RESPIRATION. 401 



The results which have been obtained are represented in the following 

 table: 



Inspired Air. Expired Air. 



f Oxygen, 20 .80. 



ioo I Carbon dioxid, traces. 



vols. j Nitrogen, 79 .20. 



( Watery vapor, variable. 



Oxygen, 16.02. 



Carbon dioxid, . . 4.38. 



Nitrogen, 79 .60. 



Watery vapor, . . saturated. 



Organic matter. . a trace. 



These analyses indicate that under ordinary conditions the air loses 

 oxygen to the extent of 4.78 per cent, and gains carbon dioxid to the extent 

 of 4.38 per cent. ; that it gains in nitrogen to the extent of 0.4 per cent, and in 

 watery vapor from its initial amount to the point of saturation, as well as in 

 organic matter. It is to these changes in their totality that those disturbances 

 of physiologic activity are to be attributed which arise when expired air is 

 re-breathed for any length of time without having undergone renovation. 



Special forms of apparatus have been devised for the collection and analy- 

 sis of gases. Their construction as well as the methods of analysis involved 

 are complicated and need not be described in this connection. The presence 

 of the carbon dioxid, however, may be readily shown by breathing through 

 a glass tube into a vessel containing barium or calcium hydrate solution. The 

 turbidity which immediately follows is due to the formation of barium or 

 calcium carbonate, which can be due only to the presence of carbon dioxid. 

 That this turbidity is not due to the carbon dioxid normally present in the 

 air is shown by the fact that the solution remains clear until the passage of 

 the atmospheric air has been maintained for some time. From the percent- 

 age loss of oxygen and gain in carbon dioxid, the total oxygen absorbed and 

 carbon dioxid exhaled may be approximately calculated. Thus, if the 

 volume of air breathed daily be accepted at either 8,500 or 12,752 liters, and 

 the percentage loss of oxygen be 4.78, the total oxygen absorbed may be 

 obtained by the rule of simple proportion, e.g.: 



ioo : 4.78 :: 8,500 : # = 406 liters or 580 grams 1 

 Or 



ioo : 4.78 :: 12,752 : # = 609 liters or 870 grams. 



By the same method the total carbon dioxid exhaled is found to be either 

 372 liters or 735 grams, or 558 liters or 1103 grams; volumes in both instances 

 which agree very well with volumes obtained by other methods. 



From the fact that only 558 liters of carbon dioxid are exhaled as compared 

 with 609 liters of oxygen absorbed, it is evident that not all of the oxygen 

 unites with carbon to form carbon dioxid and that the remainder of the 

 oxygen must unite with some other element. As there is usually an excess 

 of water eliminated over that introduced into the body, it is highly probable 

 that the oxygen combines with free hydrogen to form water. The relative 

 amounts of the oxygen so utilized are not fixed but variable, and depend on 

 the quality and quantity of the foods, excercise, etc. The ratio of the 

 volume of the carbon dioxid exhaled to the volume of oxygen absorbed is 

 known as the respiratory quotient, and is usually represented by the symbol 



CO 



Q^ Thus in the foregoing analysis the respiratory quotient is 0.916. 



The gain in nitrogen is a variable factor, ranging from zero to 0.9 per 



1 i liter of oxygen weighs 1.4298 grams; i liter of carbon dioxid weighs 1.977 grams. 

 26 



