RESPIRATION 



265 



air, and the percentage of oxygen in it determined by the vacuum 

 pump or the differential blood gas apparatus. Charts are thus pre- 

 pared in which the amounts of oxygen combined at different pressures 





10 20 



100^ 



mm. pressure 



FIG. 137. CYLINDERS SPACED APART AT DISTANCES PROPORTIONAL TO THE PRESSURES- 

 OF OXYGEN DISSOLVED IN SOLUTION. (A.t r Barcroft.) 



are plotted in the form of a curve (Fig. 137). There has to be 

 subtracted from the total volume of gas found the amount which is 

 calculated to be simply dissolved. The following table gives examples 

 of the results obtained for horse's blood at 38 C. : 



Oxygen ' C.C. catenated at 

 N. T. and P. t 100 C.C. of Blood. 



Oxygen Pressure. 



Chemically 

 bound. 



Dissolved in 

 Plasma. 



Degree of 



Saturation 



per Cent. 



Degree of 



Dissociation 



per Cent. 



It is found that above a tension of oxygen of 150 millimetres, corres- 

 ponding to an atmospheric pressure of 760 millimetres, the amount 



