I20 BACTERIA, YEASTS, AND MOLDS 



particularly milk. So ubiquitous are they that it is an 

 absolute impossibility for the housewife, by any means 

 at her command, to keep her pantry and food free fronr 

 them. 



These facts forcibly emphasize the futility of the com 

 mon method of sweeping and dusting rooms. Bacteric 

 are heavier than the air and if undisturbed settle and lie 

 quietly upon floors, tables, etc. Every sweeping the rooff 

 receives stirs them up. A dustbrush sends them flying 



Fig. 59. Petri dishes exposed, one, a, before, and the other, b, 

 after a class has occupied a schoolroom. 



through the room only to settle down again later. On the 

 other hand, wiping with damp cloths removes the bacterid 

 and is the only proper method of cleaning. This is espe 

 cially true for kitchens and pantries where food is exposec 

 to the air, and for schoolrooms where there is likely to bt 

 a collection of numerous kinds of bacteria, including some 

 disease germs brought by the many children. Fig. 5c 

 shows two plates, one exposed to the air before and the 

 other after a school session. The relative abundance ol 

 bacteria floating in the air is clearly shown. 



