hey remain viable in the dry state for long periods, even up to
a year, but they survive boiling for five minutes, and must be subjected
to dry heat at 140 C. for several hours before they are destroyed.

[Illustration: FIG. 27.--Bacillus of Anthrax in section of skin, from a
case of malignant pustule; shows vesicle containing bacilli. x 400 diam.
Gram's stain.]

_Clinical Varieties of Anthrax._--In man, anthrax may manifest itself in
one of three clinical forms.

It may be transmitted by means of spores or bacilli directly from a
diseased animal to those who, by their occupation or otherwise, are
brought into contact with it--for example, shepherds, butchers,
veterinary surgeons, or hide-porters. Infection may occur on the face by
the use of a shaving-brush contaminated by spores. The path of infection
is usually through an abrasion of the skin, and the primary
manifestations are local, constituting what is known as _the malignant
pustule_.

In other cases the disease is contracted through the inhalation of the
dried spores into the respiratory passages. This occurs oftenest in
those who work amongst wool, fur, and rags, and a form of acute
pneumonia of great virulence ensues. This affection is known as
_wool-sorter's disease_, and is almost universally fatal.

There is reason to believe that infection may also take place by means
of spores ingested into the alimentary canal in meat or milk derived
from diseased animals, or in infected water.

#Clinical Features of Malignant Pustule.#--We shall here confine
ourselves to the consideration of the local lesion as it occurs in the
skin--_the malignant pustule_.

The point of infection is usually on an uncovered part of the body, such
as the face, hands, arms, or back of the neck, and the wound may be
exceedingly minute. After an incubation period varying from a few hours
to several days, a reddish nodule resembling a small boil appears at the
seat of inoculation, the immediately surrounding skin becomes swollen
and indurated, and over the indurated area there appear a number of
small vesicles containing serum, which at first is clear but soon
becomes blood-stained (Fig. 28). Coincidently the subcutaneous tissue
for a considerable distance around becomes markedly oedematous, and the
skin red and tense. Within a few hours, blood is extravasated in the
centre of the indurated area, the blisters burst, and a dark brown or
black eschar, composed of necrosed skin and sub