MANGE. 135 



term, however, being a convenient one, is often indiscriminately 

 and incorrectly applied to any skin eruption which, like true (that 

 is, parasitic) mange, is accompanied by itching and the formation 

 of scabs. 



VARIETIES. — The following are the three species of these 

 insects : — 



1. The most common form of mange insect is psoroptes, which 

 chiefly invades those parts covered with " horse-hairs." They 

 infest the mane and tail, and may spread to the space between 

 the branches of the lower jaw, the breast, and thighs. As they 

 live in colonies, their seat of attack may at first be within narrow 

 limits, which gradually extend outwards. In this way, the 

 invaded portions of skin become united, until a considerable 

 surface is implicated. Owing to the more settled habits of these 

 parasites, this kind of mange is not so contagious as the second 

 (sarcoptic) form. The punctures made on the skin by these 

 insects give rise to an eruption of small pimples, which at first 

 are of the nature of blisters. When these burst or are broken 

 by friction, a discharge of serum and pus issues from them and 

 keeps the affected parts in a moist condition, which serves to 

 distinguish this kind of mange from sarcoptic mange. The 

 parasites live on the surface of the skin and under the crusts 

 formed by the drying-up of the fliiid from the pimples and by 

 the scaling-off of the scarf-skin. Owing to the irritation caused 

 by the wounds made by the insects and by the animal rubbing 

 himself, the skin becomes thickened, hardened, wrinkled, devoid 

 of hair, and more or less covered with sores. 



2. The insects (sarcoptes) of the second form of mange generally 

 commence their attack on or near the withers, from which they 

 spread over the neck and trunk. Their punctures cause an 

 eruption of small pimples which become filled with serum that 

 soon dries up and forms crusts over the pimples. On this account, 

 when the affected skin is felt by the fingers, during the first stage 

 of the disease, it presents a number of granular eminences. If 

 one of the crusts is scratched off, it will leave a raw spot on the 

 skin about an eighth of an inch in diameter. As the serum 

 contained in the pimples dries up quickly, the skin in this form 

 of mange will present a dry appearance. The scarf-skin more or 

 less scales off, and the hair falls out. In the later stages of the 

 complaint, the skin becomes thickened, rough and wrinkled. 

 Vertical wrinkling of the skin, neck, shoulders, and sides is 

 always present in advanced oases of sarcoptic mange. Each 

 pimple is the result of a pregnant female parasite penetrating, 

 the scarf-skin, and irritating th& underlying sensitive tissues with 



