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.