38 The Story of the Bacteria 



times only under the microscope, little points 

 or masses scattered through the gelatin, which 

 are colonies of bacteria, each one consisting 

 of hundreds 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 

 more of the original germs either of the same 

 or different species were solidified in the gela- 

 tin when it cooled at the same place, and then 

 the resulting colony will consist of all the 

 organisms which have grown at this point, 

 mixed together or growing closely side by 

 side. In most cases, however, the little colo- 

 nies are composed of the descendants of a 

 single germ, and if we put the gelatin plate 

 under the microscope we can see the different 

 forms of the colonies which have grown from 

 the different species. The differences in the 

 mode of growth of the bacteria when planted 

 and studied in this way are manifold: some 

 are colored, red, green, yellow, orange, violet, 

 brown, etc.; some are colorless, some have 

 sharply defined smooth edges, some are jagged 



