254 



A MANUAL OF PHYSIOLOGY 



added to blood, even in considerable amount, all the carbon 

 dioxide in it can be obtained by the pump. From serum a great 

 deal, but not the whole, of the carbon dioxide can be likewise 

 pumped out. The residue (from 10 to 18 per cent, of the whole) 

 is set free on the addition of an acid, e.g., phosphoric acid. 



The most satisfactory explanation is that in the serum there 

 exist substances which can act as weak acids in gradually driving 

 out the carbon dioxide, when its escape is rendered easier by 

 the vacuum. The quantity of these, however, is so small that a 



FIG. 



AT 35- 



(AFTER 



108. CURVE OF DISSOCIATION OF OXYH^MOGLOBIN 

 HCFNER'S RESULTS). 



Along the horizontal axis are plotted the partial pressures (numbers below the 

 curve) of oxygen in air, to which a solution of hemoglobin was exposed. The 

 corresponding percentages of oxygen are given above the curve. Along the 

 vertical axis is plotted the percentage saturation of the hemoglobin with oxygen. 

 Thus, on exposure to an atmosphere in which oxygen existed to the exent of 

 i per cent., corresponding to a partial pressure of 7'6 mm. of mercury, the haemo- 

 globin took up about 75 per cent, of the amount of oxygen required to saturate 

 it. When the oxygen was present in the atmosphere to the amount of about 10 per 

 cent., corresponding to a partial pressure of 76 mm. of mercury, the quantity 

 taken up by the haemoglobin was about 96 per cent, of that required for saturation. 



portion of the carbon dioxide remains in the serum. The proteins 

 of the serum, such as serum-globulin, behave in certain respects like 

 weak acids, and may contribute to the driving out of the carbon 

 dioxide. When defibrinated blood is pumped out, the whole of the 

 carbon dioxide can be removed, apparently because substances of 

 acid nature pass from the corpuscles into the serum and help to break 

 up the carbonates, and because the haemoglobin in the corpuscles 

 acts as a weak acid. 



In the red corpuscles a portion of the carbon dioxide is in 

 combination with alkalies. We know that the corpuscles contain 



