ITCH-MITE, Acarus scald, or sareoptes scabiei, is supposed by some naturalists to have been referred to by Aristotle in the 5th book of his Ilistoria A.nimaliam, cap. 31. But although the itch was undoubtedly known both to the Greeks and Romans, there is no certain evidence that a mite was recognized as the cause of the disease earlier than by Avenzoar, an Arabian physician of the 12th century. Throughout the whole of the middle ages, and till the present century, the necessary connection between the ease and the mite was universally recognized, as is obvious from the writings of ger (1557) and others; and a paper read by Adams before the royal society in 1805, con tains two very good figures of the mite. During the first ten years of this century, many practitioners, not succeeding in finding the animal, expressed doubts concerning its existence, and in 1812 there occurred a remarkable incident in the history of this mite. M. Gales, the chief apothecary to the hospital of St. Louis, tempted by a prize offered by one of the unbelievers, published in that year a treatise on the itch, in which he declared that he had seen more than 300 of the mites, and in which he gave a draw ing of the animal, which, although it differed materially from the delineations of earlier observers, was at once accepted as an exact representation of the true parasite, and was copied for several years into all works treating the itch, until Easpail discovered that M. Gales's memoir was a tissue of d"ceptions, and that the animal which he had figured was the cheese-mite! The existence of the itch-mile was now more distrusted than ever, until,•in 1834, Itenucci, a Corsican student, demonstrated the presence of the creature: Many points regarding the structure and habits of this curious animal have been since revealed by the investigations of Gras, Raspail, Debra, Glidden, and especially De la Fond and Bourguignon, who have presented to the French institute A P1? effect Treat ise on the Entomology and Comparative Pathology of the Itch as it occurs in Nan and the Domestic Animals, which has been published in the last volume (1862) of the Memoires presentgs par divers Savants a l'Acadeatie des Sciences.
The adult female mite is considerably larger than the male; it is visible to the naked eye, and forms a roundish grayish-white corpuscle, not unlike a starch granule; it is about one-fifth of a line in length, and one-seventh in breadth. When seen under the microscope,
it presents a truncated tortoise-like shape, and is seen to be studded with hairs and bris tles. The head termivates in two pairs of mandibles, and these mandibles afford good characteristic distinctions of the species.
In order to penetrate the horny layer of the epidermis, the mite assumes, according to Glidden, a nearly perpendicular position; and to avoid as much trouble as possible, it usually selects such spots as give least resistance, such as the space between the fingers, the inside of the wrist, etc. Once fairly buried, it does not again come out, but burrows, and forms tortuous galleries within the skin. These galleries resemble the mark which is formed when a pen is drawn lightly over the skin without causing a scratch. In young children. and in persons with a delicate skin, they appear of a gray-. ish-white color; while in persons with a coarse dirty skin they are of a blackish tint: At certain intervals, the galleries are pierced by small openings, for the admission of air; it is through these openings, which sometimes appear like very minute black dots, that the young escape. The vesicles characteristic of the itch-disease arc attributed to a poison ejected by the mite. The males arc smaller and much scarcer than the', females.
There are numerous species of itch-mite (scrcoptes) which infest the lower animals-. One of them (S. cant's) produces mange (q.v.) in dogs; another (S. qui), a comparatively large species, sometimes occurs in. horses; another (S. bovis) in oxen in some parts of Europe; another (S. ocis) in sheep. Some of these are occasionally transferred to burnaut. beings, and cause irritation and annoyance, which, however, seems to be limited to the life of the individual mites transferred, the situation not being congenial enough for their increase.
For further information on the structure and habits of this animal, the reader is referred to the second volume of Kilehenmeister's work on parasites (translated for the Sydenham society), and to Bourguignon's treatise.