40 



CIRCULAR 14 8, U. S. DEPARTMENT OF AGRICULTURE 



on the sensitive tissues cause great irritation and itching, and 

 the skin becomes inflamed and swollen, so that small nodules are 

 formed over and around the burrows. As the disease developes vesi- 

 cles are formed which break and discharge serum. As the serum 

 dries, small scabs are formed, and the hair over the affected parts 

 stands erect and some of it drops out. In some cases the affected 

 areas of skin become dry and scurfy, and may have a leatherlike 

 appearance. (Fig. 28.) 



The mechanical injury to the skin resulting from rubbing and 

 biting causes large scabs to form, which adhere firmly to the under- 

 lying tissues. The large scabs often are broken by the movements 



Figure 28. — Sarcoptic mange. Head, neck, and shoulders involved 



of the animal, and blood or serum may stain the scabs a reddish 

 yellow. 



As the disease advances the skin becomes more or less bare in ir- 

 regular-shaped, bald patches, and is greatly thickened and thrown 

 into wrinkles or folds. (Fig. 29.) In severe cases the horse loses 

 flesh rapidly, becomes greatly weakened, and unless properly treated 

 may die. 



Contagiousness. — Sarcoptic mange is transmissible from one spe- 

 cies of animal to another, and also from animals to man. Ordi- 

 narily when one species of animal contracts the contagion from an r 

 other species the mites live only a limited time on the new host. 

 Sarcoptic mites of the sheep, hog, camel, dog, cat, and rabbit may 



