_Definition._ An acute infectious bacteridian disease manifested by hyperthermia, lameness, and a localized, hot, painful swelling on the shoulder, quarter, leg, neck, trunk or elsewhere, tending to emphysema, and gangrene and when incised showing black extravasated blood, clotted or frothy. This affection was long confounded with anthrax proper, but was differentiated by the observation of Wallraff (1856), Boulit-Josse, Vernant, Pfisterer, Feser, and others and finally Bollinger in 1875 found the motile bacillus. Arloing, Cornevin and Thomas (1879–84) thoroughly substantiated this position, and devised a method of immunizing by inoculation. Feser had however seen the motile sinuous rods in the exudate as early as 1860, and even produced the disease by the inoculation with mud from infected Alpine pastures. _Geographical distribution._ Emphysematous anthrax prevails in limited areas, and particular buildings in Europe, Asia, Africa, Australia and America, and in all climates from the tropics up to the sub-Arctic. It is however most prevalent in spring, summer and autumn. It is not uncommon at the breaking up of the winter snows. It is especially prevalent on damp, undrained land or on such as has dried up in the heats of summer, and has become less prevalent in many localities in connection with drainage and careful cultivation. _Animals susceptible._ The disease is especially common in young cattle, from three months to four years of age. Calves fed on milk are rarely attacked, being in a sense carnivorous and sometimes immunized by toxins from the dam. Cattle over four years usually escape, having already become immune if kept in an infected locality. If brought from a noninfected place they are, at any age, as susceptible as the young. Sheep and goats contract the disease only exceptionally, but like the Guinea pig are easily infected by inoculation. Horses, asses and white rats have only a circumscribed swelling in the seat of inoculation, and foals and buffalo calves sometimes contract it casually. Carnivora and omnivora, (dog, cat, pig, bird, man), and the rabbit are virtually immune. Immune animals may, however, be made to succumb under special treatment. In a rabbit inoculated at the same time with the microbe of black quarter and proteus vulgaris, or micrococcus prodigiosus, or if injected with a little lactic acid, the disease develops promptly and fatally. Over-exertion, producing sarco-lactic acid will also lay the system open to attack. The reduction of the vitality and resistance of the muscle of the rabbit by a contusion, bruise or lacerated wound, or by injecting it with acetic acid, potash salts, alcohol, or common salt, will render the inoculation pathogenic. Again, the introduction of the black quarter microbe into the aqueous humor of the rabbit, where there are so few defensive leucocytes, entails an active proliferation and a fatal result.