252 



RESPIRATION 



atmospheric pressure, and therefore the partial pressure of oxygen, is 

 reduced, the tendency of the oxygen to break off from the haemoglobin 

 will be unchanged, and as many molecules on the whole will escape as 

 before ; but even after a considerable reduction of pressure the haemo- 

 globin, such is its avidity for oxygen, will still be able to seize as much 

 oxygen as it loses. The more, however, the partial pressure of the 

 oxygen is diminished that is to say, the fewer oxygen molecules there 

 are in a given space above the haemoglobin the smaller will be the 

 chance of the loss being made up by accidental captures. At a certain 

 pressure the escapes will become conspicuously more numerous than 

 the captures; and the gas-pump will give evidence of this. The higher 

 the temperature of the haemoglobin is, the greater will be the average 

 velocity of the molecules, and the greater the chance of escape of mole- 

 cules of oxygen. 



It is easily proved that the substance in the corpuscles which 

 unites with oxygen is the blood-pigment. Although a solution of 



100 

 90 

 80 



is cxc. 



I6CXL 

 I4C.C 



12 ca 



IOC& 



see. 



6C.C. 

 4C.C. 



2 C.C. 

 03CC. 



10 20 JO 40 $0 60 70 60 90 100 110 120 130 140 ISO 



Fig. 120. Curves of Dissociation of Oxygen for Horse's Blood (B) and Dog's Hemo- 

 globin solution (H) at 38 C. (Bohr). The figures along the base-line are the 

 partial pressures of oxygen to which the blood and haemoglobin solution were 

 exposed. Those along the vertical axis on the left are the percentage saturations 

 with oxygen. The figures along the vertical at the right give the actual number 

 of c.c. of oxygen chemically combined by 100 c.c. of the blood for each pressure 

 of oxygen. The interrupted line P indicates the amount of oxygen dissolved in 

 the plasma of the blood at each partial pressure on the assumption that the 

 plasma is two-thirds of the volume of the blood. Thus, at 150 mm. oxygen 

 pressure the plasma of 100 c.c. of blood took up o - 3 c.c. oxygen. 



oxyhaemoglobin crystals behaves towards oxygen somewhat differ- 

 ently from blood containing the same proportion of the native pig- 

 ment, the maximum amount of oxygen taken up is the same for 

 each. The differences in the results of the various investigators 

 who have worked out the curves of dissociation for hemoglobin and 

 for blood (Figs. 119, 120, 121) are paitly explained by the fact that, 

 as is the case with similar dissociable compounds, the dissociation 

 tension varies with the temperature and the concentration of the 

 pigment. Another factor which was overlooked in the earlier 



