DISEASES OF THE SKIN. 337 



Cawea. It may arise spontaneously, or follow a scar after an injury. 



Symptoms. Kelis generally appears below the knee or hock. It may 

 occur singly or in numbers. There are no constitutional symptoms. 

 Its growth is very slow, and seldom causes any inconvenience. It 

 appears as a flattened, irregular or spreading growth within the sub- 

 stance of the skin, is hard to the touch, and is especially characterized 

 by divergent branches or roots ; hence the name is derived from its 

 resemblance to a crab. Occasionally some part of it may soften and 

 result in an abscess. It may grow several inches in length, and encircle 

 the whole limb. 



Treatment. So long as no inconvenience is manifested by the animal 

 it is best not to meddle with it; when it does, the animal ought to be 

 fattened for beef, the meat being perfectly harmless to the consumer. 



PARASITIC DISEASES OF THE SKIN. 

 SCABIES ACARIASIS MANGE ITCH. 



Mange is a disease of a local nature, due to a mite, which induces 

 irritation and incrustation on the surface of the body generally. It is 

 always contagious, requiring for its development the transplantation 

 of the parasites or their eggs from the diseased to the healthy animal. 

 This disease is not very common among cattle in this country, while in 

 some countries it prevails as an epizootic. Poor hygiene appears to 

 favor the extension of the disease, and it is claimed that weakened cat- 

 tle are more predisposed to harbor the parasite than strong, healthy 

 ones. It is also more prevalent in winter than in summer, and in the 

 latter season sometimes entirely disappears. 



Cattle are afflicted with two varieties of these parasites. They 

 belong to the class Arachnidw, genera, Fsoroptes (J)ermatodcctes) which 

 simply bite, and hold on to the skin; and Chorioptcn (nymbiotc.fi) living 

 together in large families, and not piercing further than the cuticle in 

 search of food. 



Psoroptcs commit nit var. 6ort* (Syn. Dermatodcctes communis, Der- 

 matocoptes coinmftnis). This is the most frequent one met in cattle. 

 It lives on the surface of the epidermis, and gives rise to much irrita- 

 tion by biting. It generally chooses the regions of the top of the shoul- 

 der and root of the tail for its habitation. From these localities it grad- 

 ually extends by increase in numbers, causing intense itching and 

 great digress in the affected animal. From the irritation of the skin 

 papular nodules appear, which develop into vesicles filled with fluid 

 and rupture. The drying of the exuding fluid forms crusts, and these 

 are liable to bo followed by ulccration. The hairs may project up 

 through the crust or fall out. In chronic cases the skin becomes thick- 

 ened and almost insensible, dry, and wrinkled. As it is easy to con- 

 found this disease with eczema, our sole dependence for a correct diag- 

 nosis rests upon the discovery of the parasite, or, at least, upon positive 



