Differential Diagnosis and Prognosis.—­Perhaps the only disease with which canker may be confounded is thrush.  They should, however, be easily distinguishable.  The discharge from thrush is not so profuse, and is thicker and darker in colour, while the loosening of the horn is almost entirely absent.  Furthermore, thrush shows no tendency to spread, and, even when left untreated, may remain confined to the frog for months, and even years.  Canker, on the other hand, is slowly progressive, and soon shows the characteristic fungoid excresences, which growths are in thrush never seen.  A further point of difference is discovered when treatment is commenced.  Canker is found to be refractory to a point that is absolutely disheartening, while thrush, with careful attention, is soon got under hand, and a permanent cure effected.

The prognosis must be guarded.  By many canker has been said to be incurable.  This, however, has been clearly shown to be wrong.  When the animal is young, and treatment may reasonably be judged to be economical, then a favourable prognosis may be indulged in, provided the veterinary surgeon intends to put into that treatment a more than ordinary amount of individual care and attendance.  Even then, however, he will have to be very largely guided by the condition of his case.  He should see that it is not too far advanced, and that a great deformity of the hoof, or actual exploration, does not indicate disease of the greater part of the wall.

Treatment.—­From what has gone before, it will be seen that the eradication of canker is no easy task, that it is, in fact, a most difficult matter, and one not to be lightly undertaken.  At the risk of recapitulating what we have said before, we may mention here the two points which the veterinarian must bear in mind. (1) That there is no actual disease or alteration in structure of the deep layers of the keratogenous apparatus.  It is only the superficial, or horn-secreting, layer that concerns us. (2) That the disease of this superficial layer is infection with a material that may reasonably be presumed to be infective.

Put thus, treatment of canker would at first sight appear to be easy.  One would imagine that a simple and long-continued soaking of the entire foot in a strong enough antiseptic would be all that was needed.  Clinical observation, however, shows that this is not so, and for this there must be reasons.

The reasons are these:  (1) Between us and the diseased layer upon which our attention must be directed is often a layer of normal horn, effectually protecting the tissues beneath from any dressing which we might consider beneficial. (2) Anything applied with the object of destroying septic material, but strong enough, or caustic enough, to injure the membrane upon which we are working, only makes the case worse.  The superficial layer of the keratogenous membrane in which we have judged the disease to exist is, after