8 4 



HUMAN BIOLOGY 



question in cold weather is because the air furnished must 



be not only pure, but warm. To keep cold air out often 



means to keep foul air in. Heating with Jiot air, by which 



system pure air is passed over 

 a furnace, and fresh air con- 

 stantly admitted, may be a good 

 method (Figs. 80, 81), but is 

 often a dismal failure because 

 it dries out the air, which in 

 turn dries out the skin. To 

 prevent this, wide vessels of 

 water should be set at the in- 

 lets. Dry air is cooling. Why ? 

 Dr. Barnes proved that moist 

 air at 65 is as comfortable as 

 dry air at 71. Air saturated 

 with vapor at 60 will only be 

 50 per cent saturated at 80. 

 Such air dries out the mucous 

 membrane of eyes, nose, and 



throat. Heating by hot water circulating in pipes, or by 



steam, gives no means of 



introducing fresh air, and 



is likely to cause worse 



ventilation than any other 



method. The radiators 



should stand close to win- 

 dows or other fresh-air inlet, 



that the air may be heated 



as it enters, and the outlet 



for air should be farthest 



FIG. 81. The air enters through 

 a special inlet and is warmed 

 as it passes through hood sur- 

 rounding the stove. 



FlG. 82. Chimney with a passage be- 

 hind fireplace, or grate, in which the 

 air is warmed as it enters. 



from the radiators. The same rules apply to heating by 

 stoves. An oil stove for heating is an inconceivable 



