The organism develops large, terminal spores, which are at first oval,
but when fully developed are perfectly round and measure from 1.5 to 2
μ in diameter.
Spores develop rapidly in the egg-pork medium at 20° to 25° C., fully
developed spores being noted in from five to seven days. At ice-box
temperature (8° to 10° C.) partly developed spores were noted in the
egg-pork medium at 10 days and fully developed spores at 2 weeks.
Occasional spores were noted in old agar and gelatin cultures, but
abundant spore formation was seen only in the egg-pork medium. No
spores were noted in bouillon cultures, even at 10 weeks.