CHAPTER VI 



COLLECTING BACTERIA FROM THE AIR 



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

 one hour at i6o° 



2. Melt two tubes of plain agar and one of glucose- 

 agar in the water-bath. The water-bath (Fig. 20) is a 

 round copper vessel with a number of holes in the top. 



These holes are large enough to allow a culture-tube to 

 slip in easily. A thermometer is passed through a rubber 

 cork with a hole in its center, and inserted into one 

 of the holes in the water-bath. Enough water is then 

 poured into the apparatus to fill it about two-thirds, and 

 the thermometer is lowered until the mercury bulb is 



37 



