RESPIRATION 



71 



40 mm. of CO2, as in average human alveolar air, was worked out 

 by Barcroft, and his results for one individual (Douglas) were 



2 3 4 >5 6 



PRESiORE OF OXYOEN 



7 S O 10 II 12 13 



IN PERCENTAGE OF ONE ATMOSPHERE . 



Figure 20. 



Dissociation curves of oxyhaemoglobin in presence of 40 mm. pressure of 

 CO2 at 38° (i per cent of an atmosphere = 7.60 mm. pressure). 



O Blood of C. G. D., using ammonia in blood-gas apparatus. 



• Blood of C. G. D., using Na2C03 in blood-gas apparatus. 



n Blood of J. S. H., using ammonia in blood-gas apparatus. 



■ Blood of J. S. H., using Na2C03 in blood-gas apparatus. 



X Mixed blood of six mice, using ammonia in blood-gas apparatus. 



approximately confirmed by Douglas and myself, working with 

 a different apparatus. Figure 20 shows the curves given by the 

 blood of Douglas and myself in a very exact series of observa- 

 tions, with the individual observations marked. Our curves as will 

 be seen are sensibly the same; but Barcroft has found that the 

 curves of different individuals may vary very distinctly. With the 

 blood of Douglas and myself, for instance, half-saturation of 

 the haemoglobin with oxygen occurs at an oxygen pressure of 4.0 

 per cent of an atmosphere or 30.4 mm. With that of other individ- 

 uals, and the same pressure (40 mm.) of CO2, half-saturation 

 may, according to Barcroft, occur at as low an oxygen pressure as 

 24 mm.22 



Barcroft, The Respiratory Function of the Blood, p. 218, 1913. 



