Itch, Or Scabies, a parasitic disease of the skin. There is no doubt that the true character of scabies was known among the ancient Greeks and Romans, but the animal was supposed to be a louse. Avenzoar in the 12th century alluded to its parasitic nature; and Aldrovandus about 1600 gives a good description of the animal, but says it has no legs. Moufet at the same time says it is identical with the mite inhabiting cheese. Occasionally after this we find mention of this parasite in the writings of the great medical fathers, but it was generally forgotten when the grand scientific hoax was played in 1812 by the medical student Gales in Paris, who was cunning enough to substitute a cheese acarus concealed beneath his nail, and thus deceived the judges on the prize offered to the discoverer of the cause of this disease. The Corsican Renucci finally established its reality, taught by the old women of his birthplace, and Raspail gave the first scientific description of the animal in 1839. Since then the best observers of its habits have been Bourguignon, Eichstedt, Schinzinger, and Hebra. - The sar-copte8 hominis, or acarus scaMei, presents three forms. The mature female is discernible by the unaided eye, as a white speck 1/50 of an inch long by 1/75 of an inch broad.

It is white, and resembles in shape a tortoise shell, with an arched back and flat belly. On the back are seen bristles or hairs, and little spines. The skin is tough, and shows irregular transverse parallel rings. There are four pairs of legs, two of which are situated in front and project beyond the anterior, the others toward the posterior end of the body. The two anterior pairs of feet are provided with sucking disks, and with hairs or bristles armed at their extremities with minute claws; the two posterior pairs of feet have no sucking disks, but only long bristles and small claws. The head is bluntly conical, somewhat retractile, and situated between the anterior feet. The mouth consists of a double upper and under lip, between which play the jaws armed with teeth, moving in a horizontal direction up and down, like the blades of scissors over each other, and resembling the claws of a lobster. Eyes are wanting. The male is only half the size of the female, of a blackish color and flattened form. It has sucking disks instead of bristles upon the fourth pair of feet. In other respects it resembles the female. The young, when first hatched, have but three pairs of legs, and in them no distinction of sex is noticeable.

In order to become mature they undergo three separate stages of torpidity, before each of which the body is fat and large in comparison with the extremities. During these they burrow into the skin. By the first process they acquire the wanting pair of legs. When mature the female digs a shallow burrow, and after impregnation ceases to creep over the outer skin, but penetrates deeper and deeper, forming the long holes or "galleries" so well known. The male never enters these galleries where the eggs are found, but digs himself a shallow cell, or seeks new fields for his rambles. The female as she goes on her oblique and downward course deposits her eggs in the gallery, one after the other. The young acarus is hatched about the eighth day, and then emerges from its birthplace to go through the process above described, leaving behind it its broken shell. All stages of development may be seen in these burrows, from the amorphous form in which the eggs are deposited to the perfect young before they break their prison walls. The mother never leaves her hole, and sometimes wanders along for 4 in. beneath the surface; 50 eggs and broken shells are sometimes counted in such burrows.

The whole time required for the young to reach maturity after impregnation is estimated at six weeks. - Infection is produced by the transfer of males and young from one host to another. The sarcoptes loves warmth, and on this account has been called a nocturnal animal, though improperly, for its wanderings are caused by the warmth imparted to the body of its host by lying in a warm bed, by sleeping with another, or by dancing in the evening; and thus it is that they are conveyed from one person to another. It may happen that the female may be scratched out of her burrow, and thus be transplanted to another part of the same host, or to the body of another. Scabies is seldom if ever caught by handling patients, however freely this may be done, from the fact that such examinations take place in cool rooms, when the parasites are quiet. Their favorite lurking places are the tender skin between the fingers, and folds of the axillae; and on infants we find them distributed over the whole surface of the body. They have been cultivated also on the face and scalp, and may inhabit any part of the body.

In persons who suffer from cold hands and feet we often find these parts entirely free from them, while the rest of the body may be covered with the eruption; and the same love of heat is exemplified by the immediate relief which a patient, wrought up to frenzy by the itching of a general scabies at night, finds by jumping out of bed into the cold atmosphere of winter. In order to bore through the epidermis, beneath which it seldom penetrates, the acarus supports itself on its anterior end by means of its hinder legs, and works away with its lobster-like claws. It takes generally 20 or 30 minutes to penetrate the outer layer, but when this has been pierced the progress is more rapid. The poorer in nutriment they find the epidermis the deeper they penetrate, and the greater is the exudation, which lifts up the animal, and causes the white color of the burrow. The young brood seems to require the tender and last formed epidermal layers for its food, and therefore bores further and causes more itching. The long burrows of the females, which cause the real disease, run an irregular course, and become smaller by age as the exudation is absorbed. The entrances generally remain open for the exit of the young and admission of air.

The third or fourth week after inoculation a papular eruption appears; subsequently excoriations, vesicles, pustules, and deposition of pigment show themselves, which are merely the results of scratching, and have no other connection with the parasite than that they are caused by the itching which the animal excites. The same results precisely would follow the same amount of scratching from any other cause. - A peculiar form, known as the Norway itch, consists of conical crusts, sometimes an inch thick, raised on the surface of the skin. This variety affects even the face and nails. Its common occurrence in Norway and rarity elsewhere, only half a dozen cases having been observed in other countries, has led to the supposition that the disease is owing to some other acarus; but Hebra has shown that the crusts consist of dried epithelium and dead acari, and in the few cases in which they have been found present the live animals were identical with the ordinary sarcoptes. This variety leads often to serious complications, as immobility and great swelling of the limbs. Sometimes a circumscribed part of the body is thus affected, while elsewhere it presents the usual appearances of itch.

No satisfactory explanation has yet been offered of its cause, but it yields to treatment as well as the simple sort. - Scabies is found all over the world. In Germany, where the old system of apprenticeship and its attendant wanderings through the land is kept up, and where barracks are filled with dirty soldiery, the disease is borne from one part of the land to another, and thus never dies out. In America it is now comparatively rare, though it occasionally runs through asylums and schools, and thus finds its way into good society. As to treatment, the chief indication is of course to destroy the parasite and its eggs. Little can be said here about the many plans of the present dermatologists; and it is almost unnecessary to say that the use of internal remedies is absurd. Several methods have been advised, called "quick cures," which require but a few hours for their application; but in many cases they fail, and produce an artificial inflammation of the skin. Of course, if any animal or a single egg remain, the disease is not cured. Hundreds of remedies are advised, but the essential agent in its treatment is sulphur. This, in the form of lotious or ointment, and combined with the proper use of baths and potash soaps to soften the skin, will almost always cure in two or three days.

But after the death of the animals and their embryos, much may still remain to be done to remove the eczema, papules, and pustules which they have indirectly caused, and which are to be treated as simple cases of the same disease.

Acarus scabiei, magnified.