DUST AND ITS DANGERS 337 



housekeeper and the janitor, it is now known that the chief 

 danger to man lies in coming in contact with live dust. We 

 shall see in Chap. VIII that many communicable diseases such 

 as tuberculosis, pneumonia, colds, grippe, diphtheria, and 

 others are caused by living microorganisms. These and other 

 similar organisms constitute live dust. Most, if not all, of these 

 disease germs die quickly when exposed to direct sunlight or 

 high temperature. Therefore, the dust blown in from the 

 street, or the fine ashes coming from the stove or furnace, can 

 not be looked upon as particularly dangerous, no matter how 

 annoying such dust may be. 



371. House Dust. House dust is almost certain to consist 

 of both live dust, living organisms, and dead dust. It is of 

 great importance, therefore, that so far as possible all dust be 

 removed from rooms where people live or congregate, not sim- 

 ply because it looks bad, but principally because it endangers 

 the health of the occupants. Ordinary sweeping with a broom 

 or carpet sweeper does not remove the most dangerous por- 

 tions of the dust. Dusting the room with a dry dusting cloth 

 does not remove much of the dust. Such methods remove 

 only the large particles of dirt which are not particularly 

 dangerous, merely unsightly, and remove the finer dust from 

 the more exposed surfaces allowing it to settle again in the 

 unobserved places. No system of house cleaning and dusting 

 is effective or much worth while, so far as health of the 

 occupants is concerned, unless it really removes the dust from 

 the house. 



Exercise 74. Observing Dus in the Air of a Room 



Darken a room by drawing the window shades (either a living 

 room at home or the schoolroom will do) leaving a small crack at 

 one window through which the direct sunlight may enter. Observe 

 the dust particles floating in the air. Why is it that they now be- 

 come visible? With a broom sweep the floor or carpet near the 

 window. Does the amount of dust floating in the air increase? 

 With a dry dusting cloth wipe the walls or furniture and shake the 

 cloth in the ray of sunlight. Note the result. 

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