DUST IN OUR HOUSES. 3 



caused shipwrecks, and dust has caused, and still causes, 

 death. 



More than this, without dust we should probably have 

 no fogs, no clouds, and no rain, there would be no light, 

 no colour in the ocean ; and finally, without dust, the sun's 

 rays would be invisible to us. 



What then is this dust, and where does it come from ? 



Inside our houses it consists chiefly of the minute 

 particles rubbed off carpets, furniture, and the like, by the 

 ordinary wear and tear of daily life. Carpets and clothes 

 are constantly being worn threadbare by perpetual rubbing ; 

 and every time we cut the leaves of a book, wind wool, 

 use a sewing-machine, scratch the legs of table or chair, 

 every time, in fact, that we walk across the room, we help 

 to make the dust which the housemaid sweeps up in the 

 morning. 



But it is not only the things around us which are being 

 thus continually rubbed and worn. Something of the 

 same sort happens to ourselves. We are perpetually 

 changing our skins, not indeed as the lizard does, but 

 piecemeal ; and, as the little loose particles are rubbed off, 

 they, too, help to make the dust which collects in our 

 houses, and needs to be constantly removed, if our bodies 

 are to be kept in a healthy state. 



For the greater part of this dust is organic ; it has at 

 one time or other formed part ot some organised living 

 thing, animal or vegetable, and, as such, it will burn 

 quickly if we set fire to it, or slowly if we spread it upon 

 the fields, and leave it, as we say, "to decay."* It 



* See Chap. xii. 



