(a) The Sarcoptes canis, producing the itch disease, or so-called "mange."

The acarus, when it reaches the skin, burrows in the epidermis, and irritation is excited. Papules or vesicles, or both, appear, partly as the result of this irritation, but chiefly as the result of the rubbing and scratching excited by the irritation The extent of the eruption and the violence of the itching sensation vary according to the number of acari present, and the thickness or delicacy of the skin. From the same causes, a general efflorescence appears in the vicinity of the papules, giving the skin a red appearance, which is best observed where the integument has little colouring matter in its structure.

* See Appendix.

Papulae are especially well marked on those breeds of dogs that have thick and comparatively unirritable skins. Presently, scales form, the hair falls off, the skin becomes infiltrated, thickened, and wrinkled; but there is no exudation on the surface.

In some cases, the papules become vesicles, and these contain a serous fluid, which escapes when the vesicle bursts, and forms yellowish crusts.

Pustules are sometimes met with, and when they burst the contained matter concretes into thick, brownish scales. This is especially the case in domestic favourites, with tender skins and luxurious appetites. The pustules are chiefly located on the inner surface of the thighs, under the abdomen, in the pubic region, etc. In these cases, the skin, is moistened with a serous exudation, having the appearance of drops of sweat.

The common varieties of mange - red, dry, moist - mark the different eruptive conditions of the skin. They all depend on the same cause - the itch parasite, but are immediately and chiefly produced by the vigorous scratching which the itching sensation provokes. Whether the eruption be a simple efflorescence, or papular, or vescicular, or pustular, will depend partly on the state of health of the animal, partly on the sensibility of the integument, and partly on the duration of the disease. Hence the external features of confirmed and developed mange vary according to circumstances; but in all such cases, the hair drops off, the thickened skin - known to be thickened by pinching up a fold between the finger and the thumb - is thrown into wrinkles, especially about the head and on the back, and disfigured by scabs, chaps, and fissures. On some parts, small red points of clotted blood will be observed.

All parts of the body may be invaded with mange, but it generally manifests itself first about the back, the nose, the ears, and the eyebrows. In five or six weeks, so rapidly does the disease spread, that the whole body may be mangy; and in bad or neglected cases, the dog sinks into a state of incurable cachexia.

The itching is the most distressing symptom; slight at first when the acari are few and the irritation caused by their presence in the skin is bearable, but gradually increasing with the rapid multiplication of the parasites. The itchy sensation is at first confined to the spots where the acari are deposited, and are engaged in channeling the epidermis; but subsequently the sensory nerves of the skin convey the sensation of universal itching, and the wretched animal spends his days and nights in rubbing, scratching, and nibbling himself.

(b) The other form of itch, or parasitic mange, is due to the presence of the Demodex folliculorum in the sebaceous and hair follicles.

This acarus sets up a slight circumscribed swelling of the skin, attended with a little increase of temperature and redness. Numerous small pimply tumours, due to inflammation of the follicles, make their appearance; and fluid, at first serous, subsequently purulent, exudes from, or can be squeezed out of, these swellings. The skin is after this covered with minute pustules; the exuded matter hardens into scabs, and the skin is thickened and chapped as in the preceding form of mange. The hair drops off. The itching is neither very vehement nor frequent.

The presence of this parasite in the hair follicles may be proved by placing an extracted hair-bulb under the microscope, when the demodex will be seen. The hair which falls off is never restored, as the follicle is destroyed by the inflammation and suppuration of its lining membrane.

Diet, confinement, and ill-health predispose the dog to become affected with mange.

It is highly contagious. It is a matter of common observation that some healthy dogs do not catch what is supposed to be true mange, even when they sleep with so-called mangy dogs - that other dogs become affected only after repeated and long-continued contact - and that others, again, become mangy in a few hours. In the first case, the disease is probably eczema, which resembles the mangy parasitic eruption in rough detail; in the second case, the disease is due to the demodex, whose habits, structure, and habitat prevent it from rapidly passing from one body to another; whereas, in the third case, the adult or larval acari, lying superficially or moving about nimbly, easily transpose themselves, or get transposed.

Some writers speak of the hereditary nature of mange. It is obvious that true mange has no such character; it cannot be transmitted from parent to offspring, and cannot be produced except by an animal parasite external to the patient.

When mange breaks out on a domestic favourite, the unpleasant fact should be remembered, that the disease is communicable to man by the transmigration of the parasite.

As in man, so in the dog, skin diseases may be caused, not only by animal, but by vegetable parasites. In the dog, this important subject requires further investigation; but there appears to be no doubt that a form of "mange," most frequent in young puppies, and characterized by depilation, furfuraceous scales, and slight scratching, is due to the presence of such a growth.

Treatment

The object is to kill the parasites. First, wash the whole body thoroughly with soft soap and warm water; then dry the skin and hair; and, lastly, rub in Benzine. These applications may have to be repeated more than once; but one thorough application is generally sufficient as far as the destruction of the acari is concerned, and the remaining eruptions usually disappear without any treatment. Sulphur ointment is another good remedy; washing being used as directed. The whole body should be subjected to these processes at the same time, because if one parasite escapes destruction, others will soon be bred. The bedding, etc., should be destroyed; and the dog, after having been thoroughly dressed, should be provided with a new place to lie on.

In some cases it may be necessary to give internal remedies; the treatment of eczema should then be referred to.