208 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH, 



body the warmth resulting from its combustion with the carbon con- 

 tained in the blood and tissues, and gives to the whole physical being 

 a vigor and freshness which is impossible where the element is 

 deficient. Thus to mankind it is life-giver, warmth-maker, and puri- 

 fier. Unlike food, which may be taken irregularly and at long inter- 

 vals, oxygen is a necessity at all times and in all conditions, in every 

 hour of the day and night; and upon its reaching or approaching the 

 normal quantity in the air around us, our health and enjoyment directly 

 depend. 



By the law of diffusion of gases, which causes the interchange of 

 position of gases separated by a thin porous partition, the carbonic acid 

 gas brought by the blood to the lungs passes out and is then exhaled, 

 while the oxygen breathed into the air cells passes in through the 

 walls of these cells to the blood. The heart sends the impure blood 

 derived from the circulation through the body to the lungs; this dark 

 blood is loaded with carbonic acid gas; the lungs return the aerated 

 and purified red blood through their blood vessels to another division 

 of the heart, which again drives the vivifying blood through the sys- 

 tem. Experiments have shown that a similar chauge in appearance 

 from dark to bright red blood can be caused by passing a stream of 

 oxygen through the dark venous blood of an animal. That a process 

 of combustion, or, otherwise put, chemical union, goes on at the same 

 time, is shown by the fact that the blood is raised one or two degrees 

 by its contact with oxygen. The oxygen in its course through the 

 body combines with the effete or waste products presented to it by the 

 tissues, and so the heating effect of combustion maintains the tempera- 

 ture of the whole body at the normal, about 98.0. The waste gases 

 given off by the lungs consist of carbonic acid gas, water vapor, and a 

 very small quantity of ammonia and other organic matters. 



The average volume of air breathed in at each breath is about 30 

 cubic inches, and the volume of air which may be easily breathed in by 

 an effort, and by expanding the chest, is about 130 cubic inches, or 

 about four times as much. After a very full inspiration about 230 cubic 

 inches can be expired by a man of average height and in good health. 

 The total capacity of the lungs, however, is much more than this — about 

 330 cubic inches. Thus in ordinary quiet breathing we only fill about 

 one-tenth of the available air space of the lungs. After every outbreath, 

 or expiration, a quantity of air is left in the lungs. This residual air 

 amounts to about 100 cubic inches. 



An adult at rest breathes about 086,000 cubic inches in the course 

 of twenty-four hours; a laborer at full work, about 1,586,900 cubic 

 inches — more than double. The amount of air passing into the lungs 

 has been estimated at 400 cubic feet in a state of rest, 600 in exercise, 

 1,000 in severe exertion. The number of air cells in the lungs is esti- 

 mated at 5,000,000 or 6,000,000, and their surface at about 20 square 

 feet. The epithelium or membranous film between the blood and air is 

 exceedingly thin, and in many parts the capillaries are exposed, in the 



