94 APPLIED PHYSIOLOGY 



a hot summer's day the breathed air is of about the same 

 warmth as the air outside ; so there will be no current 

 unless the wind blows. This makes buildings very warm 

 and close in the summer. 



171. How to ventilate. When only one or two people 

 live in a room, the ventilation by cracks in the doors and 

 windows is enough and in very cold weather may be too 

 much. In new and very tightly built houses, the cracks 

 are few and small, and more ventilation will be needed. 



The simplest way to ventilate a room is to raise or lower 

 a window. But then the cold fresh air may blow on some 

 one's head and cause a cold. So you must be careful to- 

 open a window through which the wind will not blow. 

 Another way is to raise the lower window sash and fit a. 

 board to fill the opening. Then the fresh air will come in 

 between the two sashes and will make less of a draft. 



Some houses are heated by hot-air registers. If the air 

 in the register is pure, this will ventilate the room. Some- 

 times an opening is made in the chimney near the ceiling 

 so that the impure air can get out ; then more pure and 

 warm air will come in. In large buildings like schools and 

 theaters, there is often a fan run by machinery. This 

 forces out the impure air and fills the room with pure air. 

 So the air can be changed as fast as we wish. 



172. Sick rooms. It is very important to ventilate a 

 sick room, for sick persons need all the oxygen they can 

 get. They should not be disturbed with unpleasant odors. 

 Especially in some kinds of sickness, disease germs need 

 to be carried away as fast as they are given off. 



173. Bedrooms. Night air is exactly the same as air 

 in the daytime, except that it is cooler. Sleeping rooms- 

 should be as freely opened to the air at night as in the 

 daytime. The air of any room ought to be changed often 



