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. 
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 
