MANGE. 135 



1. The most common form of mange insect is psoroiytes^ which 

 chiefly- invade those parts that are covered with " horse-hairs," 

 and consequently infest the mane and tail, from which they may 

 spread to the space betw'een 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 out- 

 wards. In this v/ay, 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 con- 

 tagious 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 blisters 

 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 

 which are formed by the drying-up of the fluid from the pimples 

 and by the scaling-off of the scarf-skin. Owing to the irritation 

 caused by the wound;:: 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 (sarco2)tes') 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, during the first stage of the disease, is felt by the 

 fingers, it presents to the touch a number of granular eminences. 

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

 spot about the eighth of an inch in diameter. As the serum con- 

 tained 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 com- 

 plaint, the skin becomes thickened, rough and wrinkled. Vertical 

 wrinkling of the skin, neck, shoulders, and sides is ahvays present 

 in advanced cases of sarcoptic mange. Each pimple is the result 

 of a pregnant female parasite penetrating the scarf-skin, and irri- 

 tating the underlying sensitive tissues wdth her venomous saliva. 

 She then burrow^s underneath the scarf-skin and away from her 

 point of entrance to a distance of about half an inch, so as to form 

 a tunnel or gallery, in which she lays her eggs as she goes along. 

 Consequently, by the time a pimple forms at the inoculated spot, 

 the egg-bearing parasite has left it, and cannot be found if a search 

 be made for her in the pimple, vesicle, or scab. In a white-skinned 

 human subject (affected by itch), the position of the characteristic 



