RESPIRATION. 383 



Seat of Oxidation. It used to be held that the lungs were the 

 seat of the metabolic processes. Afterwards the seat of these chem- 

 ical changes was located in the tissues, the lungs playing but a small 

 part. Bohr has shown that about one-third of the metabolic phe- 

 nomena take place in the lung. He estimated the carbonic acid and 

 oxygen in the blood of the right heart, and compared these quantities 

 with those found in the blood of the left heart. He also measured 

 the quantity of blood passing through the lungs in a given time. 

 Knowing the amount of oxygen inhaled and the quantity of carbon 

 dioxide exhaled, he found that the lungs used up about one-third of 

 the oxygen and gave off one-third of the total carbon dioxide output. 



The temperature of the air expired is greater than that of the 

 air inspired, and is but a trifle lower than the body-temperature. 



Normal Food Supply. 



Fig. 141. Variations of Respiratory Quotient According to Food 

 Taken. ( LANGLOIS. ) 



Though the temperature of the surrounding atmosphere varies, that 

 of the expired air remains nearly the same. 



The volume of the air expired is greater than the volume of the 

 air inspired, by reason of the increase in temperature and the con- 

 tained watery vapor. If, however, it be dried and reduced to the 

 same temperature as the inspired air, there will be a diminution of 

 volume : about one-fiftieth. 



The respiratory quotient is the relation between the volume 

 of oxygen absorbed and the volume of carbonic acid eliminated. 

 That is : 



,. volume of C0 2 given off AT 



The respiratory quotient = Normally it is 



volume of absorbed 



M*=0.9. 



4.78 



This quotient varies, however, with the nature of the chemical 



