RESPIRATION: THE GASEOUS INTERCHANGE 375 



though not the most economical, method of warming an apart- 

 ment. 



Stoves in a room, unless constantly supplied with fresh air 

 from without, vitiate its air to an unwholesome extent. If no 

 appliance for providing this supply exists in a room, it can usually 

 be got, without a draught, by fixing a board about four inches 

 wide under the lower sash and shutting the window down on it. 

 Fresh air then comes in by the opening between the two sashes 

 and in a current directed upwards, which gradually diffuses itself 

 over the room without being felt as a draught at any one point. 

 In the method of heating by direct radiation (steam or hot water), 

 the apparatus employed provides of itself no means of drawing 

 fresh air into a room, as the draught up the chimney of an open 

 fireplace or of a stove does; and therefore special inlet and outlet 

 openings are very necessary. 



In severe weather, when there is a tendency to keep rooms 

 rather tightly closed, a good plan is to ,open widely all doors and 

 windows for a few minutes each day, allowing fresh air to penetrate 

 to every corner, sweeping out the old air before it. This daily 

 renewing, helped out by such ventilation as is afforded by ill- 

 fitting doors and windows, usually keeps the air of rooms in 

 respirable condition when not occupied by too many persons. 

 The modern habit of sleeping summer and winter in rooms with 

 open windows is to be highly commended, and should be even 

 more generally adopted. In fact the more outdoor air one can 

 have, and at the same time keep warm, the better for the bodily 

 well-being. The beneficial effects of fresh air and sunshine, 

 especially in pulmonary tuberculosis, cannot be too strongly 

 emphasized. 



Changes undergone by the Blood in the Lungs. These are the 

 exact reverse of those undergone by the breathed air what the 

 air gains the blood loses, and vice versa. Consequently, the blood 

 loses heat, and water, and carbon dioxid in the pulmonary capil- 

 laries; and gains oxygen. These gains and losses are accompanied 

 by a change of color from the dark purple which the blood ex- 

 hibits in the pulmonary artery, to the bright scarlet it possesses in 

 the pulmonary veins. 



The dependence of this color change upon the access of fresh 

 air to the lungs while the blood is flowing through them, can be 



