230 BACTERIOLOGY. 



the tip of a sterile platinum needle, and thus transfer 

 them to a cover-glass for microscopical examination, or 

 to new media where they may develop in pure cultures 

 and show their growth characteristics. 



The Study of Plate Cultures in Gelatin Media. 



The gelatin media have one marked characteristic to 

 be noted which never occurs upon agar namely, some 

 of the colonies will be lying in or surrounded by slightly 

 opaque fluid, due to the liquefaction of the gelatin. 

 (See paler and larger colonies in Fig. 28.) In using 

 nutrient gelatin one must always remember not to allow 

 it to stay where the temperature is over 20 C., for if 

 that happens the media will melt, nor must the lique- 

 fying colonies be allowed to grow for too long a time, 

 or the entire media will become fluid. 



FIG. 81. 



Stab cultures of three cholera spirilla in gelatin, showing in upper portion 

 of growth considerable liquefaction of nutrient gelatin. 



Pure Cultures. If we transfer without contamination 

 bacteria from a colony formed from a single organism 



