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 subcutaneous tissue and altered blood, forms (Fig. 29).  Meanwhile the induration extends, fresh vesicles form and in turn burst, and the eschar increases in size.  The neighbouring lymph glands soon become swollen and tender.  The affected part is hot and itchy, but the patient does not complain of great pain.  There is a moderate degree of constitutional disturbance, with headache, nausea, and sometimes shivering.

If the infection becomes generalised—­anthracaemia—­the temperature rises to 103 or 104 F., the pulse becomes feeble and rapid, and other signs of severe blood-poisoning appear:  vomiting, diarrhoea, pains in the limbs, headache and delirium, and the condition proves fatal in from five to eight days.

Differential Diagnosis.—­When the malignant pustule is fully developed, the central slough with the surrounding vesicles and the widespread oedema are characteristic.  The bacillus can be obtained from the peripheral portion of the slough, from the blisters, and from the adjacent lymph vessels and glands.  The occupation of the patient may suggest the possibility of anthrax infection.

[Illustration:  FIG. 28.—­Malignant Pustule, third day after infection with Anthrax, showing great oedema of upper extremity and pectoral region (cf.  Fig. 29).]

[Illustration:  FIG. 29.—­Malignant Pustule, fourteen days after infection, showing black eschar in process of separation.  The oedema has largely disappeared.  Treated by Sclavo’s serum (cf.  Fig. 28).]

Prophylaxis.—­Any wound suspected of being infected with anthrax should at once be cauterised with caustic potash, the actual cautery, or pure carbolic acid.

Treatment.—­The best results hitherto obtained have followed the use of the anti-anthrax serum introduced by Sclavo.  The initial dose is 40 c.c., and if the serum is given early in the disease, the beneficial effects are manifest in a few hours.  Favourable results have also followed the use of pyocyanase, a vaccine prepared from the bacillus pyocyaneus.