VACUUM CLEANERS 



121 



air, sometimes living on dust particles and sometimes un- 

 attached to anything. Only a few of the bacteria are harm- 

 ful, and they are usually not very abundant. Sunlight 

 kills most of them in a short time, but moisture and dark- 

 ness furnish conditions favorable for them. They are 



Courtesy of Elgin Sales Corporation 

 A MODERN STREET SWEEPER 



The left end is the forward end. This machine sprinkles, sweeps, and 

 collects the sweepings. The operator is working the lever which 

 empties the machine. 



particularly abundant in the dust of the street and wherever 

 foul refuse accumulates. When they get into a house they 

 settle and multiply rapidly if they happen to light upon a 

 warm, moist place where the sunshine is not too bright. 

 Ordinary dusting and sweeping simply scatter them about 

 and keep them floating 'in the air for hours, for us to 



