CHAPTER V 



CHANGES WHICH THE AIR AND THE BLOOD UNDERGO IN 



RESPIRATION 



Composition of the air Consumption of oxygen Exhalation of carbon dioxide Influence 

 of age Influence of sex Influence of digestion Influence of diet Influence of 

 muscular activity Influence of moisture and temperature Influence of the season of 

 the year Relations between the oxygen consumed and the carbon dioxide exhaled 

 Sources of carbon dioxide in the expired air Respiratory quotient Exhalation of 

 watery vapor Exhalation of ammonia, organic matter etc. Exhalation of nitrogen 

 Changes of the blood in respiration Analysis of the blood for gases Nitrogen of the 

 blood Oxygen of the blood Carbon dioxide of the blood Respiration by the tissues 

 Respiratory efforts before birth Asphyxia. 



CHANGES OF THE AIR IN RESPIRATION 



Composition of the Air. Pure atmospheric air is a mixture of 79.05 

 parts of nitrogen with 20.95 parts of oxygen. Dewar and others, how- 

 ever, have discovered in the air a small quantity of hydrogen, with new 

 elements called argon, metargon, neon, xenon and helium, all to be in- 

 cluded in the proportion assigned to nitrogen. The air usually contains 

 in addition about one part in two thousand of carbon dioxide. The air 

 is never free from moisture, which is variable in quantity, being usually 

 more abundant at a high than at a low temperature. Floating in the 

 atmosphere are large numbers of minute organic bodies, and various 

 odorous and other gaseous matters are accidental constituents. 



It is necessary to the regular performance of respiration that the air 

 should contain about four parts of nitrogen to one of oxygen and should 

 have about the density that exists on the surface of the earth. When 

 the density is much increased, as in mines, respiration is more or less 

 disturbed. Under great pressure, such as exists in caissons, a quantity 

 of nitrogen which is sparingly soluble under ordinary conditions 

 may be forced into the blood. Return to the outer air should be gradual ; 

 for if the excessive pressure is suddenly removed, bubbles of nitrogen 

 may be rapidly disengaged, often with a fatal result. Exposure to a 

 rarefied atmosphere, as in the ascent of high mountains or in aerial 

 voyages, may seriously disturb respiration, from the fact that less oxygen 

 than usual is presented to the respiratory surface and the reduced 

 atmospheric pressure diminishes the capacity of the blood for retaining 



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