OXYGEN. 



415 



ent partial pressures of this gas, show, within certain limits, but a slight 

 variation. The blood-plasma is able to take up only 0.65 per cent by 

 volume of oxygen. 1 As a matter of fact, the arterial blood contains more 

 than 70 times as much oxygen. Again, if blood be placed under an air- 

 pump, the oxygen is not removed from it at all in proportion to the 

 change in gas pressure. The oxygen does not leave the blood to any 

 extent until the pressure has been reduced to 358 millimeters Hg. 



Since the blood-plasma contains, as stated above, 0.65 per cent by 

 volume of absorbed oxygen, the rest of the oxygen contained in blood 

 must be held in some sort of chemical combination; and, obviously, this 

 union is effected with the blood corpuscles. In the arterial blood of a dog, 

 Pfluger 2 found, on an average, 22 per cent of oxygen by volume. If now a 

 solution of hemoglobin is employed, containing the same amount of hemo- 

 globin as the blood, it will be found that this solution, within narrow limits, 

 is capable of absorbing the same amount of oxygen as the blood. This 

 shows that it must be the hemoglobin which combines with the greater 

 part of the circulating oxygen in the blood. When hemoglobin 

 absorbs oxygen, it is changed into oxyhemoglobin; one molecule of 

 hemoglobin unites with one molecule of oxygen, or for one gram of hemo- 

 globin there are required 1.56 cubic centimeters of gas (measured at C. 

 and 760 millimeters pressure) . Dog's blood contains approximately 14.5 

 per cent of hemoglobin. From this it is evident that 22.6 per cent by 

 volume (1.56 X 14.5) of oxygen can be absorbed by the blood of a dog. 

 This agrees well with the amount found by actual experiment. It is, how- 

 ever, not permissible to apply the results obtained by working with hemo- 

 globin solutions directly to the absorption of oxygen by the blood under 

 different conditions. There are a number of facts known which show 

 that there are certain differences as regards the behavior of the two liquids. 

 This may be accounted for in different ways. It is conceivable that certain 

 changes may have taken place in the preparation of the hemoglobin solu- 

 tion. On the other hand, the possibility exists that the hemoglobin in the 

 blood is influenced by the way it is contained in the blood corpuscles. It is, 



1 Christian Bohr, Skand. Arch. Physiol. 17, 104 (1905), has recently computed the 

 absorption coefficients of the plasma and blood for different gases: 



a E Pfluger: Zentrb. med. Wiss. 1867, 722, and Pfliiger's Arch. 1, 274, 288 (1868). 



