RESPIRATORY CHANGES IN THE BLOOD 



305 



blood gases. The oxygen tension has been found to be from 4 (S trass- 

 burg) to 10 (Herter) per cent, of an atmosphere. Many determinations 

 have been given of both lower and higher percentages, but, accepting the 

 above limits for a working average, the oxygen tension in arterial blood 

 would be from 30.4 to 76 mm. of mercury or more. 



Blood plasma exposed to an air with a partial pressure of 30 to 76 mm. 

 of mercury would absorb only from o.io to 0.32 (0.26 c.c. Pfluger) c.c. 

 of oxygen for 100 c.c. of blood. As a matter of fact 100 c.c. of whole 



100 

 90 



80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



10 20 30 40 50 60 70 80 90 100 



FIG. 238. Dissociation curves of oxyhemoglobin. The figures along the ordinates 

 represent percentages of saturation of hemoglobin by oxygen. The figures along the 

 abscissae represent mm. of oxygen pressure in mercury. 



I. Bohr's dissociation curve of oxyhemoglobin dissolved in water. 



II. Dissociation curve of oxyhemoglobin dissolved in Ringer's Solution. (After 

 Barcroft and Camis.) 



blood has a capacity of an average of from 18.5 c.c. (the Haldane stand- 

 ard) to 22.6 c.c. or more of oxygen. It is evident that blood carries far 

 more oxygen than can be held in simple solution. The red blood corpus- 

 cles carry their enormous excess of oxygen by virtue of the special respira- 

 tory pigment, hemoglobin. 



