52 Growth of Bacilli 
slipping group. The observation ceased before general segmentation 
had occurred. 
All the organisms belonging to the slipping group form films under 
suitable conditions. Under unsuitable conditions for film formation 
the larger and stronger members are apt to produce either colonies with 
radiating processes on moderately moist agar or rounded colonies on 
thin, dry agar. The smaller, weaker and slower growing members 
usually produce colonies which to the naked eye look more or less 
rounded. On closer inspection under the microscope, however, most of 
the types of colonies produced by the larger species can be recognised 
on a smaller scale. Exceptionally they produce colonies with long 
processes. B. coli, for example, may form a colony resembling that 
illustrated in Plate V, Fig. 11 (see Hutchinson (1906), Plate I, Fig. 5). 
All the organisms belonging to this group occasionally form long 
unsegmented filaments. 
The mode of growth of the pathogenic anaerobic bacilli, the cocci 
and streptothrices has not yet been investigated, and attempts to follow 
the growth of B. tuberculosis were unsuccessful. 
Summary. 
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. fluorescens , B. 
subtilis and allied organisms and many non-pathogenic species. 
