50 
Growth of Bacilli 
in the right hand peripheral part of the colony is due to active move¬ 
ment during the exposure of the plate and a smaller blurred portion 
on the other side is due to the same cause. On further incubation the 
colony only increased slightly in size, but continued multiplication of 
the bacilli led to the formation of several layers. 
Plate VIII, Fig. 7 illustrates a fully formed colony of this type with 
a thicker centre and thinner margins. 
After general surface expansion has been arrested by the drying of 
the surface of the medium and raised areas of growth of considerable 
size have been produced further incubation may lead to an attempt at 
extension in the form of thin twisted, often branched ramifications. 
Fig. 5 shows on the right a number of sucb surface ramifications 
and on the left some thinner twisted threads due to extension in the 
depth. The two dark masses in the upper right and left corners are 
rounded masses at the extreme ends of long lateral processes. Fig. 6 
shows the rare condition of a small round colony developing branching 
ramifications. 
On somewhat dry agar a great tendency towards the formation of 
long partially segmented threads, which are probably important factors 
in the production of colonies with spreading processes, has been 
frequently noticed. The ramifications just described are also developed 
from radiating threads which grow rapidly outwards from the colony. 
Later segmentation and multiplication occur in the threads and 
consequently thin processes consisting of parallel bacilli are formed 
along the lines of the original threads. 
Another closely allied species, which exhibits a considerable tendency 
to form long partially segmented threads, behaves somewhat differently. 
On thin agar the colony after a few hours’ growth usually consists of a 
bundle of parallel threads (Diagram 14, Figs. 1, 1 a) produced by typical 
slipping movements, as illustrated in Diagram 12, series A. After 
further growth the bundle has a wavy or sometimes looped appearance, 
and threads may usually be seen projecting from it in various directions 
(Diagram 14, Fig. 2). On dry agar further incubation only results in 
some increase in length and in waviness of the central bundle. On 
moist agar the central parallel bundle often becomes markedly 
looped and twisted, and the projecting threads also produce twisted 
and often looped processes (Diagram 14, Fig. 3). Even though many 
loops may be produced on the process (Fig. 4) the latter cannot be 
mistaken for the process of a true loop-forming organism, for in all 
cases careful observation shows distinct evidence of “ slipping,” and 
