4 i6 TEXT-BOOK OF PHYSIOLOGY 



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 3.11 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 



O.O O.O IOO.OO O.OO 



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 oi 

 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, anc 

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

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



The limit of pressure at which the plasma ceases to absorb carbor 

 dioxid physically and begins to combine it chemically is not very clearly 

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

 only about 2.5 volumes are so absorbed, the remainder being in a conditior 

 of both loose and stable combination. 



An analysis of the serum, and presumably of the plasma, shows th< 

 presence of sodium salts, with which the carbon dioxid could enter into com 

 bination, viz.: sodium carbonate and dibasic sodium phosphate. Th< 

 sodium is thus partly divided between carbonic acid and phosphoric acid 

 The amount of the sodium which falls to carbon dioxid will depend on thi 

 mass influence of the latter; that is, its partial pressure. 



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

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

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

 bicarbonate, as shown in the following equation: 



2 + H 2 O=-2NaHCO 3 . 



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 

 with the formation of sodium bicarbonate and monobasic sodium phosphate 

 as shown in the following equation: 



Na 2 HP0 4 H-C0 2 +H 2 0=NaHC0 3 + NaH 2 P0 4 . 



In addition to the amount of CO 2 physically absorbed by the plasma an 

 chemically combined with sodium, a third portion is more or less loosel 

 combined with the protein constituent, globin, of the red corpuscle. A 

 this is the case the corpuscles must be regarded as carriers of CO 2 from th 

 tissues to the lungs as well as carriers of oxygen. It has also been suggeste 



