40 CIRCULAR 148, 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 
vellow. 
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- 
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 
