138 HEATING AND VENTILATION. 



ing a sedentary pursuit, it is necessary to heat the air for a 

 considerable part of the year. When one is actively exercis- 

 ing his muscles he may keep warm outdoors through our 

 winter days. But, as we see, the heat of the body depends 

 on its internal fires, the oxidation of its tissues. 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. We must have a constant renewal of 

 air or we suffer greatly. One serious trouble is that many 

 cannot afford (or think they cannot) to heat the air properly, 

 and many others are ignorant concerning these matters. 



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 compar- 

 atively small space, as in many public buildings. But in our 

 private dwellings, even when the owners are amply able to 

 secure the most sanatory appliances, defective apparatus is 

 often put in. Any system that does not provide for a constant 

 renewal of the air is defective. 



Grates will aid largely in renewing the air. Although in 

 themselves they merely have provision for sending radiant 

 heat out into the room and much air up the chimney, yet, 

 without any special provision for inlet of air to the room, 

 they draw air in through every crack and crevice. It would 

 probably be very much better to have special ducts for the 

 admission of air which is suitably warmed while on its way 

 into the room, and to make the doors shut snugly, and to have 

 double windows, as then both the admission of fresh air and 

 the regulation of heat will be better secured. But it is a 

 serious question whether, with all our modern appliances and 

 conveniences and luxuries, uniform heat, electric and other 

 regulators whether, on the whole, we have better air in 



