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 buists open, ulcerates, and extends 

 laterally and deeply in the skin and other tissues, de;^troying tiieni 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 remo\al with the knife is the most suc- 

 cessful treatment. 



VEGETABLE PARASITES OF THE SKIN. 



(I'l. XXXVIII, (It's. -J, ::, 4.1 



Parasite: Trlehophytun tonsurans. jNIaladt: Tinea tonswvaiui^ or 

 c-trc'inate rmgicorm. — This is especially conunon in young horses 

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

 and spring after confinement indoors, during molting, in lympiiatic 

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

 tliat have herded together. The disease is conunon 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, tlie diseases 

 having been propagated from one to the other. 



Symptoirm. — In the hoi*se the sym})toms are the fcuination of a cir- 

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

 of the affected spot being erect, bristly, twi.sted, 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 surroimded by a circle of broken and split hairs, is char- 

 acteristic. If the scurf and diseased liairs are treated with cau.stic- 

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

 cuticle and hair will be seen to have beeome transjiarent, while the 

 groups of spheiical cells and branching filaments of the fungus stand 

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

 eruption usually appeal's on the back, loins, croiij), chest, and head. 

 It tends to si)ontaneous recovery in a month or two, leaving for a time 

 a <lapple<.l 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 hoi-se the mere shaving 

 of the affected part is usually enough. It may then Ik- ]iaint^d with 



