observation.  Such being the case, we are almost duty bound to give the views of older authors before those of more modern writers.

From the mass of material ready to hand we may select the following as serving our purpose.

The earliest opinion appears to have been that canker, as the name indicates, was of a cancerous or cancroid nature.  This was also believed by Hurtrel D’Arboval, who looked upon canker as carcinoma of the recticular structure of the foot.  The same theory we find enunciated in the Veterinary Journal so late as 1890.  Although the word ‘cancer’ or ‘carcinoma’ is not there used, the author employs the terms ‘Papilloma’ and ‘Epithelioma’ with the evident intention of expressing his belief in the malignant nature of the disease.

Another early opinion was that the disease was a spreading ulcer, gradually extending and changing the tissues which it invaded.