COMBINING POWER OF HEMOGLOBIN WITH OXYGEN 



The large quantity of oxygen found in arterial and in venous blood is the 

 more striking when the facts of absorption of gases by liquids are reviewed. 

 A liquid such as water will, when exposed to a gas, take up the gas by absorp- 

 tion according to definite physical laws. Under constant temperature the 

 amount of gas absorbed, oxygen for example, varies directly as the pressure 

 of the gas, or partial pressure if ,the gas is a mixture. The oxygen absorbed 

 by water from pure air as compared with expired air is in direct proportion 

 to the partial pressure of oxygen in the two airs, which is as 159 to 122. 



The amount of gas absorbed for a unit of fluid under standard tempera- 

 ture and pressure (one atmosphere at o C.), called its absorption coefficient, 

 is about the same for blood-plasma as for water. Before one can determine 

 the actual amount of oxygen in the plasma, the tension or absorption pressure 

 must be determined. 



The tension of the oxygen in arterial blood is found by an instrument 

 which enables one to measure the pressure at which oxygen is neither ab- 

 sorbed nor given off. The instrument commonly used is called an aerotonom- 

 eter. The principle of the instrument depends upon the fact that blood 

 exposed to mixtures of the gases in air tends to give up or absorb gases from 

 the air until complete equilibrium is established. 



By this means observers have measured the tensions of the blood gases. 

 The results have not been very constant, but the oxygen tension has been 

 found to be from 4 (Strassburg) 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. 



Blood-plasma exposed to an air with a partial pressure of 30.4 to 76 mm. 

 of mercury would absorb only from o.i to 0.3 (0.26 c.c. Pfliiger) of a cubic 

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

 blood contains from 20 to 22 c.c. of oxygen. It is evident that blood cannot 

 hold the oxygen in simple solution, but must retain it in chemical combina- 

 tion. The red blood-corpuscles have been shown to carry the excess of 

 oxygen by virtue of the special respiratory pigment, hemoglobin. 



Combining Power of Hemoglobin with Oxygen. One hundred 

 cubic centimeters of blood contain about 14 grams of hemoglobin, page 120. 

 Each gram of hemoglobin, when fully saturated with oxygen, according to 

 Hufner's earlier determination, combines with 1.56 c.c. of oxygen. By later 

 more careful work he gets the determination of 1.34 c.c. for hemoglobin of 

 ox blood. This last figure indicates that the combining power of the hemo- 

 globin is dependent upon the iron in the molecule, in which one atom of iron 

 combines with one atom of oxygen. The later investigation of the conditions 

 under which hemoglobin combines with oxygen are by Hiifner, on the one 

 hand, and Loewy, on the other. The former worked with purified solutions 

 of hemoglobin, the latter with blood. The average results of the investigations 



