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GENERAL BIOLOGY OF MICRO-ORGANISMS 



that there are doubtless many kinds of bacteria that do not find 

 favorable conditions for development on ordinary culture- 

 media. The reaction of the medium has an important influence 

 upon the 'development of these water bacteria in plate cultures. 



FIG. 83. Jeffer's plate (Bausch and Lomb}. For counting colonies of bacteria on 

 circular plates. The area of each division is one square centimeter. 



When the number of colonies is small, there is no difficulty 

 in counting them as they appear in the ordinary Petri dish. 

 When the number is large, some kind of mechanical device may 



