RESPIRATION 419 



with a view of determining in how far the discharge of the gases follows the 

 law of falling pressures. For convenience the conditions of each gas will 

 be considered separately. 



Oxygen. If blood is subjected to a succession of pressures progressively 

 less than the standard, it is found that though oxygen is evolved, its evolution 

 is not in accordance with the law of partial pressures; that is, in proportion 

 to the diminution of pressure. Within wide limits e.g., from 760 to 332 

 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, i.e., 70 mm. 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. Coin- 

 cidently 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, scarcely amounting to more than 0.36 c.c. per 100 c.c. 

 of blood. The agent therefore which holds the oxygen in combination is 

 the red corpuscle, 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 absorp- 

 tion the hemoglobin changes in color from bluish-red to scarlet-red and 

 changes from hemoglobin to oxyhemoglobin. The reverse method, that of 

 subjecting oxyhemoglobin 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 hemo- 

 globin combines with 1.4 c.c. of oxygen, and as the percentage of hemoglo- 

 bin is 13.50 to 14, it is evident that there is sufficient hemoglobin to com- 

 bine with practically all the oxygen usually present in the blood. Thus the 

 hemoglobin in 100 c.c. of blood would hold in combination 19.60 c.c. of 

 oxygen. This, together with the 0.3 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 0.3 per cent, is 

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

 ically 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 



