G. S. Graham-Smith 
43 
Irregularities due to extreme rapidity of growth or to the formation 
of long unsegmented threads may occur, but are seldom met with in 
cultures of the smaller bacilli belonging to this group. In the former 
case “ the rods may grow so fast after separation that instead of 
ultimately lying side by side the impinging of one upon the other near 
the proximal end of the latter carries this latter in front of it, and 
swings it round so that it lies right across and in front of the axis of 
the first, forming an irregular T.” Irregularities due to this cause are not 
very common in surface cultures. A more common and more important 
cause of irregularity of growth, which is more especially apt to be a 
disturbing factor in the case of large, relatively strong, bacilli of the 
subtilis group, is due to the formation of long unsegmented threads. Very 
frequently the gradual increase in length in such threads causes them to 
develop primary and secondary loops, such as occur in surface cultures 
of B. anthracis. Ultimately however segmentation usually occurs and 
owing to the bacilli composing the loop slipping past each other an 
irregular network is produced. 
Diagram 12, series A, illustrates the formation of long parallel 
partially segmented threads in a culture of an organism belonging to 
the subtilis group, and series B illustrates the changes which occur in 
a loop developed from such parallel threads. In series B, Fig. 1 a 
well formed loop is seen, and in Figs. 2, 3 and 4 the gradual develop¬ 
ment of secondary loops. In the latter figure however slipping has 
already commenced at a. In Fig. 5 the secondary loop on the left is 
still better marked, but the primary loop is beginning to break up by 
segmentation (b, b, b, b) of the threads composing it. Fig. 6 shows 
the irregular network resulting from the breaking up of the loop by 
segmentation and slipping. 
This series also illustrates another irregular post-fission movement 
which is not infrequently seen in preparations of some strong film 
forming organisms. Instead of slipping past each other the ends of 
the newly divided bacilli press against each other (B, Fig. 1, X), and 
cause the proximal ends to be directed outwards at a considerable angle 
from the original chain (B, Fig. 2, X). As growth progresses a process 
consisting of two parallel bacilli is thus formed (B, Figs. 3, 4, 5, X). 
In deep growths of organisms belonging to this group typical 
slipping post-fission movements follow division, but whether the deep 
colonies ultimately produced are small and more or less rounded or large 
and branched and “ root-like ” seems to depend on the capacity of the 
organisms producing them to overcome the resistance of the agar. 
