From _anthrax_ it is distinguished by the motility of the bacillus, by its polar sporulation and club shape, by its rounded ends, by its absence from the blood in the earlier stages, by the presence of gas and crepitation in the swellings, and by the deadly action of the infection on Guinea pigs, but not on rabbit, man, nor pigeon. Anthrax is easily inoculable on a cutaneous sore or intravenously whereas emphysematous anthrax is not. _Lesions._ The carcass is liable to be bloated with gas and a reddish, frothy liquid often escapes from mouth nose and anus. Gas is particularly abundant in the substance of the tumor, and the skin covering it may be dry and crackling. An incision made into the swelling exposes a mass of blood extravasation and lymph exudate, the blood predominating in the centre so that it may appear clotted and black, and mixed with gas bubbles, while the yellowish lymph forms the periphery of the tumor, yet streaked more or less with blood, or even pink throughout. The abundance of gas is usually in inverse ratio to the amount of œdema. The muscles beneath or surrounded by an exudate are of a dirty brown or black, and are disintegrated so as to break down readily under pressure of the finger into a blackish pulp. They are infiltrated with gas, crepitate under pressure and assume a golden yellow color on exposure to the air. The gas is comparatively inodorous immediately after death, being mainly carbon dioxide and carbide of hydrogen. Later it may show distinct and even offensive odor, from the formation of hydrogen sulphide, or lactic acid. The muscular fibres are easily teased apart, and show under the microscope masses of blood globules, leucocytes, lymph cells, free nuclei and granules, with, in some points, fatty or waxy degeneration of the fibres, or granular masses that are stained black by osmic acid. The bacillus is present in large numbers, and this with its absence immediately after death from the blood becomes characteristic. The lymph glands near the swelling are usually enlarged and gorged with blood. The lymph plexuses and vessels contain bubbles of gas. The swellings may be subcutaneous, or submucous in the tongue or pharynx, but they occur also in the pleuræ, lungs, heart, pericardium, mediastinum, the peritoneum, the sublumbar connective tissue, and even the walls of the stomach or intestine. It is not uncommon to find a pink effusion into one of the serous membranes. The liver is usually hyperæmic, as may be also the kidneys, but the spleen is rarely enlarged. In this and in the integrity of the blood globules this affection differs from anthrax.