DISEASES OF THE HORSE. 477 



incision and thoroug-hly sear all parts of the walls of the abscess. 

 This is to be repeated after the first slough has taken place, if the 

 walls remain thickened and indurated. 



It is useless to waste time with fomentations, poultices, or blisters 

 in the treatment of cold abscesses, since, though apparently removed 

 by such methods, they almost invariably return when the horse is put 

 to work. Extirpation by the knife is not practicable, as the walls of 

 the tumor are not sufficiently defined. If treated as above directed, 

 and properl}^ fitted with a good collar after healing, there will not 

 remain any track or trace of the large, unsightly mass. 



FISTULAS. 



Definition. — The word fistula is applied to any ulcerous lesion upon 

 the external surface of the body which is connected b}^ ducts, or pas- 

 sages, with some internal cavity. Because of this particular formation 

 the term fistulous tract is often used synonymousl}^ with the word fis- 

 tula. Fistulas may exist in any part of the body, but the name has 

 come to be commonly accepted as applicable only to such lesions when 

 found upon the withers. Poll evil is a fistula upon the poll, and in no 

 sense differs from fistulous withers except in location. The descrip- 

 tion of fistula will apply, then, in the main, to poll evil equalh^ well. 

 Quittor presents the characteristic tubular passages of a fistula and 

 may therefore be considered and treated as fistula of the foot. Fistu- 

 lous passages may also be developed upon the sides of the face, through 

 which saliva is discharged instead of flowing into the mouth, and are 

 called salivary fistulne. A dental fistula may arise from the necrosis 

 of the root of a tooth. Again, a fistula is sometimes noted at the 

 umbilicus associated with hernia, and recto-vaginal fistulas have been 

 developed in mares, following difficult parturition. Fistulas m&j arise 

 from wounds of glandular organs or their ducts, and thus we have the 

 so-called mammary, or lachrymal, fistulas. 



Fistulous tracts are lined with a false, or adventitious, membrane 

 and show no disposition to heal. The}^ constantly afford means of exit 

 to the pus or ichorous material discharged by the unhealthy parts 

 below. They are particularly liable to develop at the withers or poll 

 because of the exposed positions which these parts occup}^ and, having 

 once become located there, they usually assert a tendenc}'^ to farther 

 extension, because the vertical and laminated formation of the muscles 

 and tendons of these parts allows the forces of gravitation to assist the 

 pus in gaining the deeper-lying structures and also favors its retention 

 among them. 



Causes. — Fistulas follow as a result of abscesses, bruises, wounds, or 

 long-continued irritation by the harness. Among the more common 

 causes of fistula of the poll (poll evil) are chafing by the halter or heavy 

 bridle; blows from the butt end of the whip; the horse striking his head 



