46 
Growth of Bacilli 
deep, is due to the strength, close application and non-liability to 
rupture of the capsule covering the chains ; in the “ folding ” group to 
its length and flexibility between the bacilli composing the chains; in 
the “snapping” group to its incomplete rupture during division and 
the persistence of this condition subsequently; and in the “ slipping ” 
group to its complete rupture at the time of division. 
The fully formed colonies produced by certain members of the 
“ folding ” group may be at times somewhat difficult to distinguish from 
anthrax colonies. This is due to the fact that in both cases wavy 
strands composed of numerous parallel chains of bacilli compose the 
central portions of the colonies. Under a lens both consequently have 
a “ cracked ice ” appearance. Usually the margins of the colonies of 
the folding group are thick and wavy being formed of strands similar 
in structure to those which compose the centre. More rarely a thin 
expansion of irregular loops may be seen (Plate V, Fig. 10). On the 
other hand anthrax colonies almost invariably possess thinner margins, 
composed of well formed loops, and very frequently exhibit outgrowths 
of the type shown in Plate IV, Fig. 13. The terminal portions of the 
chain, with their secondary systems of loops (Plate III, Fig. 7), may also 
often be found. 
More rarely colonies, somewhat resembling anthrax colonies, may be 
produced by members of the subtilis group (slipping group). These 
are only formed when long unsegmented filaments are being produced, 
which necessarily behave for mechanical reasons in the same way as 
anthrax chains (see Diagram 14). 
The colonies of bacilli. 
During the progress of the observations which have just been 
described, some attempts were made to ascertain to what extent the 
mode of “post-fission” movement influenced the appeai’ance of surface 
colonies, under ordinary conditions of cultivation. For the purposes 
of diagnosis and investigation considerable importance is necessarily 
attached to the appearance of surface colonies, owing to the aid it 
renders in picking out the suspected organisms in mixed cultures. It 
is of interest therefore to know to what extent the colonies produced 
by a given organism are capable of variation. Making use of the same 
batch of agar under constant conditions of incubation the factor which 
was found to influence to the greatest degree the forms assumed by the 
colonies was the dryness of the medium. 
