_Causes._ The essential cause of emphysematous anthrax is a rod-shaped germ, variously known as =bacillus anthracis emphysematosa=, =bacillus Chauvæi=, =Rauschbrand bacillus=. This is a rod-shaped microbe, with rounded ends, found singly or connected in pairs, or very short filaments. The bacilli are 3 to 10µ long, by .5µ broad, or when sporulating, 1.1 to 1.3µ. They form spores even in the body of the affected animal, often assuming a club shape by reason of the spore formation near one end. If the spore develops in the center they appear fusiform. They take aniline colors readily, and iodine slightly, assuming in the last case a violet tint. The staining is unaffected by heating in melted balsam. The bacillus grows readily in ordinary culture media, (peptonized gelatine, bouillon, milk, etc.), but, being anærobic, only under the surface in stick cultures, or under a neutral gas or vacuum. It grows most rapidly at a temperature of 36° to 37° C. but also as low as 15° C. The bouillon at 37° C. becomes milky and opaque in 24 hours, and later it clears up, the microbes being precipitated as a free white powder. In gelatine cultures liquefaction takes place in three days, and in twenty days the whole mass may be dissolved and the microbes precipitated to the bottom. Spores may form in the living body and as these are set free by the granular degeneration of the bacilli, the virulent exudate and cultures usually show the microbe in three different forms: 1st; the straight, motile bacillus of one thickness throughout its whole length; 2d; club-shaped or fusiform bacilli, the thickening of the end or median part being due to the endogenous formation of a refrangent spore or spores; and 3d; the free refrangent spores which have been set free by the degeneration and destruction of the sporulating bacilli. The microbe is not found on the surface of the living animal, nor in the blood, for in both the supply of oxygen is too abundant; it forms its colony under the skin, in the tissues, and above all, in the mass of extravasated blood or gelatinoid exudate which its irritation has produced and where air is lacking. The most marked differential features of the microbes of anthrax and emphysematous anthrax are contrasted in the following table:— =Bacillus Anthracis.= =Bacillus of Emphysematous Anthrax.= 5 to 20μ × 1.25μ. 3 to 10μ × 0.5 to 0.6μ. Ends square or cupshaped. Ends rounded. Occurs singly in the living body. Often in pairs or threes in body. Long filaments in cultures. No long filaments. Nonmotile. Motile (sluggishly). Ærobic. Anærobic. No spores formed in living body. Sporulates in living body. Sporulates in air; in surface Sporulates in vacuo; deep in soil. soil.