METHODS OF* MEASURING RESPIRATORY EXCHANGE 37 



In the Jaquet apparatus, and in practically all the air-current ap- 

 paratus presently to be described for studying the pulmonary re- 

 spiration, the outgoing or expired air only is measured. In order to 

 calculate the absorption of oxygen it is necessary in this case to as- 

 sume that no other gas than oxygen and carbon dioxide is involved 

 in the respiratory exchange, an assumption which is practically justified 

 in almost all cases (see p. 53). On the basis of this assumption the 

 ingoing quantity of air (I) can be calculated from the outgoing (E), 



FIG. ii. Diagram of Grafe's respiration apparatus. 



and the percentages of nitrogen in the ingoing (Nj) and outgoing (N E ) 

 air respectively. We have 



ioo 



E - E or I 

 ioo 



E ?. 



The oxygen percentages in the ingoing and outgoing air being de- 

 noted Oi and O E respectively the oxygen absorption is 



I .0.. .. -* 



IOO " IOO 



or (5 o, - O E Y 



ioo VN, 7 



^p Oi, the percentage of oxygen in the ingoing air multiplied by 



the ratio between the nitrogen percentage in the outgoing and ingoing 

 air, is called the corrected oxygen percentage. 



