The bacillus is found on the intestinal mucous membrane, and in the mucus and in advanced stages, in the blood, spleen, liver and kidneys. =Bacillus Coli Communis=, the familiar bacillus of the healthy bowel, is charged by Lignieres with causing a fowl enteritis and probably does so as in mammals when the mucosa has become diseased and non-resistant. At the same time there are so many closely allied forms or varieties of this bacillus found in different intestinal diseases, that it may well be that the pathogenic agent is a modified form or “sport” from the parent microbe, though no clearly defined peculiarities can be established by cultures. The typical colon bacillus is 2 to 3 _μ_ long by 0.4 to 0.6 _μ_ broad, with rounded ends, but it may be ovoid or even round, or it may be 5 _μ_ long. It stains readily with aniline colors, bleaches with iodine. It is ærobic, facultative anærobic, non-motile, non-liquifying, and asporogenous. It ferments all sugars producing gas, acidifies its culture fluids, and coagulates milk. It grows freely at room temperatures in peptonized gelatine, agar and bouillon and on potato. Stab cultures in gelatine have a moss-like tufted appearance. =Pathogenesis.= Injections subcutem, and into the veins and ingestion with food all failed to infect the chicken, while the pigeon died in 24 hours from intravenous injection and in 12 to 18 days from 1 c.c. given subcutem. In rabbits and guinea-pigs hypodermic injection caused abscess, while pleural and peritoneal injections killed in 24 to 48 hours. Rabbits are unaffected by intravenous injection, while guinea-pigs die in 1 to 3 days. =Bacillus of Duck Cholera= found by Cornil and Toupet in the blood of ducks suffering from a diarrhœal enteritis, is 1 to 1.5μ long, by 0.5μ broad, with rounded ends. It is ærobic, non-liquifying, non-motile and asporogenous. Stains in the aniline colors and bleaches in iodine. =Pathogenesis.= In morphology and cultures it resembles the bacillus of fowl cholera, but it fails to infect chicken, pigeon or rabbit. It infects ducks readily by ingestion or hypodermic inoculation. =Spirillum Metchnikowi= was found in 1888, by Gamaleia in the ingesta of chickens dying in Russia of a choleræic enteritis. It resembles the cholera spirillum, but is shorter, broader and more curved. Its size varies, being twice as broad as the cholera spirillum, when found in pigeons. It may be 0.8μ long, by .5μ broad, furnished with one polar flagellum and very motile. It stains in aniline colors and bleaches in iodine. Grows readily in common media at room temperature, and is killed in five minutes by 122° F.; renders milk strongly acid, coagulating it, and perishes in the acid. In eggs turns the albumen yellow and the yolk black. In gelatine it forms transparent colonies and in potato pale brown.