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, whirh, 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 sarcinse, for 

 example, which divide more or less regularly in three 

 directions. Instead of becoming separated from each 



