THE GASES OF THE BLOOD 251 



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. 



Fig. 119. Curve of Dissociation of Oxyhaemoglobin at 35 C. (after Hiifner's Re- 

 sults). Along the horizontal axis are plotted the partial pressures (numbers 

 below the curve) of oxygen in air, to which a solution of haemoglobin was exposed. 

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

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

 Thus, on exposure to an atmosphere in which oxygen existed to the extent 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 satu- 

 ration. 



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

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

 pressure only produced an additional absorption of I c.c., and above 

 this increasing the pressure had very little effect. 



We may suppose that at the ordinary temperature and pressure 

 some oxygen is continually escaping from the bonds by which it is tied 

 to the haemoglobin; but, on the whole, an equal number of free mole- 

 cules of oxygen, coming within the range of the haemoglobin molecules, 

 are entangled by them, and thus equilibrium is kept up. If now the 



