HOUSEHOLD BACTERIOLOGY 



Settling 

 of Bacteria 

 and If olds 



sweeping a carpeted room and another when the same 

 room, with closed windows, has been left undisturbed 

 for two or three hours, there is a marked difference 

 in the number and kind of colonies which will grow. 



Figures 46 to 49 inclusive are photographs of "dust- 

 gardens" planted in various places by different persons 

 under varying conditions. The plate shown in Fig. 

 46 was planted after a carpet had been swept with a 

 dampened broom. The plate was left open ten 

 minutes. 



The damp broom caught and held much of the dust 

 which would have been thrown into the air if a dry 

 broom had been used. If the sweeping had been done 

 carelessly without thought of the dust, many more 

 plants would have found their way to the garden plot. 

 As it was, the number of spots shows how carefully 

 sweeping ought to be done in order that the air may 

 not be charged with dust which is thereby simply 

 changed in place, not removed from the room. It 

 soon returns to the floor or carpet. 



Plate Fig. 47 was exposed for ten minutes in the 

 same place after the room had been quiet for three 

 hours and the dust had therefore settled considerably. 

 The fewer spots show that the air had become much 

 freer from dust than when Fig. 46 was planted. 



The greater number of molds present in this plate 

 shows that the bacteria, being heavier, settle first. The 

 presence of so many molds shows that even after 

 three hours' quiet, the air may still be sufficiently 



