DUST AND BACTERIA. 129 



2. Air in rooms needs constant renewal. 



3. Grates are good ventilators, but not economical heaters. Grates 

 heat very unevenly. 



4. Stoves are economical heaters, but poor ventilators. Stove heat 

 is also very uneven. 



5. All crowded rooms, as schoolrooms and churches, need special 

 inlets for fresh air and outlets for foul air. 



6. The most common means of withdrawing the air is by foul-air 

 shafts. Heat is the force relied on, but the removal of foul air is usually 

 inadequate, on account of the slowness of the current or the narrowness 

 of the outlet, or both combined. 



7. Fans are much more certain to be effectual. 



8. Steam and hot water may heat directly (by radiation) or indi- 

 rectly (placed in flues). A combination of direct and indirect heating 

 favors economy and efficiency. 



9. Dust as mere dry dead matter is irritating. 



10. Disease germs may form part of the dust of the air. 



1 1 . Most of our contagious diseases are known to be due to bacteria. 



12. Burning is the surest method of destroying germs. 



13. Carpets, tapestries, and cloth-upholstered furniture add largely 

 to the dust in houses. 



14. Putrefaction is caused by bacteria. 



15. Preservation of food depends on destroying, or excluding, or 

 retarding the growth of the bacteria of putrefaction . 



Questions. i . How can we renew the air of a room without having 

 unpleasant drafts ? 



2. Should bedroom windows be open at night? Is night air bad? 



3. What dangers in the use of hard coal? 



4. Should there be a damper in the smoke pipe of a hard coal 

 stove? 



5. What do miners mean by " choke damp " ? 



6. What is hay fever? Asthma? Bronchitis? Pneumonia? 



7. Compare stove and furnace heating. 



8. Compare heating by steam and by hot water. 



9. Is the air in the mountains or on the seashore better than else- 

 where ? 



10. What regions are recommended for consumptives ? Why? 



