7° 



MANUAL OF BACTERIOLOGY. 



and 5 inches in length. The tubes should be of a heavier 

 glass than in those used for ordinary chemical work. The 

 New York Board of Health, and some others, use a tube 

 three inches in length without a flange for the cultivation 

 of the diphtheria bacillus on LofHer's blood-serum mixture. 

 Test-tubes should be thoroughly cleaned with a swab before 

 using; they should be boiled with washing-soda, rinsed, filled 

 with hydrochloric acid solution, rinsed and inverted to drain 

 away the fluid. 



Plugs of raw cotton or cotton batting are employed as stop- 

 pers. Some prefer absorbent cotton, but it is likely to become 

 soggy after exposure to steam. The plug 

 should fit smoothly; creases and cracks 

 around the edges are to be avoided. The 

 plug should be tight enough to sustain the 

 weight of the tube when held by the plug. 

 These plugs prevent bacteria from enter- 

 ing or leaving the tubes. 



Sterilization of Test-tubes. — The 

 tubes are to be sterihzed in a hot-air 

 sterilizer for one hour, at a temperature 

 of 150° C. They may be left in until 

 the cotton acquires a light-brown color, 

 but it should not be burned. If the plugs touch the sides of 

 the sterilizer or He against the bottom they may be scorched. 



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 steriUzation 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 filhng tubes with liquefied media is often recommended. 

 They may readily be filled with an ordinary funnel of smaU size. 



Fig. 18. — WiEE Basket 

 FOR Test-tubes. 



