20 ESSENTIALS OF BACTERIOLOGY 



and dividing the cell into two equal parts, just as occurs in the 

 higher plant and animal cells. (See Fig. 4.) 



Successive divisions take place, the new members either exist- 

 ing as separate cells or forming part of a community or group. 

 It has been computed that if division takes place every hour, 

 as it often does, one individual in twenty-four hours will have 

 17,000,000 descendants. 



Spore Formations. Two forms of sporulation, endosporous 

 and arthrosporous. 



Endosporous. First, a small granule develops in the pro- 

 toplasm of a bacterium; this increases in size, or several little 



Fig. 4. Division of bacteria: a, Division of a micrococcus; b, division of 

 a bacillus (after Mace). 



granules coalesce to form an elongated, highly refractive, 

 clearly denned object, rapidly attaining its real size, and this 

 is the spore. The remainder of the cell-contents has now 

 disappeared, leaving the spore in a dark, very resistant mem- 

 brane or capsule, and beyond this the weak cell-wall. The 

 cell-wall dissolves gradually or stretches and allows the spore 

 to be set free. 



Each bacterium gives rise to but one spore. It may be at 

 either end or in the middle (Fig. 5) . Some rods take on a pecu- 

 liar shape at the site of the spore, making the rod look like a 

 drum-stick or spindle clostridium (Fig. 6). 



Spore Contents. What the real contents of spores are is not 



