14 THE GENERAL CHARACTERS OF MICROORGANISMS. 



much smaller number of species. It is frequently uncertain whether 

 a species described by one bacteriologist is the same as that de- 

 scribed by another under the same name. The difficulties in the 

 way of a proper description and classification of the species of 

 bacteria have hitherto been insurmountable, and at the present 

 time the subject is in such extreme confusion that no one except an 

 expert can understand it. Fortunately this confusion of species 

 is of no importance for our purpose. Agricultural bacteriology is 

 not at present concerned with the problem of the species. All that 

 it is necessary for us to know in connection with our subject will be 

 referred to in the separate sections in the following pages, and the 

 subject of the classification of bacteria may be left without further 

 consideration. 



Multiplication of Bacteria. As already mentioned, the 

 primary method of the multiplication of bacteria is by simple 

 division. Bacteria are so minute that it seems strange to assign 

 to them much of a part to play in nature's processes. But their 

 extraordinary power of multiplication gives them unlimited possi- 

 bilities. 



The elongation of a rod and its division into two parts, followed 

 by a repetition of the process, may be extremely rapid. Frequently 

 it does not take more than half an hour for the whole phenomenon 

 to take place, and sometimes even less time is required. Such 

 division, in geometrical ratio, results in an increase in numbers 

 that is almost inconceivably great. If a division once an hour 

 could be maintained for twenty-four hours, there would be pro- 

 duced, as the offspring of a single bacterium, some seventeen million 

 descendants, and in five days there would be a mass sufficient to fill 

 the oceans. This rate is, manifestly, not continued for any great 

 length of time, or the world would be full of them; their growth is 

 checked by lack of food, and still more by the substances they se- 

 crete, which act as poisons. But this possibility of reproduction 

 represents an almost unlimited power, constantly curbed by the 

 lack of proper conditions. Bacteria may thus be looked upon as 

 possessing a wonderful possibility of reproduction, a force of in- 

 conceivable magnitude, held more or less in check by adverse condi- 



