162 ELEMENTARY BIOLOGY 



use in school buildings and other public places is forbidden. 

 From the point of view of cleanliness, as well as from the 

 point of view of health, wet sweeping with damp or oiled 

 sawdust or pieces of wet newspaper and the wiping off of 

 dust with a damp or oiled cloth are more satisfactory than 

 the old-fashioned methods of dry sweeping and dusting. 



FIG. 55. Dusting for looks and dusting for health 



The feather duster throws the dust into the air, where it cannot be seen, but where it 



can do more harm than on top of the bookcase or picture-frame. The damp or oiled 



cloth removes the dust not only from the furniture but from the way of doing harm 



192. Smoke. A very common source of air contamination, 

 especially in manufacturing cities, is the smoke from furnaces 

 of all kinds and from railway locomotives. Experiments have 

 shown that the smoke interferes with the growth of plants, 

 and it is certain that smoke affects the health of human 

 beings. Progressive cities now prohibit the pollution of air 

 by smoke. 



193. Tobacco smoke. Whether we mind it or not, tobacco 

 smoke spoils the air for us and is a real injury. Apart from 

 possible injury to the smoker, those who do not smoke deserve 



