THE NATURE OF BACTERIA. 3! 



seems to be to enable the bacterium to exist through condi- 

 tions of adversity. They have very 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 with- 

 out injury, for, if they are later brought into proper conditions 

 for growth, the spores germinate ancj develop new organisms 

 like the original that produced them. They are evidently de- 

 veloped for the purpose 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 destroy 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 

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

 stand heat and drying, the active growing bacteria are com- 

 monly killed by a moderate heat. These facts are of especial 

 importance in all matters connected with disinfection. 



Rapidity. One of the most important factors connected 

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

 significance in agriculture is dependent, is their exceptionally 

 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 take place, and sometimes 

 evert less time is required. Such division in geometrical ratio 

 results in an increase in numbers which is almost inconceivably 

 rapid. If this rate of multiplication 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 



