PARASITES OF THE SKIN. 449 



mostly seen in young horses, about the lips, eyelids, cheeks, ears, 

 beneath the belly, and on the sheath, but may develop anywhere. 

 The smaller ones may be clipped off with scissors and the raw surface 

 cauterized with bluestone. The larger may be sliced off with a sharp 

 knife, or if with a narrow neck they may be twisted off and then cau- 

 terized. If very vascular they may be strangled by a wax thread or 

 cord tied around their necks, at least three turns being made round 

 and the ends being fixed by passing them beneath the last preceding 

 turn of the cord, so that they can be tightened day by day as they 

 slacken by shrinkage of the tissues. If the neck is too broad it may be 

 transfixed several times with a double-threaded needle and then be 

 tied in sections. Very broad warts that can not be treated in this way 

 may be burned down to beneath the surface of the skin with a solder- 

 ing bolt at a red heat, and any subsequent tendency to overgrowth 

 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 with masses of 

 epithelial cells, which may be squeezed out as a fetid caseous material. 

 The most successful treatment is early and thorough removal with the 

 knife. 



VEGETABLE PARASITES OF THE SKIN. 



PARASITE : Trichophyton tonsurans. MALADY : Tinea tonsurans, 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 

 H. Doc. 795, 59-2 29 



