44. CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 
and hardening of the skin is characteristic of mange, but the most 
certain diagnosis consists in finding and identifying the mite which 
causes the disease. In the early stages of psoroptic mange the mites 
may usually be found in scrapings taken with a blunt-edged knife 
from around the edges of fresh lesions. In the advanced stages 
scrapings taken from the edges of scabs or from the bottoms of 
the folds of skin may contain mites. 
In the early stages psoroptic mange may be distinguished from 
sarcoptic mange by the character of the lesions and the manner 
of spreading, but the most dependable diagnosis consists in finding 
the mite. For practical purposes where facilities for examination 
are limited the principal differences in form and structure of the 
two species of mites may be summarized thus: The sarcoptic mite 
is slightly smaller than the psoroptic mite, and the body of the 
former is more nearly round than oval. (Fig. 27.) Adults of both 
species have four pairs of legs, those of the psoroptic mites being 
long, and all four pairs extend beyond the margin of the body. 
(Fig. 30.) The sarcoptic mites have shorter legs, and the fourth or 
hind pair and usually the third pair do not extend beyond the 
margin of the body. The head of the common scab mite is tapering 
or cone-shaped and is longer than it is broad, whereas that of the 
psoroptic variety is bluntly rounded in front and is as broad as 
it is long. 
It is advisable to examine several specimens in all cases, because 
under low-power magnifying glasses the females of the two species 
are more easily distinguished from one another than the males. 
On account of the burrowing habits of the sarcoptic mites, they are 
difficult to find, especially in the early stages of the disease. They 
are situated in burrows under conical papille, and by scraping the 
infested area until the blood oozes from the tissue, the mites some- 
times may be found in the scrapings. 
Contagiousness.—Kach species of domesticated animal has its own 
peculiar variety of psoroptic mange, and the variety which lives on 
the horse, ass, or mule is not transmissible to other animals, with the 
possible exception of the camel. The disease is more highly con- 
tagious to all classes of horses than sarcoptic mange. The predis- 
posing causes, manner of spreading, carriers of the mites, and pre- 
cautions to be observed in isolating infected animals and cleaning 
and disinfecting premises are practically the same as for sarcoptic 
mange. 
Treatment.—As the psoroptic mites live on the surface of the skin, 
they are more easily eradicated than the sarcoptic variety. The rem- 
edies recommended for sarcoptic mange are effective in eradicating 
this disease. Two dippings from 10 to 12 days apart may usually 
be depended on to cure ordinary cases. Four or more dippings may 
be necessary in chronic cases. 
CHORIOPTIC MANGE 
CHORIOPTIC MANGE MITE 
Chorioptic or symbiotic scabies, commonly known as foot mange, 
is caused hy a mite (Chorioptes equi) which closely resembles the 
