BIOLOGY APPLIED TO HEALTHFUL LIVING 527 



450. Ventilation. Frequent renewal of the air of build- 

 ings is required ; because the breathing of human beings and 

 the combustion in stoves, lamps, etc., use oxygen and add 

 carbon dioxide ; and because bacteria are carried in the dust 

 of the air. All systems of ventilation should provide for the 

 exit of the lighter warm air near the ceiling and the entrance 

 of fresh air (preferably warmed previously by heaters) near 

 the floor. At night when the body is properly protected in 

 bed the supply of fresh air may safely be very cold. The im- 

 portant rule is to get as much fresh air as possible without 

 chilling any part of the body by drafts. That is far more 

 harmful than poor ventilation, for " colds " are often pro- 

 duced ( 453). Good ventilation does not require that a high 

 wind constantly blow through a house. 



For accounts of the best methods of ventilation, see books 

 of hygiene and household science. The subject is so extensive 

 that only the great principles can be suggested here. 

 > 451. Avoiding Dust. Owing to the fact that dust often 

 carftes-ebngerous bacteria and that there is a harmful effect 

 of 'accumulated dust in the lungs, dust in the air should be 

 eliminated as far as possible from homes, factories, and public 

 buildings. Old-fashioned sweeping and dusting are dan- 

 gerous unless windows are opened and the wind allowed to 

 blow out the dust and bacteria. Carpet-sweepers and es- 

 pecially vacuum-cleaners are better. Damp cloths should 

 be used for wiping dust from furniture ; brushes and feather- 

 dusters are relics of the dark ages and should never be used. 

 If brooms must be used indoors, damp sawdust will help keep 

 dust from rising into the air. The most sanitary modern 

 dwellings have no carpets which are not easily taken outdoors 

 for cleaning, while the floors are painted, varnished, or waxed 

 so as to make washing easy and sweeping unnecessary. 



452. Artificial Breathing. This means causing the lungs 

 to respire after normal breathing has been stopped by im- 

 mersion in water or by gas asphyxiation. This can be done 



