4 HOUSEHOLD BACTERIOLOGY. 



comes through open doors and windows. Few win- 

 dows and doors are so tightly fitted that fine dust will 

 not sift in round their casings, 

 ingredients Until electricity is made the common source of heat 



of Dust - 



and light, there will be much dust from coal and wood, 

 both before and after they are burned. These sources 

 are too evident to need more than a mention. It is 

 from the wear and tear of the house itself, its finish and 

 furnishings, from our own bodies and the clothing that 

 covers them, that the larger amount of dust comes. 

 From these we have bits of wood, stone, cotton, hair, 

 dead cells from all animal bodies a mass of mineral, 

 animal, and vegetable matter of very complex compo- 

 sition. 



Since time began, everything in this old world has 

 thus been wearing away more or less slowly, adding 

 bit by bit to similar accumulations, until what we 

 know as soil has been built up pure mineral soil made 

 from the debris of the rocks ; organic soil or loam from 

 the addition to this mineral soil of vegetable and ani- 

 mal debris. The same processes are continually going 

 on all about us. 



The dictionaries recognize this process when they 

 tell us that dust is "Earth or other matter in fine dry 

 particles so attenuated that they can be raised and car- 

 ried by the wind." 



M of m Dust Winds then are the responsible agents for much of 

 the dust in our houses, but wind is simply air in mo- 

 tion. We cannot walk across the floor, make a bed, 

 rock comfortably in a chair, or dance a jig without 



