200 RESPIRATION 



in proportion to the number of air consumers, the principal 

 object will be attained. Thus, a door and window, each open- 

 ing into the outer air, will ordinarily ventilate a small apart- 

 ment ; or a window alone will answer, if it be open both above 

 and below, and the open space at each end be not less than one 

 inch for each occupant of the room, when the window is about 

 a yard wide. The direction of the current is generally from 

 below upward, since the foul, heated air tends to rise ; but this 

 is not essential. * Its rate need not be rapid ; a " draught," 

 or perceptible current, is never necessary to good ventilation. 

 The temperature of the air admitted may be warm or cold. It 

 is thought by many that if the air is cold, it is pure ; but this 

 is an error, since cold air will receive and retain the same 

 impurities as warm air. 



44. Shall we open our bed-rooms to the night air ? Florence 

 Nightingale says, in effect, that night air is the only air we 

 can then breathe. "The choice is between pure air without 

 and impure air within. Most people prefer the latter an 

 unaccountable choice. An open window, most nights in the 

 year, can hurt no one. In great cities, night air is the best 

 and purest to be had in twenty-four hours. I could better 

 understand, in towns, shutting the windows during the day 

 than during the night." (Read Note 11.) 



* When the window is of the common sash kind, a good supply of 

 fresh air may be obtained without a current, by placing a strip of board 

 about four inches wide under the lower sash (Fig. 53). The window is 

 thus closed against rain and snow, but allows of a supply of fresh air to 

 enter between the sashes. If still more ventilation is needed to keep the 

 air of the room sweet, the same arrangement may be made at the top of 

 the window. 



11. Pure Air in our Homes during Cold Weather. "Fresh air is the 

 great natural disinfectant, antiseptic, and purifier, and not to be com- 

 pared for a moment with any of artificial contrivance. There is plenty of 

 it in the world ; yet, disguise the fact as we may, there is no getting over 

 the unwelcome truth, that to provide it in abundance in our climate is 

 expensive, since during seven months in the year it must be artificially 

 warmed, in order that our homes may be comfortable. To take in air at 

 the average winter temperature of 28, raise it to 68, and discharge it 



44. State what Florence Nightingale says about inhaling night air. 



