[Biology of a newly isolated agent of the Chlamydia group].

The results of identification of the agent ("Progress" strain) isolated from the organs of a calf sacrificed in the early stage of pneumonia are presented. The agent adapted to yolk sacs of chick embryos was pathogenic for white mice by the intracerebral route and for monkeys infected with aerosol. The infected animals developed specific complement-fixing antibody. The antigen of the agent reacted in the CFT with homologous immune sera and with sera against ornithosis and other members of the ornithosis-lymphogranuloma-trachoma (OLT) group. In cell cultures the agent multiplied well and produced cytoplasmic inclusion bodies characteristic of the OLT group members.