Itch, or SCABIES, a skin disease produced by a minute mite (Sarcoptes scabiei), which burrows in the epidermis of most parts of the body, but especially about the hands. Its presence is marked by a small scaly elevation of the skin, by eruptions as the papillæ of the cutis are perforated, and by the irritating itching sensation.
The mite itself is white or yellowish, broad and flat, with two pairs of mouth parts, and four pairs of appendages. The males are scarcer and much smaller than the females, which are just visible to the naked eye. When they have entered the skin they do not leave it, but form tortuous burrows, through openings in which the embryos escape. The mites are passed by contagion from person to person, either by direct contact or by clothes or bedding. It is probably the embryos or larvæ which are usually thus transmitted. The above species also occurs on the horse, Neapolitan sheep, and lion; S. squamiferus occurs (causing mange) on dogs, pigs, goats, sheep, and apparently also for a short period on man; S. minor is also distinguished on cats and rabbits.
The itch was for a while regarded as a specific disease, the mite being unknown. Avenzoar, an
Arabian physician of the 12th century, is said to have recognised its true nature. So does Scaliger (1557); and Adams figures the animal in a paper read in 1805 before the Royal Society. Amid some scepticism as to the mite during the early part of this century, M. Gales hoaxed the public by figuring as a substitute for the itch-mite the familiar denizen of cheese. His trick was discovered by Raspail, and the existence of a real mite was more distrusted than ever, till in 1834 Renucci, a Corsican student, again demonstrated its presence and characters. It has been often studied since.
The usual cure for itch is found in baths, with abundant soap, or in rubbing with sulphur ointment. If these be not resorted to, the multiplication of the mite may give more serious trouble.
See ARACHNIDA, MITE, PARASITISM, SKIN; Delafond and Bourguignon in Mém. Acad. des Sciences (Paris, 1862); and treatises on Parasites by Leuckart, Küchenmeister, &c.