416 THE HUMAN BODY 



well-being requires that the air that we breathe be reasonably 

 pure also. Provisions for renewing the air of occupied rooms 

 must not be neglected, therefore, in working out ventilation plans. 



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 

 readily demonstrated. If a rabbit be rendered unconscious by 

 chloroform, and its chest be opened, after a pair of bellows has 

 been connected with its windpipe, it is seen that, so long as the 

 bellows are worked to keep up artificial respiration, the blood in 

 the right side of the heart (as seen through the thin auricle) and 

 that in the pulmonary artery, is dark colored, while that in the 

 pulmonary veins and the left auricle is bright red. Let, however, 

 the artificial respiration be stopped for a few seconds and, conse- 

 quently, the renewal of the air in the lungs (since an animal can- 

 not breathe for itself when its chest is opened), and very soon the 

 blood returns to the left auricle as dark as it left the right. In a 

 very short time symptoms of suffocation show themselves and the 

 animal dies, unless the bellows be again set at work. 



In a former paragraph (p. 412) we saw that about 5 volumes in 

 100 of oxygen are absorbed from the alveolar air into the blood, 

 and 4.4 in 100 of carbon dioxid given off to the alveolar air from the 

 blood. If we put the amount of air inhaled and exhaled with each 

 breath (tidal air) at 500 c.c. and the respiratory rate at 15 per 

 minute, we have 7,500 c.c. of air involved each minute, 5 per cent 

 of this, or 375 c.c. would give the oxygen consumption and 4.4 

 per cent, or 330 c.c. the carbon dioxid output in the same time. 

 As a matter of fact direct determinations of the oxygen absorp- 

 tion and the carbon dioxid output of persons at rest ordinarily 

 give somewhat smaller figures than these, 280-325 c.c. per minute 

 for oxygen and 250-280 c.c. for carbon dioxid. This discrepancy 

 can be explained by recalling that the figures for tidal air, for the 



