184 



RESPIRATION AND EXCRETION 



Natural ventilation. Air finds a way of entrance 

 into most of our rooms. 



door air through cracks, window casings, chimney hearths, opening 

 doors, etc., is often enough to change the air in rooms not con- 

 stantly used, it becomes necessary to use other means in schools 

 and other crowded buildings. From 2000 to 3000 cubic feet of air 



is considered as the need 

 of the average person 

 each hour ; and various 

 devices for changing the 

 air frequently are in use. 

 In schools air is often 

 drawn in by fans, washed 

 to remove dust and bac- 

 teria, and then forced 

 through ducts into the 

 rooms, the used air pass- 

 ing out through other 

 ducts. Windows open a 

 short distance at top and 

 bottom are the best means of ventilation for the house. A board 

 should be placed in front of the open space to prevent direct drafts, 

 for strong drafts chiU the skin, with a consequent congestion of 

 blood vessels and possible cold. 



A temperature of not more than 68° F. is most favorable for 

 mental work. It is found that during the winter, when artificial 

 heat is used, the air becomes too dry. Various devices, the simplest 

 of which are pans of water on registers or radiators, evaporate 

 moisture and raise the humidity content of the air somewhat, but 

 no effective device is in general use for keeping the humidity 

 equal to that of the outside air. Consequently, when we go from a 

 warm, dry room into a cool, out-of-door air, the skin becomes 

 chilled and we may take cold. 



Ventilation of Sleeping Rooms. — Sleeping in badly ventilated 

 rooms is the cause of much discomfort and often of illness. Beds 

 should be placed so that a constant supply of fresh air is given 

 without a direct draft. This may often be managed with the use 

 of screens. Bedroom windows should be kept open for a time in 

 the morning to allow free entrance of the sun and air, bedclothes 

 should be washed frequently, and sheets and pillow covers often 



