_Animals susceptible._ It is pathogenic to deer, buffalo, cattle, horses, swine, rabbits, rats, mice, and to a lesser extent to goats and sheep. The _pathogenesis_ varies with the immediate source of the microbe. When obtained from cattle a drop of blood kills rabbits in twelve to twenty hours, with intense hæmorrhagic laryngitis and tracheitis. Guinea pigs die in forty to eighty hours. When obtained from the buffalo it killed horse, ox, or pig in twenty to forty-eight hours. That obtained from barbone (buffalo) appears to be more potent than that from septicæmia hæmorrhagica (cattle). _Vitality of the microbe._ Simple drying destroys virulence in six to twenty-two days. Virulence is retained for nine days in putrid flesh. It is preserved, and the microbe multiplies in soil or water containing organic matter and nitrates. It is easily destroyed by ordinary antiseptics 1:5000 of mercuric chloride destroying its vitality in one minute (Hueppe). On the contrary it shows a great resistance to changes of temperature. It grows in the soil at 55° to 60° F. (Hueppe), and in old cultures may resist for an hour a temperature of 175° to 195° (Oreste and Armanni). _Accessory Causes._ These are such conditions as favor transmission of, or receptivity to the microbe. In Southern France the disease is most common in the winter months, probably because the soil water rises then; on the Roman marshes on the other hand, it prevails especially from May to October, when the water is lowest and most impure. In New York I have seen it especially at the breaking up of the winter frosts, when the water, pent up in the rich organic soils, is suddenly released. It is pre-eminently the disease of wet soils, rich in the debris of decomposing organic matter, of the rich prairies and bottom lands of the Mississippi Valley, of springy, swampy or mucky soils elsewhere, of the Pontine marshes at Rome, of the Delta of the Nile, of the rich virgin soils in Asia. Youth has the greatest receptivity, the older animals having probably acquired immunity through an earlier attack. The animals that live in herds infect each other by contact, fighting, licking, etc., others are affected by eating the vegetation or drinking the water soiled by the diseased, wild boars by eating the carcasses, and all animals by the attacks of biting or blood-sucking insects which have just come from the diseased. It is claimed that the infection is carried by men and animals, and by the sale in villages of the flesh of infected animals. Dogs, wolves, foxes, and other carnivorous animals and birds will also carry the infection for long distances. Finally, it will travel to a greater or lesser distance with running water.