. A manual of bacteriology. Bacteriology. CULTURE-MEDIA. 77 ,S<S#tK?^^ 2=^ The necessity for sterilization of the tubes before filling them with the medium has been questioned, and it is probably un- necessary as far as the preservation of the culture-medium is concerned, but it will be found that the cotton plugs fit much better after sterilization with dry heat. During this and subse- quent sterilizations the tubes are held in a wire basket. Filling of the Tubes.—A special funnel closed with a stop- cock for filling tubes with liquefied media is often recom- mended. They may readily be fi
. A manual of bacteriology. Bacteriology. CULTURE-MEDIA. 77 ,S<S#tK?^^ 2=^ The necessity for sterilization of the tubes before filling them with the medium has been questioned, and it is probably un- necessary as far as the preservation of the culture-medium is concerned, but it will be found that the cotton plugs fit much better after sterilization with dry heat. During this and subse- quent sterilizations the tubes are held in a wire basket. Filling of the Tubes.—A special funnel closed with a stop- cock for filling tubes with liquefied media is often recom- mended. They may readily be filled with an ordinary funnel of small size. During the filling, the neck of the test-tube where it comes in contact with the cotton must not be wet with the medium. Or- dinarily about 7 to lo are placed in a test-tube. For Esmarch's roll-tubes a somewhat smaller quantity is desirable. The sterilization of tubes containing culture-media is always done by steam and has been sufficiently described. It, is to be remembered that the solidifying power of gelatin is impaired by too pro- longed heating, while heating is less likely to damage other culture-media. The media which are sterilized at a low temperature (70° C). should be tested for two days in the incubator to determine whether sterilization has been effective. It is the universal experience in bacteriological laboratories that occasionally culture-media will become contaminated with extremely resist- ant spores which fail to be sterilized by the ordinary pro- cesses, an occurrence which causes great annoyance and calls for the exercise of much patience. Sometimes, also, moulds attach themselves to the plugs, especially if they are moist, and send their filaments down through the cotton; finally, having reached the lower edge of the cotton, their spores may fall upon the medium, grow there and ruin Fig. 18.—Wire basket for Please note that these images are extracted from scanned page images that m
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