The Potential Cautery. - This is employed in the treatment of sub-horny quittor, either in the solid form (in sticks, in lumps, or in the powder), or in the liquid form, when it is injected with a quittor syringe.

In the former method such drugs as perchloride of mercury in the lump, or nitrate of silver, chloride of zinc, and caustic potash or soda in the stick, are introduced into each of the sinuses present. This is done by means of a director or a probe.

A better method, however, when the dressing lends itself to the purpose, is to use it in the form of a powder, wrapped in the form of small cubes in extremely thin paper, such, for instance, as is used for rolling cigarettes. It is then conveniently inserted into each fistula. Introduced in this more finely divided form the drug is, perhaps, a little more active in bringing about the desired result.

This method of 'plugging,' although practised by many, we cannot recommend in preference to the use of the hot iron or of liquid injections. Our reasons are these: the action of the drug is a protracted one. Almost immediately after its introduction into the fistula there is formed about it an almost impermeable layer of a metallic albuminate, which effectively prevents further rapid action of the caustic. In addition to thus preventing further action of the dressing, this combination of the tissue albumin with the metal of the salt, together with much necrotic tissue that it has caused, is extremely hard to remove from the healthy tissues. This we explain by pointing out that the action of the caustic, prolonged as it is, sets up a tissue reaction which partakes largely of the type of a chronic rather than an acute inflammation. With a chronic inflammation there is sooner a tendency to the production of fibrous tissue (and thus the firmer attachment of the necrosed portions) rather than an active phagocytosis and the casting-off of a slough. Again, careful though we may be with the probe, it is extremely difficult to be certain that we have discovered the whole extent of any fistula. An equal difficulty, therefore, exists in being certain that we have placed the caustic in the position in which it is most wanted - namely, at the furthermost end of the fistula where the necrotic tissue is to be found.

When a caustic is used at all, it is far better to employ it in the liquid form, when either of the drugs we have just mentioned may again be used. In the first place, the liquid is far more likely to be brought into contact with the diseased structures than is the solid salt. Also, its action may be regulated by altering the strength of the solution, and the liability to form impermeable albuminates thus diminished.

Probably the best solution for use in this way is the old-fashioned Villate's solution (see p. 199).

This liquid should be injected at least every day, and, in a bad case, even two or three times daily. Practical hints to be borne in mind when attempting to cure quittor by means of injections are these:

If the fistulas are numerous, the fluid should be injected into their various orifices.

In order to force the fluid to the bottom of each diseased track, it is necessary, when injecting one opening, to firmly close all others.

Several injections should be made at each time of injection. In other words, we must not be content with just forcing fluid in. It must be forced in, and again forced out by a further syringeful. The fistulous tracks must, in fact, be washed in the liquid.

The effect of the injection during the first eight or ten days is to render suppuration more abundant and whiter. After two weeks of the treatment sloughing of the inside of the sinuses occurs, and healing of the wound commences. Signs that this is occurring are - slight haemorrhage at the end of each injection, and a gradually increasing difficulty in forcing in the fluid.

The Making of Counter-openings to the Fistulas. - Although Villate's solution or any other caustic used in the manner we have described often effects a cure, many practitioners insist on the fact that a counter-opening to the fistula must also be made.

The probe is used and the direction and depth of the fistula ascertained. Through the wall is then made an opening at exactly opposite the lowest point found by the probe, or through the sole if the probe should there lead us. This opening is best made with a sharp-pointed iron, and may afterwards be kept large enough by an occasional trimming with the knife. Many of the older authors, and with them writers of the present day, declare that unless this is done the ordinary injection is likely to fail in a great many instances where it would otherwise have been successful.

Where a counter-opening is thus made it is found that it very readily closes with granulation tissue, and the purpose for which it was made defeated. This may be avoided by the use of a seton. In preference to the seton, however, we ourselves would advise that the opening be kept free by the occasional use of a sharp-edged director or a fine scalpel.

An interesting modification of the practice of making a counter-opening is that related by Veterinary-Captain S.M. Smith.[A] In point of severity it runs a middle course between the making of a simple counter-opening and the removal of a wedge-shaped portion of the coronary band and the wall, a method which we shall later describe.

[Footnote A: Veterinary Record, vol ii., p. 157.]

To perform this operation, the animal is cast and chloroformed. The foot is fixed and the parts thoroughly cleansed. The horn of the wall is then sawed through in a direct line from the coronary margin to the solar edge, the saw-line running exactly over the seat of the sinus.

A strong scalpel is now introduced at the coronary opening, with its cutting-edge outwards, and is gradually passed down the opening made by the saw. In this way the sinus is completely destroyed, and from end to end converted into an open wound. The parts are then washed in a perchloride of mercury solution, covered with a mixture of powdered iodoform and boracic acid, over which a pledget of carbolized tow is placed, and then a bandage over the whole. This dressing should be left on three or four days, after which the injury should be treated as an ordinary wound. In conclusion, the author says: 'I can safely recommend this line of treatment to any practitioner having an obstinate case under treatment.'

Removal of the Wall and Excision of the Necrotic Tissue. - This we may term the radical operation for sub-horny quittor, for it is often productive of a successful issue when all other means have failed. No matter in what position the sinus is, whether at the extreme anterior portion of the coronet, or whether in the region of the heels, it is to be thoroughly opened up. To do this, the fistula is carefully explored with the probe and a knowledge of its exact dimensions arrived at. This is carefully noted, and the horn of the wall for some little distance around it then rasped down quite thin. Immediately over the sinus, and for a short distance on either side of it, the horn is stripped away to the sensitive structures. The cavity of the fistula is then opened up with a scalpel, and every particle of diseased tissue removed with this instrument and a pair of forceps. After-dressing consists simply in the application of suitable antiseptics.