HEAT IN RELATION TO THE HUMAN BODY 13 



3. To secure desired changes of air in rooms of a build- 

 ing provided with air-shafts, but without fans or other 

 devices for forcing air into and out of rooms, what must 

 be true at all times (a) of the relative temperatures of 

 air at inlet and outlet ; (6) of the place for outlet that no 

 warmed air escape without yielding for use its oxygen; 

 (c) of the place of inlet that the cold air be warmed 

 before it spreads through the room? What devices may 

 be employed to break up an incoming cold air current and 

 divert it upward? 



4. Hold a lighted candle (a) at the top of an open door- 

 way; (b) down at the floor. Repeat the tests at narrow 

 openings made by lower- 

 ing the upper sash of a 



window, and raising the 

 lower one. What ob- 

 jections are there to ven- 

 tilating rooms in either 

 of these ways in cold 

 weather ? 



5. Why is there need 

 of special attention to 

 the ventilation of our 

 sleeping rooms ? How 

 may this be provided 

 even in the coldest 



weather? What are some of the results of inattention to 

 ventilation of sleeping rooms? What is the change in com- 

 position of the air of a room where gas lights or oil stoves 

 are kept burning? 



FIG. 7. A victim of oxygen starvation 

 becomes an easy prey for tuberculosis 

 or other germ diseases. 



