MULTIPLICATION OF BACTERIA. 27 







great power of resisting adverse conditions. They may be 

 dried for months or even years without losing their power 

 of growth. They may be heated to a temperature even 

 above that of boiling water without injury, for, if they are 

 later brought into proper conditions for growth, the spores 

 germinate and develop new organisms like the original that 

 produced them. They are evidently developed for the pur- 

 pose of enabling the species to resist the adverse conditions 

 of drying, to which it must occasionally be subjected, and 

 to preserve it under conditions which would otherwise de- 

 stroy the bacteria. Not all bacteria form spores, and the 

 question whether a species which we are studying forms 

 spores or not is one of great practical significance in teach- 

 ing us how to handle it, since, while the spores can with- 

 stand heat and drying, the active growing bacteria are 

 commonly killed by a moderate heat. These facts are of 

 especial importance in all matters connected with disinfec- 

 tion. 



Rapidity. One of the most important factors connected 

 with the life of bacteria, and the chief fact upon .which 

 their significance in nature is dependent, is their exception- 

 ally rapid power of multiplication. The elongation of a 

 rod and its division into two, followed by a repetition of the 

 process, may be extremely rapid. Frequently it takes not 

 more than half an hour for the whole phenomenon to 

 occur, and sometimes even less time is required. Such divi- 

 sion in geometrical ratio results in an increase in numbers 

 which is almost inconceivably rapid. If this rate of multi- 

 plication could be maintained for twenty-four hours there 

 would be produced, as the offspring of a single bacterium, 

 some seventeen million descendants, and in five .days a mass 

 sufficient to fill the oceans. This rate of multiplication is, 

 of course, not continued for any great length of time, for 

 various checking influences are at work to stop the growth. 

 But this possibility of reproduction represents an almost 



