BACTERIA 



343 



forms and as a result of their activity various substances are 

 produced, the accumulation of which check their activity. 

 Some forms, called anaerobic, get along better without air, while 

 others, called aerobic, must have air. 



Their reproduction is accomplished by cell division, which is 

 not so complex and takes place more rapidly than in the cells of 



\N\\ 



9mm 





Fig. 296. — Bacillus subtilis, a Bacterium of decay. Above, the active 

 form (X 1500); at tlje left, below, spore stage (X 800); at the right, below, 

 the zoogloea stage (X 500). 



the higher plants. Cell division is so rapid that the progeny of 

 one individual often runs into many millions in twenty-four 

 hours. The new individuals may separate immediately after 

 division is complete or cling together in filaments. Sometimes 

 in shrinking the protoplasm and enclosing it in an inner heavy 

 wall in preparation for the resting stage, the protoplasm divides 

 and each separate mass of protoplasm forms a spore. Since each 

 spore is an individual in a dormant protected state, the formation 

 of more than one spore results in the multiplication of individuals. 



