RESPIRATION 95 



double process that of bringing fresh air into the room 

 and that of getting rid of air that has been rendered impure 

 by breathing 1 or by lamps. Outdoor air is usually of a 

 different temperature (colder in winter, warmer in summer) 

 from that indoors, and as a consequence differs from it 

 slightly in weight. On account of this difference, suitable 

 openings in the walls of buildings induce currents which 

 pass between the rooms and the outside atmosphere even 

 when there is no wind. In winter care must be taken to 

 prevent drafts and to avoid too great a loss of heat from 

 the room. A cold draft may even cause more harm to 

 one in delicate health than the breathing of air which is 

 impure. To ventilate a room successfully 

 the problem of preventing drafts must be 

 considered along with that of admitting the 

 fresh air. 



The method of ventilation must also be 

 adapted to the construction of the building, 

 the plan of heating, and the condition of 

 the weather. Specific directions cannot be 

 given, but the following suggestions will be 

 found helpful in ventilating rooms where FIG. 46. Win- 

 the air is not warmed before being admitted : dow adjusted for 



1. Introduce the air through many small ventilation with- 

 openings rather than a few large ones. If 



the windows are used for this purpose, raise the lower sash 

 and drop the upper one slightly for several windows, vary- 

 ing the width to suit the conditions (Fig. 46). By this means 

 sufficient air may be introduced without causing drafts. 



2. Introduce the air at tlie warmest portions of the room. 



1 Not only do the lungs remove oxygen from the air and add carbon dioxide to 

 it, but they separate from the body considerable moisture and, according to some 

 authorities, a small amount of an impurity referred to as " animal matter." Odors 



