20 Bacteria in Relation to Country Life 



favorable conditions it may be extended over a much 

 longer period, determined by the food-supply and the 

 character of the organisms. With division occurring 

 every half-hour, a single individual could become, in 

 one day, the ancestor of 280,000,000,000,000 bacteria. 

 Under actual conditions, multiplication never proceeds 

 at such a rapid,' uniform rate, for many of the cells 

 die, and the food in the medium is exhausted. 



Conditions that retard bacterial growth. — The multi- 

 plication of the organisms involves, not only a reduction 

 in the food-supply, but, also, an accumulation of sub- 

 stances injurious to the bacteria. These injurious sub- 

 stances may be formed within the bodies of the bacteria • 

 and excreted into the surrounding medium, or they 

 may develop outside of the bacterial bodies. In either 

 case, the growth of the bacteria is retarded more and 

 more as the quantity of these injurious materials is 

 increased and finally comes to a standstill, even though 

 all the food in the medium is not yet entirely consumed. 



We find an analogy in the injurious effect on plants 

 and animals of their own excretions, as, for instance, 

 in the case of the uncomfortable feeling caused by the 

 crowding of many people into a small room. Under 

 such circumstances, the gaseous exhalations from the 

 lungs and skin may become sufficiently great in amount 

 to produce distress, and, in extreme cases, severe injury 

 and death. A similar accumulation of excreta in their 

 immediate environment reacts unfavorably on bacteria. 

 Their life-processes become more sluggish, and not only 

 is growth retarded, or entirely stopped, but many of 

 the organisms perish and disintegrate. 



