Skin Diseases. 279 



species — demodex — ^inhabits the sebaceous glands of the 

 skin in sheep and dog and causes much irritation with 

 cume-liJce eruption. Among acari occasionally parasitic 

 may be mentioned : the dermanyssus (misnamed hen louse), 

 the gamasus of musty hay, and the leptus (misnamed jigger 

 in the Western States), all excepting the last living on the 

 surface and easily discovered. Lastly a tyrocjlyph is acci- 

 dentally parasitic on all domestic animals. 



Of the sarcoptes there is one species lives on the horse, 

 which will temporarily inhabit the skin of man ; a second 

 is pecuhar to the goat ; a third is common to dogs and 

 swine, a fourth to cats and rabbits and a fifth to chickens 

 horses and foxes. 



One species of dermafophagics lives on the heels and legs 

 of horses, another on the tail, neck, etc., of cattle, and a 

 third on the pastern, Hmbs, and less frequently the trunk, 

 of sheep. 



Of dermatocoptes there is also a particular species for 

 each of these animals — horse, ox and sheep — though usu- 

 ally confounded with each other. These are the most 

 common causes of mange and from their non-bvuTowing 

 habits are most easily disposed of. 



Accessory causes. Though the reception of the acarus 

 is the one essential cause of mange, yet others conduce to 

 its speedy diffusion — as poor condition, filth and warm 

 seasons. Some acari, like the dermatopJiagi, may even 

 seem to suspend operations in winter and cause httle or 

 no trouble until the following spring. 



Symptoms. We must state these in general terms, 

 tlirowdng the whole class into one group. There is intense 

 uncontrollable itching, aggravated by hot weather or build- 

 ings, and by perspiration. If the affected part is scratched 

 the animal shows his gratification by moving his body as 

 if rubbing, and especially (in horses) by a nibbling move- 

 ment of the lips. In sheep the wool is torn off, and white 

 tufts hang on the dark surface of the fleece. The skin is 

 thickened and rendered rigid by exudation into its sub- 



