BACTERIOLOGICAL TECHNIQUE. 221 
ent media are stored in large quantities in round or flat- 
bottomed Erlenmeyer flasks (Fig. 23). From these, as 
needed, glass tubes (Fig. 24) are filled. Glass dishes 
with covers (Petri dishes, Fig. 27) and flat flasks are 
used for growing bacteria in or upon thin layers of 
media. When small amounts of media are taken fre- 
quently from flasks, Pasteur’s flasks (Fig. 25) are of 
Glass test-tubes. 
great convenience. They consist of a flask with a 
ground-glass neck, over which fits a cap. This cap 
may or may not terminate, as desired, in a narrow 
tube, which is plugged with cotton. The cap keeps 
the edges of the flask free from bacteria and prevents 
the cotton from sticking. 
