154 RESPIRATION 



the lungs, it is well known that odorous emanations proceed 

 from them after garlic, onions, turpentine, alcohol, certain 

 drugs, etc., have been taken into the stomach. 



Relation Between Oxygen Consumed and Carbon Dioxide 

 Exhaled. A given volume of O will combine with carbon 

 to form the same volume of CO ; or the amount of O in a 

 given volume of CO is equivalent to that volume when set 

 free from the carbon. A cubic foot of O will unite with 

 carbon to form a cubic foot of CCte; or a cubic foot of 

 CO2 will yield, on dissociation, a cubic foot of O. 



This being the case, if all the O consumed in the lungs 

 were exhaled therefrom in the form of CO, the amount of 

 CO exhaled would just equal the amount of O consumed. 

 But the amount of consumed O is about 5 per cent, of the 

 inspired air, while the amount of exhaled CO is only about 

 4 per cent, of the expired air. It follows, therefore, that I 

 per cent, of the volume of inspired air is not represented by 

 the CO2 exhaled from the lungs and skin. The relation be- 

 tween the consumed O and the exhaled COv is usually ex- 

 pressed as the "respiratory quotient" the division of the 

 latter by the former giving the quotient. This quotient is 

 made to vary by many circumstances, though for any con- 

 siderable period its average is about the same. 



While it has been stated that the O absorbed and the CO2 

 produced vary together usually, they are in a certain meas- 

 ure independent of each other. For CO does not result 

 from the immediate union of O with carbon of the carbo- 

 hydrates and fats, but may be stored in the shape of com- 

 plex compounds, which may later split up with the formation 

 of CO2, either by oxidation or by intramolecular cleavage. 

 Furthermore, more O is necessary to oxidize (that is, to 

 form carbon dioxide) some molecules than others. A fat 

 requires considerably more O to produce CO2 than does a 

 carbohydrate; so that the kind of food in store would 

 also affect the respiratory quotient. 



With respect to the O which, in the long run, is not repre- 



