68 



PURE AIR 



illustration) . These little masses of material have not grown 

 from nothing. They increase in size day by day. They must 

 be alive. Since everything in the dish was dead, we have 

 to conclude that they came from the air. If we were to 

 examine the material under a very high-power microscope, 

 we would find it composed of millions upon millions of tiny 

 plant forms known as bacteria or m"olds. These tiny plants 



DfcY BROOM 



DAMP BROOM 



CARPET SWEEPER, 



VACUUM CLEAN CK> 



Which of the above methods is the best ? What evidence is shown ? 



grow and thrive in our homes under conditions which we 

 shall investigate more thoroughly later. 



Proper methods of sweeping and dusting. If these 

 germs are present in dust, then it is important for us to 

 have methods of sweeping and dusting which will not raise 

 dust. A good home project for girls and boys would 

 be the working out of the best methods for cleaning their 

 own homes. If we are fortunate enough to have electricity, 

 then an electric vacuum cleaner which sucks up the dust 



