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 all, but a delicate structure. When attacked by the application of too potent a drug its horn-secreting layer is easily destroyed, and thus, although we may succeed in establishing asepsis, we cannot expect at the point of injury a growth of horn. In its place we are confronted with large outgrowths of inflammatory fibrous tissue. (3) Shedding of the diseased horn and removal of the pressure exerted by the hoof faces us with hypertrophy of the exposed villi. The difficulty of meeting this with an adequate and evenly-distributed pressure is well enough known, and we find in that a further reason that the treatment of canker is superlatively difficult. (4) The material on which the animal has to stand is a distinct bar to the maintaining of a strict asepsis.

When we have said this, it is easy to understand that canker is not to be successfully met with any so-called specific - that it makes but little difference what the application may be so long as it is antiseptic, and is used by a man thoroughly conversant with the difficulties he has to contend with, and with his mind firmly set upon surmounting them.

With this point established, we will not devote more of our space to a consideration of the various dressings that have at different times been highly advocated in the treatment of the disease. It is interesting, however, to note that intensely irritating and caustic applications have been greatly in favour. Nitric acid, sulphuric acid (either alone or its action reduced by the addition of alcohol, oil, or turpentine), arsenic, butter of antimony, creasote, chromic acid, carbolic acid, arsenite of soda, and the actual cautery, have all been used.

Without dwelling further on that, we may say at once that a correct treatment consists in (1) the removal of all horn overlying infected portions of the keratogenous membrane, (2) the application of an antiseptic not too powerfully caustic in its action, (3) frequent changes of the dressings in order to insure a maintenance of antisepsis, and (4) the application of an adequate pressure to the exposed soft structures. Thus combated, canker is curable.

The man who, at the expense of much time and trouble, has demonstrated the truth of these axioms is Mr. Malcolm, of Birmingham. The determination with which he clung to his point that canker was, with correct treatment, in every case curable, was some years ago provocative of much discussion in veterinary circles. That he was successful in proving his contention is more to our point here. It is his method of treatment, therefore, that we shall give, and this we shall do by liberal extracts from Mr. Malcolm's own writings.

'On the first occasion of operating upon and dressing the cankered foot, it is usually necessary to cast the horse, and this may have to be done at intervals for a second or even third time; but in most cases once is sufficient, subsequent dressing being usually accomplished without much difficulty, frequently even without the aid of a twitch. After the horse has been secured, the drawing-knife is first employed; and if the frog alone is affected, it is unnecessary even to pare the sole, the removal of all frog horn not intimately adherent to its secreting surface being all that is required. But if both sole and frog be involved, the whole of the sound horn should be first thinned until it springs under the thumb, and then, using a sharp knife, every particle of diseased horn must be carefully removed from both sole and frog, a process much more easily, and with far greater certainty, secured by the previous thinning of the horn.

'The removal of diseased horn should always commence at the most dependent part of the foot, so that any haemorrhage produced may be below the parts still to be operated on, a matter of considerable moment for effective treatment. But with due care there will be little haemorrhage, as, except in the initial stage, there is no real union between the diseased horn and the diseased vascular secreting surface.

'After all apparently diseased horn has been removed by the knife, any still remaining should be at once destroyed by the actual cautery, by which it can be identified. All the diseased secreting surface should be carefully scraped with a thin hot iron,[A] fungoid growths excised and cauterized, and, indeed, every particle of cankered tissue should, if possible, be eradicated. In securing this more reliance can be placed on the actual cautery than on any other, whether liquid or solid: it is more under control in application, more decisive in effect, and its results can be anticipated with a far greater certainty. Moreover, its aid in diagnosis is of immense value; applied to the thinned horn or secreting surface it unmistakably demonstrates the presence or absence of canker. Healthy tissue chars black; cankered tissue, on the contrary, bubbles up white under the hot iron, and presents an appearance not unlike roasted cheese.

[Footnote A: The words in italics are alterations in the original article made by Mr. Malcolm in a private letter to the author (H.C.R.).]

'Although this test is certain for horn thinned to the quick, it is not to be relied upon with thick horn, the outside of which may be practically healthy and char black, while its underlying surface may be cankered. With this exception the test is an infallible one, as by it the demarcation between cankered and healthy tissue can be clearly traced, and as a result we can with equal confidence radically remove[A] all cankered tissue, and conserve all healthy. As the object of that abominably cruel and barbarous operation of stripping the sole is the exposure of all canker, and as this can be done with equal certainty with the aid of the hot iron, there can be no necessity for performing it. The pain of cauterizing cankered tissue, which is a necessary operation, is infinitesimal (canker largely destroying sensation), compared with the pain produced in the totally unnecessary process of tearing healthy horn from a highly sensitive tissue.

[Footnote A: The words in italics are alterations in the original article made by Mr. Malcolm in a private letter to the author (H.C.R.).]

'Having by means of the knife and cautery removed every known particle of disease, the next procedure is to pack the surface of the sole and frog thus exposed with a mild dressing, such as vaseline; but if the cankered surface has not been efficiently, scraped, than there is required a more [A] powerful astringent or caustic dressing, which may vary considerably according to the individual fancy. A great favourite of mine consists of equal parts of sulphates of copper, iron, and zinc, mixed with strong carbolic acid, a very little vaseline being added to give the mass cohesion. The dressing, covered by a pledget of tow, is held in position by a shoe with an iron or leather sole, and the dressing and tow together should be of sufficient bulk to produce slight pressure on the sole when the nails of the shoe are drawn up. This insures contact between the dressing and the exposed surface, as well as any benefit derivable from pressure.

[Footnote A: The words in italics are alterations in the original article made by Mr. Malcolm in a private letter to the author (H.C.R.).]

'The dressing of the foot and nailing of the shoe can usually be more expeditiously performed when the horse is on his feet than when prone. If only the frog, or the frog and a small part of the sole, be involved, the horse should be kept at work, but if a large part or the whole of the sole a few days' rest may be necessary; but as soon as the condition of the foot will allow, work should be resumed, and it is simply marvellous how sound a horse will walk while minus the greater part of his sole from canker.