_Accessory Causes._ Birds sent to poultry shows will often contract the disease and introduce it into the home flock on their return. It may also be imported in newly purchased birds, or on eggs obtained for hatching. It is even alleged that it has been propagated by feeding healthy hens on the eggs of diseased ones. When chickens run at large it passes easily from flock to flock in the immediate vicinity. The infected manure is, however, the most common channel of infection. Carried on the feet or bill this contaminates the food and drinking water, and washed into streams and ponds, it finally in any case reaches the alimentary canal of the susceptible bird. Or drying up and raised as dust it is inhaled into the lungs. Or finally from any such source it infects any open sore. As granivorous birds, wild and tame, suffer from fowl cholera, it is often introduced by the wild, especially coming from infected poultry yards. Predatory birds, like hawks and buzzards, but the latter especially, are common bearers of infection. Rabbits, which contract the affection so readily, transmit it equally with birds, but man or beast, soiled by the manure will convey it. Insects are among the most prolific bearers, hence, as noted by Salmon, the infection may fail to overstep a close fence in winter, but is subject to no such limitation during the fly season. In this respect chicken cholera agrees with Asiatic cholera, typhoid fever and other affections in which the virus abounds in the alvine discharges. The sale and transportation of the guano from the infected poultry yard is a direct cause of new outbreaks. Feeding on the carcasses or offal of the infected birds is a further cause. It must not be forgotten that the microbe is largely saprophytic, living indefinitely in the organic matter in soils, and determining new outbreaks when brought in contact with susceptible animals. Thus a period of immunity may be followed by infection when new birds are brought in or when young and susceptible ones grow up. _Susceptible Animals._ Fowl cholera is preëminently a disease of chickens, but the microbe is successfully transferred to pigeons, peafowl, pheasants, parrots, ducks, canaries, sparrows and other small birds, also to Guinea pigs, rabbits, white and gray mice. Guinea pigs have abscesses in the seats of inoculation (Pasteur); the same is alleged of sheep and horses (Kitt), and man (Marchiafava, Celli). Injection into a cow’s teat caused chronic catarrhal mammitis in which the microbe persisted for a long while (Kitt). Like other members of the group of microbes causing septicæmia hæmorrhagica, the pathogeny and even the morphology are liable to material modification as grown in different environment (genera). Some of the forms of cholera occurring among domesticated birds and held to be distinct diseases may find in this an explanation. Rabieaux claims that under favorable conditions it has been transmitted to the frog.