BACTERIA, 153 



shapes represent all that have been discovered and 

 studied up to the present time. The single bacte- 

 rium consists of a single cell; and this single cell, 

 simple as it is, carries on all the processes of life. 



As with most one-celled plants and animals, bac- 

 teria multiply by division. The process is a simple 

 one. The single cell divides into two parts, giving 

 rise to two individuals instead of one. These two 

 grow for a short time; then each one divides into 

 two equal parts and four individuals are the result. 

 These four in the same manner give rise to eight, 

 and these eight to sixteen, and so on, the number 

 always doubling. Some kinds divide at short 

 intervals not more than half an hour apart but 

 other kinds require a longer time. 



Dividing once each half hour, one bacterium 

 could thus give rise to several million individuals 

 during a day of twenty-four hours, as can easily be 

 computed. At this rapid rate of multiplication, 

 they would soon fill the world if a sufficient food 

 supply were at hand. The fact is that they soon 

 exhaust their food supply in any one place and die 

 of starvation, or are poisoned by the effect of too 

 many living in one small colony. 



Bacteria require moisture for their propagation 

 and growth. They are distributed everywhere, but 

 active life and growth are manifest only with the 

 presence of moisture. Bacteria, as spores, are in 

 and on all dry substances. Life in the spore state 

 is dormant, just as life in some higher plants is 



