4 o6 TEXT-BOOK OF PHYSIOLOGY. 



mm. atmospheric pressure, to which correspond oxygen pressures of 159 

 and 70 mm. respectively there is but a slight increase in the amount of 

 oxygen evolved; and it is not until the pressure of the oxygen falls below 

 the latter that it begins to be liberated in large amounts. From this on, the 

 oxygen continues to be liberated with decreasing pressures, until the zero point 

 is reached, when all gaseous discharge ceases. Coincidently the blood 

 changes in color from a bright red to a deep bluish-red. It is evident from 

 the results of this procedure that the condition of the oxygen in the blood 

 is but to a slight extent one of physical absorption. The indications are 

 that the union is of the nature of a chemic combination. 



If the red corpuscles are removed from the blood and the plasma alone 

 treated in the manner above described, it will be found that the oxygen 

 liberated now follows the law of partial pressure. The amount so liberated, 

 however, is small about one per cent, of the total oxygen of the blood. 

 The agent therefore which holds the oxygen in combination is the red corpus- 

 cle, or more exactly, the hemoglobin, which constitutes about 32 per 

 cent, of its volume. This is proved by the fact that a solution of gas-free 

 hemoglobin of a strength equivalent to that of the blood (14 per cent.), 

 exposed to oxygen under a gradually increasing pressure from zero up to 50 to 

 70 mm. pressure, will absorb large quantities of oxygen; beyond this point the 

 amount absorbed is again small in comparison. At 70 mm. pressure the 

 hemoglobin is almost saturated. Coincidently with this absorption the hemo- 

 globin changes in color from bluish-red to scarlet-red and changes from hemo- 

 globin to oxyhemoglobin. The reverse method, that of subjecting oxy- 

 hemoglobin to gradually diminishing pressures, yields opposite results, that 

 is, the oxygen becomes dissociated and the force by which this is accomplished 

 is known as the force of dissociation. As one gram of hemoglobin com- 

 bines with 1.34 c.c. of oxygen, and as the percentage of hemoglobin is 13.50 

 to 14, it is evident that there is sufficient hemoglobin to combine with 

 practically all the oxygen usually present in the blood. Thus the hemoglobin 

 in looc.c. of blood would hold in combination 18.76 c.c. of oxygen. This, 

 together with the one c.c. held in solution in plasma, would equal the volume 

 obtained in the vacuum of the air-pump. 



The union of the oxygen with the hemoglobin is therefore largely chemic 

 in character, dependent however on pressure. About one per cent, is 

 physically absorbed by or dissolved in the plasma; the remainder is chemi- 

 cally combined with the hemoglobin. 



The association or combination of oxygen is favored by a pressure of at 

 least 30 to 50 mm. Hg. and upward; the dissociation, by diminution of 

 pressure. In the conversion of hemoglobin into oxyhemoglobin two an- 

 tagonistic forces are at work, heat and chemic affinity. The former 

 tends to prevent, the latter to favor, the union. Chemic affinity increases 

 with the influence of mass, that is, in proportion to the number of atoms in a 

 unit of volume, with the density, and with the partial pressure of the oxygen. 

 Diminution of pressure reduces the mass influence and permits the heat to 

 bring about dissociation (Bunge). The following table by Hiifner shows 

 the relative proportion of hemoglobin and oxyhemoglobin in blood contain- 

 ing 14 per cent, hemoglobin and exposed to air at gradually diminishing 

 pressures: 



