34 AGRICULTURAL BACTERIOLOGY. 



side by side. It is only under some veiy exceptional condi- 

 tions that large numbers of a single species are found together, 

 wholly unmixed with other species. Such a condition, where 

 great quantities of a single species of bacterium are associated, 

 uncontaminated with any individuals of another species, is 

 called by the bacteriologist a pure culture. While such pure 

 cultures are very unusual or almost never found in nature, 

 they are easily enough produced in the bacteriologist's labora- 

 tory by artificial methods. Pure cultures have been coming 

 into prominence in recent years, and are to-day prepared by 

 bacteriologists for various purposes. They always represent 

 artificial preparations and, therefore, are usually unlike any 

 natural conditions of bacterial life. 



BACTERIA, AS IMPORTANT AGENTS IN PRODUCING CHEMICAL 



CHANGE. 



When we consider the extremely minute size of bacteria, it 

 seems strange, at first, that they can be important agents in 

 nature. No one of them, to be sure, can accomplish very 

 much, but when we remember their power of multiplica- 

 tion we can readily understand how it is that they become of 

 great importance. Of course, the figures given above, showing 

 a possibility of 17,000,000 offspring in twenty -four hours, are 

 extreme and, probably, are never realized in nature. Most 

 bacteria do not multiply as fast as this even under the most 

 favorable conditions ; but in all cases they multiply with an 

 almost inconceivable rapidity, and this great power of multi- 

 plication makes them forces of great significance. They are 

 like the snowflakes, each insignificant in itself, but when com- 

 bined, forming the irresistible avalanche. While they are 

 growing and multiplying with such vigor, they are sure to 

 produce profound chemical changes in the food upon which 

 they feed. It is to these chemical changes that their impor- 

 tance in agriculture is due. 



. 



