40(3 



DISEASES OF THE SKIN 



rows of lance-shaped scales on the upper surface of the back. The skin 

 .shows transverse folds and we find four elongated hairs on the posterior 

 end of the body (Fig. 166). 



The male acari and the young parasites generally inhabit cavities 

 in the skin which they have made for themselves 

 (Fig. 167). These cavities are connected extern- 

 ally by short ducts, the entrances of which may be 

 marked by small vesicles or pustules, while the fe- 

 male may move to different parts of the body 

 when sexually ripe, burrowing ducts through the 

 upper layers of the epidermis down as far as the 

 membrana Malpighii, which contains a great deal 

 of fluid. At the end of the duct, that is, the place 

 of entrance of the acari — w^e see the development 

 of a small, somewhat moist nodule, or a vesicle, 

 which dries up ultimately, leaving a scar. This 

 digging of the parasite may produce more or less 

 separation of the epidermis. "We generally find that the parasite has a 

 preference for certain parts of the body, such as the head, neck, abdo- 

 men, and chest, at the root of the tail, and the paws. It is very hard 



Fig. 166. — Female sar- 

 coptes of the dog, magni- 

 fied 75 times, giving the 

 a'jdominal view. {Siedani- 

 grotzky.) 



Fig. 167. — Female sarcoptes burrowing in the skin; also eggs and excrement. 



to detect it with the microscope. The best may is to remove some of the 

 membrane with a scissors or scrape the upper portion of the skin to the 

 corium. If parasites have been present for some time, a secondary 

 eczema is soon developed, which is produced by scratching and rubbing, 

 also by itching of the scabs and scales. This " mange eczema " appears in 

 various forms, according to the sensitiveness of the skin, and is either 

 papular, vesicular, or pustular, and sooner or later produces decided 

 thickness of the skin and leads to the formation of a number of folds, 

 ■wrinkles, and ulcerated points between the clefts of the wrinkles. There 

 is always a certain characteristic appearance about these affected local- 

 ities which makes it easy to distinguish between the parasitic and simple 



