GENERAL BACTERIOLOGY 



EXERCISE 2. PLUGGING FLASKS AND TUBES. 



GENERAL DIRECTIONS. When the flasks, test-tubes and fer- 

 mentation tubes are thoroughly dry they are to be plugged with 

 cotton. The cotton for this purpose should be non-absorbent and 

 of the best quality, i. e., as free from foreign matter as possible. 

 The plugs should be sufficiently loose to permit the interchange of 

 gases and at the same time tight enough to support the weight of 

 the vessel and its contents, otherwise they are apt to be pulled out 

 in handling the vessels. The cotton should be rolled into a cylin- 

 der of the proper diameter and long enough to extend into the 

 mouth about 2y 2 cm. (1 in.) and project sufficiently to protect the 

 lips from dust. The plug should be pushed in straight and not 

 twisted; the surface next to the glass must be perfectly smooth, 

 presenting no creases for the entrance of dust. 



REFERENCES. A. 127; H. 44; M. & R. 49; McF. 164; P. 223. 



SPECIAL DIRECTIONS. Plug all test-tubes, flasks and fermenta- 

 tion tubes in your possession. 



EXERCISE 3. STERILIZATION OF GLASSWARE. 



GENERAL DIRECTIONS. The glassware thus prepared is ready 

 for sterilization, which process is accomplished in an apparatus 

 called the hot air sterilizer. This is a sheet iron or copper box with 



a double wall which permits of rapid 

 heating. The apparatus should be so ar- 

 ranged that a temperature of 150 C. can 

 be quickly reached and readily main- 

 tained. In such a sterilizer all glassware 

 L to be used for the reception of culture 

 media, such as flasks, test-tubes, Petri 

 dishes, etc., is submitted to a temperature 

 of 140-150 C. for 1 hour, or until the 

 cotton plugs are slightly browned; this 

 change being due to the incipient char- 

 ring of the cotton. The test-tubes are 

 placed erect in square baskets made of 

 galvanized iron wire. When the air in 

 the sterilizer has cooled to about 40 C. 

 the glassware can be taken out and stored ready for use. The Petri 

 dishes are not to be opened until used for culture purposes. 



REFERENCES. A. 75 and 127 ; H. 36 ; M. & R. 29 ; McF. 164 ; 

 P. 223. 



; x 



Fig. 1. Hot Air Sterilizer, 

 (Muir & Ritchie). 



