DISEASES OF HORSES 309 



soldering bolt at a red heat, and any subsequent tendency to over- 

 growth kept down by bluestone. 



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 pealike masses, or as multiple tumors aggre- 

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

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

 exceptional 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 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 w r ith masses 

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

 rial. The most successful treatment is early and thorough removal 

 with the knife. 



VEGETABLE PARASITES OF THE SKIN. 



PARASITE: Trichophyton Tonsumns. MALADY: Tinea Tonsu- 

 rans, or Circinate Ringworm. 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 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. 



Symptoms. In the horse the symptoms are the formation of a 

 circular 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 en- 

 tirely 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 

 characteristic. If the scurf and diseased hairs are treated with caus- 

 tic 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 un- 

 changed. 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. 



