THE STORY OF THE BACTERIA. 37 



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 

 or fringed, some are beaded, or send out little 

 spines ; some cause the gelatin in their imme- 

 diate vicinity to liquefy, so that they come to 

 lie in a little pool of fluid in a pit or depression 

 in the solid gelatin. 



Now, by examining the plate microscopically 

 we cannot only see how many different forms 

 of colonies there are and each different form 



