$10,000,000 to $25,000,000, per annum. _Bacteriology._ Prior to 1885 bacteria had been found in the different outbreaks of contagious fevers in swine, and the bacillus of swine erysipelas had been demonstrated in 1882, but it was only two years later (1884) that the motile bacillus choleræ suis was first described by Klein, and in 1885 that Salmon and Smith demonstrated it as the essential cause of the disease, together with its biological and cultural peculiarities. It is a short bacillus, 1.2 to 2μ × 0.5 to 0.8μ, but varying considerably in size according to the stage of its growth and the genera of animal or culture medium in which it is grown. It has rounded ends and is usually in pairs connected by an invisible band. It stains promptly in all the aqueous aniline colors, but loses the stain in a solution of iodine (Gram’s). Prolonged exposure of artificial cultures produces an uniform stain, while a transient exposure, and especially of bacilli obtained from the tissues, stains them most deeply at the ends (polar) and periphery, while the centre remains somewhat clear. This is less marked than in the bacillus of swine plague, yet serves to show the relation between this microbe and the colon group. It is _ærobic_ (facultative anærobic), non-liquefying, and, in fluids, very actively motile, the movements lasting for months in preserved specimens (Smith). It grows luxuriantly in various culture media, and especially in alkaline ones, at the room temperature, and most actively at 85° to 100° F. It may grow as low as 60° to 70° F. and as high as 104°. (Swine plague bacillus grows at 55.4°). On _peptonized gelatine_ the surface colonies are usually round and flattened, those in its substance globular and smaller, and those at the bottom expanded next the glass and rising in the center into the gelatine like a knob. At 48 hours they appear as opaque whitish points and slowly increase to ½ to 2 mm. They may be brown by transmitted light, the depth of color increasing with age. On _agar_ the colonies are grayish, shining and translucent and may reach the size of 4 to 6 mm. On _potato_ (alkaline) a straw yellow film is formed, darkening with growth. In _bouillon_ a turbidity appears in 24 hours, and in 1 or 2 weeks a precipitate and surface film. The bacillus is usually larger in the gelatine and smaller in the bouillon than it is in the tissues. It seems to produce neither phenol nor indol. Its behavior with sugars is significant. It ferments glucose producing acid and gas; does not ferment saccharose nor lactose, but turns the saccharose solution alkaline (no gas). In bouillon containing muscle glucose, it may without additional glucose form a little gas. The swine plague bacillus ferments saccharose producing acids but no gas: it ferments neither glucose nor lactose but turns the former acid. Milk is neither coagulated nor soured by the hog cholera bacillus, but in 3 to 4 weeks it undergoes a change, becoming saponified.