POWER OF HEMOGLOBIN WITH OXYGEN 



307 



higher pressures. Or, which amounts to the same, if hemoglobin saturated 

 with oxygen be subjected to decreasing oxygen pressure, it sets free the 

 combined oxygen, at first slowly, then more rapidly. By consulting the 

 typical curve showing this relation, it will be evident that the critical 

 partial oxygen pressures influencing this combination fall at about 30 to 

 35 mm. mercury of oxygen tension and below. See figure 238. 



A number of factors influence the dissociation of oxygen from hemo- 

 globin at a given oxygen tension. Of prime importance is the influence of 

 the presence of carbon dioxide gas as shown by Bohr and confirmed by 

 Barcroft and Camis. With an increase in the tension of carbon dioxide 

 there is a decrease in the fixation of oxygen. 



TABLE SHOWING THE DISSOCIATION OF OXHEMOGLOBIN IN THE PRESENCE OF VARY- 

 ING TENSIONS OF CARBON DIOXIDE. (BARCROFT AND CAMIS.) 



The salts of the blood also influence the oxygen fixation by hemo- 

 globin under a given tension as indicated in the following table: 



TABLE SHOWING THE INFLUENCE OF THE PRESENCE OF DIFFERENT SALTS ON 



THE PERCENTAGE OF SATURATION OF HEMOGLOBIN UNDER A 



CONSTANT OXYGEN TENSION OF 30 MM. MERCURY. 



(BARCROFT AND CAMIS.) 



1. Hemoglobin in water dissociation . : 62 per cent. 



2. Hemoglobin in o . 7 per cent. NaCl dissociation .... 75 per cent. 



3. Hemoglobin in Ringer's solution dissociation 85 per cent. 



4. Hemoglobin in NaHCO 3 solution dissociation 89 per cent. 



5. Hemoglobin in 0.9 per cent. KC1 dissociation 91 per cent. 



6. Hemoglobin in Na 2 HPO 4 solution dissociation. ... 93 per cent. 



Barcroft and Camis find that the dissociation curve also varies in the 

 blood of different animals. Strassburg gives the oxygen tension of arterial 

 blood as 29.64 mm. of mercury, and for venous blood 22.04 mm. of mer- 

 cury. That is to say, during the brief interval in which the blood is in 

 the pulmonary capillaries the oxygen tension has increased by 7.6 mm. 

 of mercury, an increase of tension which would produce very little increase 

 in simple absorption of oxygen. Yet it is sufficient to cause fixation of 

 from four to five volumes per cent, of oxygen by the hemoglobin. 



It is evident that there will be diffusion of oxygen from the high tension 



