370 
Bacteria, tlieir Nature and Function. 
shape, and of a fairly uniform size ; a few only are shorter, and 
arranged in the form of a dumb-bell, indicating that one of the 
longer individuals has by fission split up into two smaller individuals. 
But a glance at a third impression preparation, of which was shown 
a photograph (Proteus), demonstrates that while there are a few 
chains of cylindrical bacilli, indicating successive division of the 
individuals and the new offsprings remaining joined end to end — 
thus constituting what is spoken of as a Leptothrix — there are 
other threads in the colony which either show a division into 
cylindrical elements only imperfectly or not at all, appearing uniform 
and unsegmented threads ; where the segmentation is imperfect the 
individuals are of very various lengths, some not longer than those 
typical bacilli in the first- mentioned chains, others three and more 
times as long. These appearances indicate that the multiplication of 
the bacilli does not always take place in that typical manner in which 
it is generally represented ; viz. one individual elongates a little, 
then splits up into two short individuals ; but a bacillus may go 
on elongating till it reaches the manifold length of the typical rods, 
and, having reached this great length, then segments off into a great 
number of cylindrical rods. This mode of multiplication can be 
made out not only in these impression preparations, but can be 
actually observed in the fresh condition under suitable conditions, 
e.g. on the warm stage of the microscope. 
That this mode of growth appertains not only to cocci and 
bacilli, but also to the third morphological group of bacteria, viz. 
the Vibrios, or Spirilla, is ascertained by the fact that often one 
vibrio, i.e. a more or less curved rod-shaped individual or a comma- 
shaped bacillus, grows into a uniform homogeneous spiral or wavy 
thread, which is capable of splitting up into a number, i.e. a chain 
of comma-shaped vibrios. 
We have then the typical mode of division by which one in- 
dividual, a Coccus, or Bacillus, or Vibrio, as the case may be, slightly 
enlarges, and then by fission divides into two ; or an individual 
continues to grow to abnormal size or length, and then splits up 
into a series of individuals of the typical size ; this latter mode of 
multiplication implies a deficiency of fission for the time being, and 
is not, as far as can be made out, due to any abnormal conditions 
affecting the growth, for in many species this occurs in recent and 
active colonies under conditions which in all other respects must be 
pronounced as favourable for growth and multiplication. 
Another interesting appearance, shown by some species of 
bacteria, is generally ascribed to degeneration or involution, i.e. the 
bacteria assume peculiar abnormal shapes stated to be due to ab- 
normal influences, insufficient or unfavourable soil, unfavourable 
temperature, &c., &c. ; but while it is true that such influences do 
produce abnormal shapes, disintegration, &c., there are certain 
changes in shape that are observed in some species of bacteria while 
growing under perfectly favourable conditions and with the normal 
rapidity, and which are anything but degenerating. 
A recent colony of the Bacillus anthracis, like the photograph 
