Definition And Description

Scabies is a zooparasitic disease, produced by the lodgment and increase of certain minute insects on and under the skin. It is usually characterized by the appearance of little transparent, isolated, non-umbilicated vesicles upon the skin, especially between the fingers and on other parts of the hands. The development of these vest-cles is accompanied with itching, usually worse at night. The pruritus leads to scratching, and this scratching of the diseased parts and scratching or handling of other portions of the integument, leads to the extension of the disease to them, and we find that, as a rule, the affection next invades the penis in the male, the breasts in women, and the feet in children, from which parts it may extend to all other portions of the surface - the anterior, however, in preference to the posterior. The head and face are rarely if ever affected.

After a few days, in some cases, later in others, additional phenomena are presented. These, as a rule, are papular, and pustular forms of eczema, in those predisposed to this affection, together with scratch-marks and rather large, isolated, and commonly umbilicated pustules. In those possessing a decidedly pyogenic constitution, furuncles and abscesses may appear. In other words, the eruption in advanced cases is frequently polymorphous.

These are the lesions visible on a cursory examination, but none of them are absolutely diagnostic, although the vesicles first alluded to are not, so far as I am aware, met with in any other affection. There is, however, another lesion that is pathognomonic, and which, if detected, leaves no doubt as to the nature of the affection. I allude to what is called the caniculus, or burrow, made by the insect that causes the disease. This lesion is a fine line, more frequently curved than straight, and of a whitish or grayish color, sometimes interrupted with black points. The line is usually from one-fourth to one-half inch in length, and can be de-tected only by close inspection, but more easily with the aid of a lens. It is usually found near the vesicles, sometimes upon their surface, but occasionally is at a distance from them.

Pruritus is almost an invariable accompaniment, and may be mild, but is usually worse at night, when the patient is warm in bed.

Etiology

Scabies is caused by the presence of an insect called the Acarus Scabiei, Or Sarcoptis Hominis

This proposition, which I presume none would dispute at the present day, in reality touches on a curious phase in medical history, exhibiting, as it does, the intense conservatism of the medical profession, and its, sometimes, dogged resistance to the reception of new truths. The connection between Scabies and the insect just referred to, was noticed by Avenzoar in the twelfth century. He speaks of the affection as due to small animals which "sunt pedicilli subter manum, crurum et pedum cittern ser-pentcs, et pustulas ibidem excitantes, aqua plenas; tam parva an animalcula,, quam vix visu discemi valeant.* This statement, made nearly 700 years ago, and reiterated by other careful observers, was not accepted by the mass of the profession as true, until within the last fifty years. Turner,+ the author of the first English work devoted to skin diseases, alludes to the matter as follows: "Of Lice there are reckoned four Kinds, troublesome to the Bodies of Men." After speaking of the head-louse, body-louse, and crab-louse, he says the fourth kind "are those generated (according to some) under the Cuticle, being found on the Hands and Feet, of a round Form like the small Eggs of Butter-Flyes, some of them so minute as to escape the Sight, altho' by their creeping under the Scarf-Skin they often Stir up a most intolerable Itching, and sometimes break forth and discover themselves, altho' for the most Part they lye hid and conceal themselves; Some Authors mention them and treat of them as I suppose, under the names of Acari, Cyrones and Pediculi."

Bonomio also, in 1687, announced the existence of these insects. Not having access to the original statements of Bonomio, I am forced to quote the account of his discoveries from a later writer.* I do so the more willingly as the description, for accuracy and vividness, could hardly be improved on at the present day. Baker says: "The Microscope has discovered, what without it could scarce have been imagined, that the Distemper we call the Itch, is owing to little insects under the Cuticula, whose continual Bitings cause an ouzing of Serum from the Cutis, and produce those Pustules or watry Bladders whereby this Disease is known. This was found out by Dr. Bonomio, who observing that itchy People frequently pull out of their scabby Skin little Bladders of Water, with the Point of a Pin, and crack them on their Nails like Fleas, he determined to examie what these Bladders might really be. Wherefore picking out with a fine Needle a little Pustule from a Place scabbed over, or where there was a severe Itching, he squeezed a thin matter from it and perceived a very small white Globule scarcely discernable, which, applying to the Microscope, he found to be a very minute Animal, in Shape resembling a Tortoise, of a whitish Colour, but darker on the Back than elsewhere, with long and thick Hairs issuing from it, very nimble in its motion, having six Legs,+ and two little Horns.

* I quota from a Latin translation of his work.

+ A Treatise of Diseases Incident to the Skin, p. 150. London, 1714.

This Experiment was repeated on itchy Persons of all Ages, Sexes and Complexions, and at all Seasons of the Year, and he constantly found the same Animalcules in most of the watery Pustules; and though by reason of their Minuteness and Colour (which is the same as that of the Skin) it is difficult to discern these Creatures on the Surface of the Body, yet he sometimes saw them upon the joints of the Fingers in the little Furrows of the Cuticula, where they first begin to enter with their sharp Heads, gnawing and working in their Bodies, till they are got quite under the Cuticula, where they burrow from Place to Place, cause a troublesome and grievous Itching, and force the infected Person to scratch, which only serves to increase the malady; for, by breaking the little Pustules, and some small Blood-vessels, Scabs, crusty Sores, and such like foul Symptoms ensue; whilst the mischievous Animalcules escape the nails by their minuteness, and disperse themselves the farther."