What do you mean by burrows?#

Burrows, or _cuniculi_, are tortuous, straight or zigzag, dotted,
slightly elevated, dark-gray or blackish thread-like linear formations,
varying in length from an eighth to a half an inch.

[Illustration: Fig. 76.
Burrow, or cuniculus, greatly magnified. (_After Kaposi._) Showing the
mite, ova, empty shells 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 passage or burrow.

#Upon what parts are burrows most commonly to be found?#

In the interdigital spaces, on the flexor surface of the wrists, about
the mammae in the female, and on the shaft of the penis 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.

[Illustration: 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 classes.

#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.