70 LABORATORY GUIDE IN BACTERIOLOGY 



SECTION 2 



COLLECTING AND CULTIVATING MICRO-ORGANISMS 

 FROM THE AIR 



EXERCISE I 



1. Sterilize all petri dishes in the hot-air sterilizer for 

 one hour at i6o° C. 



2. Melt two tubes of plain agar, one of dextrose 

 agar, and two of beerwort agar, in a water bath. The 

 water bath (Fig. 25) is a round copper vessel with a 

 number of holes in the top. These holes a^e large 

 enough to allow a culture tube to slip in. A thermom- 

 eter is passed through a rubber cork with a hole in its 

 center, and inserted into one of the holes in the water 

 bath. Water is then poured into the apparatus until 

 the level is slightly higher than the media in the tubes 



and the thermometer 

 lowered until the mer- 

 cury bulb is immersed 

 in the water. The cul- 

 ture tubes are then 

 slipped in, and the 

 water heated to 100° C. 

 3. Singe the cotton 

 stopper of the liquefied 

 agar tubes in the flame, 

 remove the cotton 

 stopper, pass the mouth 

 ajid about one inch of 

 the tube through the 

 flame, and pour the 



