RESPIRATION. 589 



nature, and find their way into the expired air, are probably of a poisonous 

 nature. For it has been found that expired air is much more poisonous 

 to animal life than air which has not passed through the lungs of an 

 animal, but which contains the same amount of carbon dioxide and the 

 same degree of decrease of oxygen. It is, therefore, probable that these 

 organic substances which are removed from the lungs are poisonous, 

 rather than the carbon dioxide which accompanies them. 



The air which passes through the lungs actually decreases in volume 

 about one-fortieth or one-fiftieth of the amount taken in in inspiration, 

 this falling off being probably due to the fact that all the oxygen inspired 

 does not reappear as carbon dioxide, but enters into other compositions 

 in the body. 



The most striking contrast between expired and inspired air is in 

 the relative proportions of oxygen and carbon dioxide, while the nitrogen 

 undergoes but little change. The following represents this change: 



Oxygen. Nitrogen. Carbon Dioxide. 



Inspired air contains . . 20.81 79.15 .04 



Expired " . . .16.033 79.557 4.380 



The expired air, therefore, contains from 4 to 5 per cent, less 

 oxygen and 4 to 5 per cent, more carbon dioxide than the inspired 

 air. Taking thirty cubic inches as the amount of air taken in in each 

 inspiration in man, this will represent about one and one-half cubic 

 inches of oxygen. Supposing five hundred cubic feet to be taken in per 

 diem, the oxygen absorbed would amount to twenty-three cubic feet, or 

 one and one-third pounds, avoirdupois, oxygen. The amount of oxygen 

 varies according to different circumstances. 



The following conclusions give at a glance some principal sources 

 of variations. They will be studied more in detail under the subject of 

 Nutrition : 



A man in repose and fasting, with an external temperature of 90 F., 

 consumes 1465 cubic inches of oxj^gen per hour. 



A man in repose, fasting, with an external temperature of 59 F., 

 consumes 1627 cubic inches of oxygen per hour. 



A man during digestion consumes 2300 cubic inches of oxygen per 

 hour. 



A man, fasting, while he accomplishes the labor necessary to raise in 

 fifteen minutes a weight of seven thousand three hundred and forty-three 

 kilos to the height of six hundred and fifty-six feet, consumes 3814 

 cubic inches of oxygen per hour. 



A man, during digestion, accomplishing the labor necessary to raise 

 in fifteen minutes a weight of seven thousand three hundred and forty- 

 three kilos to the height of seven hundred feet, consumes 5568 cubic 

 inches of oxygen per hour. 



