Abstract
Mice from a colony with subclinical Tyzzer's disease were treated with prednisolone in order to activate a Bacillus piliformis infection. From the livers of these mice the organism was isolated and serially passaged in embryonated eggs. It resisted heating at 75°C for 20 minutes and was still infective after storage at -80°C for 24 days, but not for 52 days or more. Infectivity was maintained for more than a year by storing infectious liver tissue at -190°C. B. piliformis was also isolated from the liver of a mouse with naturally-occurring Tyzzer's disease and maintained for more than 300 passages. Mice inoculated with different egg passages developed fatal Tyzzer's disease and B. piliformis was reisolated from their livers.