DUST AND ITS DANGERS. 29 



the room, quickly resulted in sweeping away a 

 large proportion of the suspended micro-or- 

 ganisms. But this observer also found that 

 even very strong air currents were not able, 

 when sweeping over woollen and other fabrics, 

 carpets, hangings, etc., which had been be- 

 strewn with bacteria-laden dust, to free the 

 germs to any considerable extent from these. 

 The 'strong air currents carried off the sus- 

 pended particles, but those which had settled 

 on to the fabrics and floors were but little 

 affected. The practical bearings of this ob- 

 servation we shall see by and by. 



When we consider the constant tendency of 

 dust particles to settle as soon as they find 

 themselves in quiet places out of strong air 

 currents, and the fact that even ordinarily 

 efficient systems of ventilation do not carry off 

 any considerable proportion of the dust par- 

 ticles from closed still rooms, we are led to the 

 rather startling conclusion that the ordinary 

 living-rooms, even though they be well ven- 

 tilated, are actually dust and bacteria reposi- 

 tories, and that when by a system of forced 

 ventilation we cause large volumes of dust- 



