36 THE STORY OF THE BACTERIA. 



We mix thoroughly a small amount of the 

 bacteria-containing water with a much larger 

 amount of the above-described nutrient gela- 

 tin, rendered just fluid by heat. Then we 

 pour this mixture out onto a glass plate which 

 has been carefully sterilized by heat, so as to 

 form a thin layer, which soon cools and be- 

 comes solid. The glass plate is now covered 

 with a bell-jar to prevent the access to it of any 

 bacteria which may be floating in the air, and 

 to prevent its drying, and set it away at the 

 proper temperature. The individual bacteria 

 which were scattered through the gelatin layer 

 will presently commence to grow. 



After a few hours or days, as the case may 

 be, if we look at the gelatin-film we see, some- 

 times with the naked eye, sometimes only un- 

 der the microscope, little points or masses 

 scattered through the gelatin, which are colo- 

 nies of bacteria, each one consisting of hun- 

 dreds or thousands of the organisms which 

 have grown from the single organism which 

 was fixed at that point as by a solid wall when 

 the gelatin cooled. 



Of course, it sometimes happens that two or 



