CHAPTER XI. 

 VENTILATION AND HEATING. 



Need of Proper Ventilation. When one is actively 

 exercising he may keep warm outdoors even on a cold 

 winter day. For the heat of the body depends on its 

 internal fires, the oxidation of its tissues. But if we are 

 inactive, these fires burn feebly, and we need outside heat. 

 While air is free, it really costs a good deal of money to 

 have it properly warmed. 



A Lack of Effective Systems of Ventilation. Lung 

 diseases are rare in the regions where the windows and 

 doors may be kept open most of the days of the year. It 

 is from shutting ourselves in so closely that we suffer. 

 This is especially true where many people are housed in a 

 comparatively small space, as in many public buildings. 

 But in our private dwellings, even when the owners are 

 amply able to secure the best appliances, defective appa- 

 ratus is often put in. Any system that does not provide for 

 a constant renewal of the air is defective. 



The General Principles of Ventilation. Of the forces 

 that renew the air of rooms two are natural, (i) diffusion 

 and (2) the wind ; and two are artificial, (3) warm air shafts 

 and (4) fan systems. 



Diffusion. Gases tend to mix. We know that if a 

 bottle containing an odorous substance is opened in a 

 room where there are no air currents the odor tends to 



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