420 TEXT-BOOK OF PHYSIOLOGY 



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 Htifner shows 

 the relative proportion of hemoglobin and oxy hemoglobin in blood contain- 

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

 pressures: 



Atmospheric Pressure Partial Pressure of Oxygen Hemoglobin Oxyhemoglobin 



in mm. Hg. in mm. Hg. Percentage. Percentage. 



760 159.3 I -49 98.5 1 



524.8 no 2.14 97.86 



357.8 75 3-" 96-89 



238.5 50 4.60 95-40 



119.3 2 5 8.79 91.21 



47.7 10 19-36 80.64 



23-8 5 32.51 67.49 



0.0 0.0 100.00 0.00 



Carbon Dioxid. The blood yields up its contained carbon dioxid to the 

 vacuum of the gas-pump as completely as it does its oxygen. The same is 

 not the case, however, if the red corpuscles are first removed and the ex- 

 periment made with either plasma or serum. Even at zero pressure the fluid 

 contains carbon dioxid, as shown by its liberation on the addition of some 

 weak acid, as tartaric or phosphoric, an indication that it exists in a state of 

 firm combination. The same result follows the addition of the red blood- 

 corpuscles, which act in a manner similar to the acids just mentioned. 

 This property of the corpuscles has been attributed to hemoglobin, and 

 especially when in the state of oxyhemoglobin. It is for this reason that 

 blood yields all its carbon dioxid to the vacuum of the gas-pump. 



The results of chemic analysis indicate that the carbonic acid exists in 

 the blood under three conditions: (i) in solution; (2) in combination with 

 alkaline bases and (3) in combination with the protein constituents of the 

 red corpuscles and plasma. 



1. In solution. The percentage of carbonic acid held in solution by 

 the plasma is for physical reasons quite small. The limit of pressure at 

 which the plasma ceases physically to absorb carbon dioxid is not clearly 

 defined. It has been estimated that of the entire amount, 38 to 45 

 volumes, only about 2 volumes are so absorbed. 



2. In combination with alkaline bases. The percentage combined with 

 alkaline bases has been estimated at 18 per cent. An analysis of the 

 serum, and presumably of the plasma, shows the presence of sodium 

 salts, with which the carbon dioxid could enter into combination, viz. : 

 sodium carbonates and dibasic sodium phosphate. The sodium is thus 

 partly divided between carbonic acid and phosphoric acid. The amount 

 of the sodium which falls to carbon dioxid will depend on the mass in- 

 fluence of the latter; that is, its partial pressure. 



At its origin in the tissues the carbon dioxid acquires a considerable 

 tension, and its mass influence is correspondingly large. On entering the 

 blood it combines with sodium carbonate, with the formation of sodium 

 bicarbonate, as shown in the following equation: 



At the same time, having a greater mass influence than the phosphoric acid, 

 it will withdraw from the dibasic sodium phosphate one-half of its sodium, 



