HYGIENE OF RESPIRATION 



173 



293. Some persons in their anxiety for pure air become 

 extremists, and forget that the body may likewise be in- 

 jured by cold. In ventilating a room, not one but two 

 purposes must be kept in view : to furnish air that is pure, 

 and air at the proper temperature. 



294. Methods of Ventilation depend upon the principle 

 that hot air is lighter than cold air and is pushed up by 

 it. If you have two openings for ventilation, one higher 

 than the other, at which opening does the warm air 

 go out ? If the 



higher opening 

 is near the ceil- 

 ing, do the per- 

 sons in the room 

 get the coldest or 

 the warmest air? 

 Does such a 

 method econo- 

 mize the fuel? 

 If the inlet is 

 near the floor, 

 why should the 

 stove be near 



FIG. 147. The Proper Method of ventilating a Room. 



The stove is on the side toward the cold winds. The inlet is 

 near the stove, the outlet farthest away. If the window near 

 the stove were lowered from the top, what would probably 

 happen? If another window near the stove were opened, 

 what might happen? If the prevailing cold winds came from 

 the opposite direction, what changes should be made in the 

 room? How do you ascertain whether the outlet fails to serve 

 its purpose and becomes an inlet? 



the inlet ? Why should the outlet be on the side of the 

 room farthest from the stove ? 



295. Good ventilation is arranged so that the fresh air 

 shall be heated before or just after it enters the room, and 

 that it shall pass across the room in order that the in- 

 mates may get the benefit of both its warmth and its purity 

 before it passes out (Fig. 147). Test the direction of the 

 air currents in your bedroom and in your schoolroom by 

 means of a spider web hanging from the end of a stick. 

 Why is it best not to have the outlet on the side of the house 

 toward the prevailing wind in winter ? If the inlet is so 

 situated that the cold air does not pass over the stove, a 



