CULTURES IN LIQUID MEDIA. 63 
For larger quantities of liquid than can be held in an ordinary 
test tube the small flasks with a flat bottom, known as Erlenmeyer 
flasks, are very convenient (Fig. 33). 
In his earlier researches Pasteur used flasks and tubes of various 
forms, which served a useful purpose, but have been displaced in his 
laboratory by the simpler form of apparatus shown in Fig. 34. 
This is a little flask having a cover which is ground to fit the neck. 
This cover is drawn out above into a narrow tube which admits 
oxygen to the flask through a cotton air filter. To obtain access 
to the interior of the flask for the purpose of introducing bacteria 
to start a culture, or to obtain material for microscopical examina- 
tion, the cover is detached at the ground joint by a gentle twisting 
motion. 
There is much less danger that a sterile culture liquid will become 
Fia, 33. Fig. 34. 
contaminated during the momentary removal of the cover from 
one of these little flasks, or of the cotton plug from a test tube, than 
is usually supposed. Abundant laboratory experience demonstrates 
that such contamination by bacteria floating in the atmosphere rarely 
occurs. The spores of mould fungi are commonly more abundant 
in the air, but even these do not very frequently fall into the culture 
liquid when the tube is opened to inoculate it with the bacteria it is 
proposed to cultivate. This inoculation is best made with a platinum 
wire, bent into a loop at the free extremity, and sealed fast into the 
end of a glass rod (Fig. 35), This is sterilized in the flame of a 
Bunsen burner or alcohol lamp by bringing the platinum wire to a 
red heat and passing the end of the glass rod which carries it 
through the flame several times. With this instrument we may 
transfer a little drop from aculture to the sterile fluid in another 
