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. 
(Pl. XXXVIII, figs. 2, 3, 4.) 
Parasite: Trichophyton tonsurans. Mauapy: Tinea tonsurans, or 
circinate ringworm.—tThis 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. 2 
Symptoms.—tin 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 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 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 
