138 HUMAN BIOLOGY 



without causing a direct draught. In order to secure a 

 proper circulation of air an opening of equal size should be 

 provided by lowering the top sash of the window. 



Furnace heat is much more satisfactory than steam from 

 the point of view of ventilation, for in this way a continual 

 supply of fresh, warm air may be furnished. An open fire- 

 place is one of the best means of removing foul air, and when 

 a fire is burning, a strong current up chimney is assured. We 

 have called attention to the fact that dry heat tends to cause 

 catarrh and other diseases of the air passages. Provision 

 should therefore be made to keep the air in rooms moist. 

 This may be partially accomplished by keeping the water 

 pans in a furnace full of water, or by leaving trays of water 

 on steam or hot water radiators. 



