THE CHEMISTRY OF RESPIRATION 1071 



altered by increasing the percentage of carbon dioxide and of oxygen 

 respectively. It will be seen in each, case that there was a corresponding 

 alteration of the tension in the arterial blood, the tension of carbon dioxide 



230 *o so 



20 30 'tO 50 If tO 2O 30 



FIG. 503. Tensions of 2 and C0 2 in alveoli compared with those in arterial 



blood of rabbit. 



The dotted lines represent the tensions in the alveolar air, the uninterrupted 

 lines the tensions of the gases in the arterial blood. (KROGH.) 



being higher and that of oxygen lower in the blood than in the air throughout 

 the experiment. We have no direct determinations of the tensions of the 

 gases in the blood of man, though an approximate valuation of these tensions 



2095 



in inspired 

 air 



f30 



50 3 10 



FIG. 504. Tensions of gases in alveolar air and in arterial blood. 

 A, during artificial increase of oxygen tension in alveoli ; B, during artificial 



~C( 



increase of 



tension in alveoli. 



can be obtained by knowing the degree to which the arterial and venous 

 blood respectively are saturated with oxygen or carbon dioxide. An indirect 

 method may be employed to measure the gaseous tensions in the venous 

 blood coming to the lungs. It is possible, as Loewy has shown, to block the 



