256 THE HUMAN BODY. 



lowered tone of the whole body, less power of work, physi- 

 cal or mental, and less power of resisting disease. The ill 

 effects may not show themselves at once, and may accord- 

 ingly be overlooked or considered scientific whims by the 

 careless, but they are there ready to manifest themselves 

 nevertheless. 



In order to have air to breathe in a fairly pure state 

 every man should have for his own allowance at least about 

 800 cubic feet of space to begin with, and the arrangements 

 for ventilation should at the very least renew this at the 

 rate of one cubic foot per minute. The nose is, however, 

 the best guide, and it is found that at least five times this 

 supply of fresh air is necessary to keep free from any odor 

 the room inhabited by one adult. If an inhabited room 

 smells " close" to one coming into it from "out of doors," 

 the air 5n it is unwholesome to breathe for any length of 

 time. 



How to Ventilate. Ventilation does not necessarily 

 mean draughts of cold air, as is too often supposed. In 

 warming by indirect radiation it may readily be secured by 

 fixing, in addition to the registers from which the fresh 

 warmed air reaches the room, corresponding openings at 

 the opposite side by which the old air may pass off to make 

 room for the new. An open fire in a room will always 

 keep up a current of air through it, and is one of the 

 most wholesome, though not most economical, methods of 

 warming an apartment. 



Why are the injurious effects of impure air npt to "be ignored? 



What volume of air should be allowed to each adult? At what 

 rate should it be replenished? What supply of fresh air is needed to 

 keep an inhabited room free from odor? Is it safe to live in a room 

 which " smells close"? 



How may ventilation be secured in heating by " indirect radia- 

 tion"? What are the advantages and what the disadvantages of an 

 open fire? 



