138 



BACTERIA, YEASTS, AND MOLDS 



particularly milk. So ubiquitous are they that it is an abso- 

 lute impossibility for the housewife, by any means at her 

 command, to keep her pantry and food free from them. 



These facts forcibly emphasize the futility of the common 

 method of sweeping and dusting rooms. Bacteria are heavier 

 than the air and, if undisturbed, settle and lie quietly upon 

 floors, tables, etc. Every sweeping the room receives stirs 

 them up. A dustbrush sends them flying through the room, 

 only to settle down again later. On the other hand, wiping 



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

 after a class has occupied a schoolroom. 



with damp cloths removes the bacteria and this is a proper 

 meth(5d of cleaning. This is especially true for kitchens and 

 pantries where food is exposed to the air, and for school- 

 rooms where there is likely to be a collection of numerous 

 kinds of bacteria, including some disease germs brought by 

 the many children. Fig. 59 shows two plates, one exposed 

 to the air before and the other after a school session. The 

 relative abundance of bacteria floating in the air is clearly 

 shown. These facts forcibly show the advantage of vacuum 

 cleaners, which remove the dirt without stirring up the dust. 



