228 



APPLIED PHYSIOLOGY 



in a room, the natural cracks and openings are not suffi- 

 cient, but other openings must be made. 



399. Methods of ventilation. -< In ventilation a per- 

 ceptible current of air must be avoided, for many people 

 easily take cold when a single part of the body is cooled 



Diagram of the natural ventilation of a room. 



The arrows indicate the direction of the air currents. 



as by a draft. The air of a room can be changed only 

 three times an hour without producing noticeable drafts 

 throughout the room. 



Many devices have been used to secure an even distribution of the 

 incoming fresh air. The simplest is to lower the upper window sash. 

 Warm air will pass out above the upper sash, while the cooler fresh air 

 will enter between the two sashes, and will be given an upward direc- 



