1. Strains of-P. avicida from "spontaneous epidemics" of fowl cholera, when introduced intranasally in fixed doses into specially bred chickens, induced fatal fowl cholera in about 40 per cent but did not survive in the nasal clefts of resistant birds nor spread to normal contacts.
2. Strains of P. avicida from "spontaneous endemics" of fowl cholera, when introduced similarly into chickens, failed to kill but did survive in the nasal clefts of inoculated birds and spread readily to normal contacts.
3. "Laboratory" variants of the epidemic strains of P. avicida failed to kill or survive in the test birds and did not spread to contacts.