1 70 



BIOLOGY AND HUMAN LIFE 



In artificially heated houses there is often danger of having 

 the air too dry, since the air coming from the outside contains 

 but a fraction of the moisture which it may hold after it be- 

 comes warmed. Special efforts must be 

 made to insure enough moisture. 



3. Movement. The air next to the skin 

 soon becomes saturated with moisture 

 and nearly as warm as the body itself. 

 If this air is allowed to remain next to 

 the skin undisturbed, we soon become 

 very uncomfortable. Where there are 

 large rooms and windows, and not too 

 many occupants in a room, the natural 

 movement of the air will be sufficient 

 (see Fig. 89). When many people have 

 to be in a room, as in schools and work- 

 shops (especially in winter, when arti- 

 ficial heating is necessary and windows 

 are likely to be closed), there is need of 

 special attention to ventilation, and forced 

 ventilation may become necessary. It is 

 often found desirable to use an electric 

 fan to insure movement of the air, even 

 when there is no change in the amount 

 or quality of the air. 



Many people fear drafts as though the mere 

 movement of the air were dangerous. What is 

 dangerous about a draft is the sudden chilling 

 of the skin, with a resulting congestion of the 

 blood vessels. In general, chilling the body 

 lowers the resistance to infection (see page 339). 

 By means of cold baths most of us can accustom the skin to react vigor- 

 ously to rapid changes in temperature. 



140. Suffocation and drowning. When the gas exchange in 

 the air sacs of the lungs is stopped for several minutes, suffoca- 

 tion takes place, and death may result. Suffocation may be due 



Fig. 89. Window ven- 

 tilation in cold weather 



So long as weather per- 

 mits, ventilation should be 

 by means of windows, open 

 at top and bottom for the 

 freest possible circulation 

 of air. In cold weather 

 a window board placed 

 under the lower sash pre- 

 vents drafts and allows 

 circulation between the 

 sashes and the top 



