REPRODUCTION AMONG THE LOWER BACTERIA. 5 



Reproduction among the Lower Bacteria. When a 

 bacterial cell is placed in favourable surroundings it multi- 

 plies ; as has been said, this, in the great majority of cases, 

 takes place by simple fission. In the process a constriction 

 appears in the middle and a transverse unstained line 

 develops across the protoplasm at that point. The process 

 goes on till two individuals can be recognised, which may 

 remain for a time attached to one another, or become 

 separate, according to the character of the envelope, as 

 already explained. In most bacteria growth and multiplica- 

 tion go on with great rapidity. A bacterium may reach 

 maturity and divide in from twenty minutes to half an hour. 

 In the latter case a simple calculation will show that, at the 

 end of twenty-four hours, from one individual 17,000,000 

 similar individuals will be produced. As shown by the 

 results of artificial cultivation, others, such as the tubercle 

 bacillus, multiply much more slowly. Sometimes division 

 proceeds so rapidly that the young individuals do not reach 

 the adult size before multiplication again occurs. This 

 may give rise to anomalous appearances. When bacteria 

 are placed in unfavourable conditions as regards food, etc., 

 growth and multiplication take place with difficulty. In 

 the great majority of cases this is evidenced by changes in 

 the appearance of the protoplasm. Instead of its maintain- 

 ing the regularity of shape seen in healthy bacteria, various 

 aberrant appearances are presented. This occurs especially 

 in the rod- shaped varieties, where flask-shaped or dumb-bell- 

 shaped individuals may be seen. The regularity in structure 

 and size is quite lost. The appearance of the protoplasm 

 also is often altered. Instead of, as formerly, staining well, 

 it does not stain readily, and may have a uniformly pale, 

 homogeneous appearance, while in an old culture only a 

 small proportion of the bacteria may stain at all. Some- 

 times, on the other hand, a degenerated bacterium contains 

 intensely stained granules or globules which may be of large 

 size. Such aberrant and degenerate appearances are referred 

 to as involution forms. That these forms really betoken 

 degenerative changes is shown by the fact that, on their 



