138 ANATOMY FOR, NURSES. [CHAP. XII. 



2. However dry the external air may be, the expired air is 

 quite, or nearly, saturated with moisture. 



3. The expired air contains about four or five per cent less 

 oxygen, and about four per cent more carbonic acid than the 

 external air, the quantity of nitrogen suffering but little change. 

 Thus: 



Oxygen. Nitrogen. Carbonic Acid. 



Inspired air contains . . . 20.81 79.15 0.04 



Expired air contains . . . 16.033 79.587 4.38 



(Foster.) 



In addition the expired air contains a certain amount of effete 

 matter, of a highly decomposable and impure character. The 

 quantity of water given off in twenty-four hours varies very 

 much, but may be taken on the average to be about nine ounces. 

 The quantity of carbon given off at the same time is pretty 

 nearly estimated by a piece of pure charcoal weighing eight 

 ounces. 



If a man breathing fifteen to sixteen times a minute takes in 

 thirty cubic inches of air with each breath, and exhales the 

 same quantity, it follows that in twenty-four hours from three 

 hundred and fifty to four hundred cubic feet of air will have 

 passed through his lungs. And if such a man be shut up in a 

 close room measuring seven feet each way, all the air in the 

 room will have passed through his lungs in twenty-four hours. 



Since at every breath the external air loses oxygen and gains 

 carbonic acid and other waste and poisonous matters, it is 

 imperative that some provision be made for constantly renewing 

 the atmospheric surroundings of people in dwelling houses. 

 This is accomplished by ventilation, which consists of a system 

 of mechanical contrivances, by means of which foul air is con- 

 stantly removed and fresh air as constantly supplied. 



The minimum amount of air space every individual should 

 have to himself is 800 cubic feet (a room nine feet high, wide, 

 and long contains 729 cubic feet) and this space should be 

 accessible by direct or indirect channels to the outside air. 



Effects of respiration upon the blood. While the air in passing 

 into and out of the lungs is robbed of a portion of its oxygen 

 and loaded with a certain quantity of carbonic acid, the blood 

 as it streams along the pulmonary capillaries is also undergoing 

 important changes. As it leaves the right ventricle it is venous 



