DISEASES OF THE SKIN. 477 



EPITHELIAL CANCER, OR EPITHELIOMA, 



This sometimes occurs on the lips at the angle of the mouth and 

 elsewhere in the horse. It begins as a small, wartlike tumor, which 

 grows slowly at first, but finally bursts open, ulcerates, and extends 

 laterally and deeply in the skin and other tissues, destroying them as 

 it advances (rodent ulcer). It is made up of a fibrous framework and 

 numerous round, ovoid, or cylindrical cavities, lined with masses of 

 epithelial cells, which may be squeezed out as a fetid, caseous mate- 

 rial. Early and thorough removal with the knife is the most suc- 

 cessful treatment. 



VEGETABLE PARASITES OF THE SKIN. 



(PI. XXXVIII, figs. 2, 3, 4.) 



Paeasite : Trichophyton tonswrans. Malady : Tinea tonsii/rans, or 

 oircinate ringworm. — ^This is especially common in young horses 

 coming into training and work, in low-conditioned colts in winter 

 and spring after confinement indoors, during molting, in lymphatic 

 rather than nervous subjects, and at the same time in several animals 

 that have herded together. The disease is common to man, and 

 among the domestic animals to horse, ox, goat, dog, cat, and in rare 

 instances to sheep and swine. Hence it is common to find animals of 

 different species and their attendants suffering at once, the diseases 

 having been propagated from one to the other. 



Sym/ptoms.—ri-n the horse the symptoms are the formation of a cir- 

 cular, scurfy patch where the fungus has established itself, the hairs 

 of the affected spot being erect, bristly, twisted, broken, or split up 

 and dropping off. Later the spot first affected has become entirely 

 bald, and a circular row of hairs around this are erect, bristly, broken, 

 and split. These in turn are shed and a new row outside passes 

 through the same process, so that the extension is made in more or 

 less circular outline. The central bald spot, covered with a grayish 

 scurf and surrounded by a circle of broken and split hairs, is char- 

 acteristic. If the scurf and diseased hairs are treated Math caustic- 

 potash solution and put under the microscope, the natural cells of the 

 cuticle and hair will be seen to have become transparent, while the 

 groups of spherical cells and branching filaments of the fungus stand 

 out prominently in the substance of both, dark and unchanged. The 

 eruption usually appears on the back, loins, croup, chest, and head. 

 It tends to spontaneous recovery in a month or two, leaving for a time 

 a dappled coat from the spots of short, light-colored hair of the new 

 growth. 



The most effective way of reaching the parasite in the hair follicles 

 is to extract the hairs individually, but in the horse the mere shaving 

 of the affected part is usually enough. It may then be painted with 



