MECHANISM AND CHEMISTRY OF RESPIRATION 209 



gas which is in itself undesirable. Such methods of warming a 

 room are hygienically bad. When heated air is sent into a 

 room from a furnace in the cellar it will produce good ventila- 

 tion provided there is some ready outlet for the air of the room. 

 Heating a room by a radiator, either hot water or steam, 

 simply warms the air already present and furnishes no proper 

 outlet for the stale air, often making the use of special venti- 

 lators a necessity. 



3. The greater the difference in temperature between the 

 air in a room and that outside, the easier it is to produce 

 currents of air. In cold weather air comes in and goes out 

 through cracks around doors and windows much more rapidly 

 than it does in warm weather. 



4. The rooms of an ordinary house are so large in pro- 

 portion to the few people living in them that no attention 

 need be given to ventilation except perhaps in very cold 

 weather when they are more closely shut. 



5. Sleeping rooms should be more carefully ventilated 

 than living rooms. But most care is needed in schoolrooms 

 and similar places, where many people are gathered together. 



6. Expired air is warmer than the ordinary air of a room, 

 and rises at first. As it cools, however, it sinks, because 

 it is heavier than the rest of the air on account of the 

 presence of carbon dioxid. Hence, while ventilators at the 

 top of a room will take away the warmed air, there should 

 also be ventilators low down to carry off the heavier gasee 

 after they have cooled and sunk to the floor. 



Treatment in Cases of Suffocation. There are many kinds 

 of accidents that result in the exclusion of air from the lungs, 

 or asphyxia as it is called, producing suffocation. In all cases 

 the first thing to be done is to remove the cause of the trouble. 

 If it be choking from compression at the throat, free the 

 throat from whatever constricts it; if it be breathing poison- 

 ous gases, remove the patient to fresh air; if it be water, as 

 in the most common cases of drowning, lift the patient by 



