DISEASES OF THE HORSE. 449 



BLACK PIGMENT TUMORS, OR MELANOSIS. 



These are common in gray and in white horses on the naturally black 

 parts of the skin at the root of the tail, around the anus, vulva, udder,, 

 sheath, eyelids, and lips. They are readily recognized by their inky- 

 black color, which extends throughout the whole mass. They may 

 appear as simple pea-like masses, or as multiple tumors aggregating 

 many pounds, especially around the tail. In the horse these ara 

 usually simple tumors, and may be removed with the knife. In excep- 

 tional cases they prove cancerous, as they usually are in man. 



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 wart-like 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 material. 

 The most successful treatment is earl}^ and thorough removal with the-, 

 knife. 



VEGETABLE PARASITES OF THE SKIN. 



Parasite: Trichophyton tonsxirans. Malady: Tinea tonsurans, or 

 Circinate ringtoorni. — This is especially common in young horses^ 

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

 spring after confinement indoors and during moulting, in Ij^mphatic 

 rather than nervous subjects, and at the same time in se^^eral 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. 



Symjyto^ns. — In the horse the symptoms are the formation of a circu- 

 lar scurfy patch where the fungus has established itself, the hairs of 

 the affected spot being erect, bristly, twisted, I)roken, 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 sur- 

 rounded by a circle of broken and split hairs, is characteristic. If th& 

 scurf and diseased hairs are treated with 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 prominentlj^ in the 

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