The Division and Post-fission Movements of Bacilli when Grown on Solid Media

Abstract

1. All the bacilli hitherto investigated, when growing on the surface or in the depth of agar, exhibit “post-fission” movements after division.2. Four types of post-fission movement have been noticed, which may be termed “loop-forming,” “folding,” “snapping” and “slipping.”3. These types of post-fission movement seem to depend on the strength, adherence and mode of rupture of the capsule. In the “loop-forming” group the capsule is very strong and adherent and is very seldom ruptured. In the “folding” group the portion of the capsule uniting the adjacent bacilli in the chain is long and flexible. In the “snapping-group” the capsule seems to undergo partial rupture at the time of division, and in the “slipping” group it is completely ruptured.4. “Loop-forming” post-fission movements are shown by B. anthracis, “folding” by B. pestis and certain organisms morphologically resembling B. anthracis, “snapping” by all diphtheroid organisms and “slipping” by organisms belonging to the typhoid-enteritidis-colon group, vibrios, the butter bacillus (Rabinowitch), B. pyocyaneus, B. fiuorescens, B. subtilis and allied organisms and many non-pathogenic species.5. The characters of the colonies formed by organisms exhibiting loop-forming, folding and snapping post-fission movements are not markedly altered by the condition of medium under ordinary conditions of cultivation. When thickly sown on moist agar continuous growths are formed by all of them, but the edges of these growths resemble the edges of the separate colonies. All organisms exhibiting slipping post-fission movements form films on moist agar. Under unsuitable conditions for film formation the larger and stronger members produce either colonies with radiating processes on moderately moist agar, or rounded colonies on dry agar. The smaller, weaker, and slower growing members produce colonies which to the naked eye appear more or less rounded.