GENERAL CHARACTERISTICS OF BACTERIA. 45 
cell will be seen to elongate, in the case of spherical 
bacteria only slightly, and in the rod-shaped organ- 
isms considerably in one direction. Over the centre 
of the long axis thus formed will appear a slight in- 
dentation in the outer envelope of the cell ; this inden- 
tation increases in extent until there exists eventually 
two individuals. As a rule, the cells separate from 
one another soon after division, but occasionally they 
remain together for a time, forming pairs and chains. 
Under certain conditions of nutrition long threads or 
filaments are formed, which, however, when put in 
contact with new food, break up into fragments. At 
times, when the culture media are exhausted or nearly 
so, the bacilli and spirilla will be found to go on divid- 
ing, with little or no increase in length, and thus coc- 
cus-like forms result ; but when these are given fresh 
food under suitable conditions they elongate and repro- 
duce the usual shaped organisms. According to recent 
investigations on the subject of cell reproduction, the 
division of the cell starts from the protoplasmic layer, 
the central space being passively destroyed, and the 
outer envelop is only secondarily concerned in the 
process. This would indicate that the central space 
is not a true nucleus, otherwise the division of the 
nucleus should precede the cell division. The com- 
plete process of cell reproduction in most varieties 
occupies, under favorable conditions, about twenty to 
thirty minutes. 
But although elongation in the greater diameter 
and transverse division is the rule for the majority of 
bacteria, there are certain groups, as the sarcine, for 
example, which divide more or less regularly in three 
directions. Instead of becoming separated from each 
