3 6o TEXT-BOOK OF PHYSIOLOGY. 



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 con- 

 taining barium or calcium hydrate. 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 atmos- 

 pheric air has been maintained for some time. From the percentage 

 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 10,800 or 12,- 

 240 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 :: 10,800 : x = 516 liters 

 Or 



ioo : 4.78 :: 12,240 : x = 585 liters. 



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

 either 473 or 526 liters; volumes in both instances which agree very 

 well with volumes obtained by other methods. 



From the fact that when one volume of oxygen combines with 

 carbon it gives rise to but one volume of carbon dioxid, it is evident 

 that of the oxygen absorbed the greater portion by far is utilized in 

 the oxidation of the carbon, while the smaller portion is utilized in 

 the oxidation of other substances, but especially hydrogen, as shown 

 by the increase in water eliminated beyond that consumed. These 

 amounts, however, are not fixed but variable, and depend on the 

 quality and quantity of the foods, exercise, 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 - -. 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 cent. This gain is probably of accidental occurrence, due to 

 absorption from the large intestine, in which decomposition of 

 nitrogen-holding compounds is taking place. (J It is generally believed 

 that free nitrogen plays no part in any phenomenon of combination 

 or decomposition within the body// 



The gain in watery vapor will depend on the amount previously 

 present in the air. This is conditioned by the temperature. I With 

 a rise in temperature the percentage of water increases; with' a fall, 

 it decreases. 1 By breathing into a vessel containing pumice stone 

 saturated with sulphuric acid, the vapor may be collected.^ The 

 difference observed between the weight before and after breathing 



