[Ill.u.s.tration: Fig. 76.

Burrow, or cuniculus, greatly magnified. (_After Kaposi._) Showing the mite, ova, empty sh.e.l.ls and excrement.]

How is a burrow formed?

By the impregnated female parasite, which penetrates the epidermis obliquely to the rete, depositing as it goes along ten or fifteen ova, forming a minute pa.s.sage or burrow.

Upon what parts are burrows most commonly to be found?

In the interdigital s.p.a.ces, on the flexor surface of the wrists, about the mammae in the female, and on the shaft of the p.e.n.i.s in the male.

Are burrows usually present in numbers?

No. Several may be found in a single case, but they are rarely numerous, as the irritation caused by the penetration of the parasites leads either to violent scratching and their destruction, or gives rise to the formation of vesicles and pustules, and consequently their formation is prevented.

What course does scabies pursue?

Chronic and progressive, showing no tendency to spontaneous disappearance.

To what is scabies due?

To the invasion of the cutaneous structures by an animal parasite, the sarcoptes scabiei (_acarus scabiei_). The male mite is never found in the skin and apparently takes no direct part in the production of the symptoms.

[Ill.u.s.tration: Fig. 77. Fig. 78.

Sarcoptes scabiei x 100.

(_After Duhring._) Female. Ventral surface. Male.]

The disease is contagious to a marked degree, and is most commonly contracted by sleeping with those affected, or by occupying a bed in which an affected person has slept. It occurs, for obvious reasons, usually among the poor, although it is now quite frequently met with among the better cla.s.ses.

State the diagnostic features of scabies.

The burrows, the peculiar distribution and the multiformity of the eruption, the progressive development, and usually a history of contagion.

How do vesicular and pustular eczema differ from scabies?

Eczema is usually limited in extent, or irregularly distributed, is distinctly patchy, with often the formation of large diffused areas; it is variable in its clinical behavior, better and worse from time to time, and differs, moreover, in the absence of burrows and of a history of contagion.

How does pediculosis corporis differ from scabies?

In the distribution of the eruption. The pediculi live in the clothing and go to the skin solely for nourishment, and hence the eruption in that condition is upon covered parts, especially those parts with which the clothing lies closely in contact, as around the neck, across the upper part of the back, about the waist and down the outside of the thighs; _the hands are free_.

State the prognosis of scabies.

It is favorable. The disease is readily cured, and, as soon as the parasites and their ova are destroyed, the itching and the secondary symptoms, as a rule, rapidly disappear.

How is scabies treated?

Treatment is entirely external, and consists of a preliminary soap-and-hot-water bath, an application, twice daily for three days, of a remedy destructive to the parasites and ova, and finally another bath.

Inquiry as to others of the family should be made, and, if affected, treated at the same time. The wearing apparel should be looked after--boiled, baked, or sulphur-fumigated.

What remedial applications are employed in scabies?

Sulphur, balsam of Peru, styrax, and [beta]-naphthol, singly or severally combined. In children, or in those of sensitive skin, the following:--

[Rx] Sulphur. praecip., .................... [dram]iv Balsam. Peruv., ...................... [dram]ij Adipis, Petrolati, ......... [=a][=a] ........ [Oz]iss. M.

And in adults, or those of non-irritable skin:--

[Rx] Sulphur, praecip., .................... [Oz]j Balsam. Peruv., ...................... [Oz]ss [beta]-Naphthol, ..................... [dram]ij Adipis, Petrolati, ... [=a][=a] ... q.s. ad .. [Oz]iv. M.

Styrax is a remedy of value and is commonly employed as an ointment in the strength of one part to two or three parts of lard.

Is one such course of treatment sufficient to bring about a cure?

Yes, in ordinary cases, if the applications have been carefully and thoroughly made; exceptionally, however, some parasites and ova escape destruction, and consequently itching will again begin to show itself at the end of a week or ten days, and a repet.i.tion of the treatment become necessary.

Does the secondary dermat.i.tis which is always present in severe cases require treatment?

Only when it is unusually persistent or severe; in such cases the various soothing applications, lotions or ointments employed in acute eczema are to be prescribed.

Is a dermat.i.tis due to too active and prolonged treatment ever mistaken for persistence of the scabies?

Yes.

Pediculosis.

(_Synonyms:_ Phtheiriasis; Lousiness.)

Define pediculosis.

Pediculosis is a term applied to that condition of local or general cutaneous irritation due to the presence of the animal parasite, the pediculus, or louse.