I08 BACTERIA, YEASTS AND MOLDS 



reproduce themselves once every half hour, the result of 

 which is that a single bacterium will have become two in 

 a half hour, four in an hour, eight in an hour and a half, 

 and so on. This increase of progeny by geometrical pro- 

 gression results in the production of descendants with 

 immense rapidity. If the rate of multiplying above men- 

 tioned should continue for twelve hours, the result would 

 be the production of about seventeen million offspring. 

 Such a rapid production as this does not continue very 

 long, through lack of food and other adverse conditions. 

 If it did, the world would soon become filled with bacteria, 

 crowding everything else out of existence. 



Recognizing that they have this wonderful power of 

 multiplication, we can readily see that bacteria represent 

 a force in nature of almost inconceivable magnitude. 

 This rate of growth is a possibility for a while at least, 

 and in order that such a multiplication should continue 

 it is only necessary that the bacteria should be given 

 proper food and proper conditions. The results are mar- 

 velous. Although they are so small that a single one 

 can accomplish practically nothing in nature, the fact that 

 this single one can in twenty-four hours produce millions 

 of descendants gives to bacteria almost unlimited power. 

 An appreciation of this fact is fundamental to an under- 

 standing of the action of bacteria. Since one in the 

 course of a few hours may become hundreds of thousands, 

 and a little later its progeny may be millions, it is clear 

 that in order to protect any material from the action of 

 bacteria something more is necessary than simply to 

 reduce the number of microorganisms. If the material 

 is to be protected from them, every single bacterium must 



