98 
HOUSEHOLD BACTERIOLOGY 
Dust Gardens 
Settling 
of Bacteria 
and Molds 
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 
