25 2 RESPIRATION 



it is drawn, it yields more carbon dioxide and less oxygen than if it 

 is evacuated at once (Pfliiger). From this it is concluded that 

 oxidation goes on in the blood for some time after it is shed. The 

 oxidizable substances are, however, confined to the corpuscles, 

 which suggests that ordinary metabolism simply continues for 

 some time in the formed elements of the shed blood, and that the 

 disappearance of oxygen is not due to the oxidation of substances 

 which have reached the blood from the tissues. It is an interesting 

 fact that the rate of oxygen consumption of nucleated (bird's) erv- 

 throcytes is much greater than that of non-nucleated mammalian 

 corpuscles. The young non-nucleated erythrocytes, which in experi- 

 mental anaemia in mammals (e.g., after haemorrhage) find their way 

 in large numbers into the circulation, have a relatively intense 

 metabolism, and therefore consume a relatively large amount of 

 oxygen. 



The Distribution and Condition of the Oxygen in the Blood. The 

 oxygen is nearly all contained in the corpuscles. A little oxygen 

 can be pumped out of serum (0-2 or 0-3 per cent, by volume), but this 

 follows the Henry-Dalton law of pressures that is, it comes off in 

 proportion to the reduction of the partial pressure of the oxygen in 

 the pump, and is simply in solution. 



When blood at body temperature is shaken up with air at the 

 ordinary pressure, corresponding to a partial pressure of oxygen 

 of a little over one-fifth of an atmosphere (in round numbers 160 mm. 

 of mercury), the blood-pigment becomes saturated with oxygen or 

 nearly so. When the blood is now pumped out, very little oxygen 

 comes off till the pressure has been reduced to about half an atmo- 

 sphere, corresponding to a pressure of oxygen of about 80 mm. 

 At about 70 mm. partial pressure the dissociation is somewhat 

 greater. At a third to a quarter of an atmosphere (50 to 40 mm.; 

 the amount of oxygen liberated is markedly increased, and the dis 

 sociation becomes more and more rapid as the pressure falls to- 

 wards zero. This behaviour shows that the oxygen is not simply 

 absorbed, but is united, as a dissociable compound, to some con- 

 stituent of the blood. The same thing is, of course, seen when 

 defibrinated blood is saturated at body temperature with oxygen at 

 different pressures. As the partial pressure of the gas is increased 

 from zero the first increments of pressure correspond to a much 

 greater absorption of oxygen than further equal increments. Thus 

 as is seen in Fig. 120, with an oxygen pressure of 10 mm. 100 c.c. 

 of blood took up 6 c.c. of oxygen, or 30 per cent, of the amount 

 required to saturate it. When the pressure of oxygen was 30 mm. 

 over 16 c.c. of oxygen was absorbed, the blood being 80 per cent, 

 saturated. A further increase of the oxygen pressure to 40 mm. 

 increased the quantity of the gas taken up by only 2 c.c. (to 90 per 

 cent, saturation). Ttu next increment of 10 mm. in the oxygen 



