TRANSPORT OF CARBON-DIOXIDE 333 



(proteins, water and crystalloid bases) about 26 c.c., and the 

 corpuscles about 19 c.c. 



As stated above, the free carbon-dioxide of the blood represents 

 only about 1/20 of the total carbon-dioxide carried. The forms in 

 which the combined carbon-dioxide of the blood is carried must 

 therefore be sought. 



Transport of COo in chemical combination with the blood constituents. 



It is assumed that the CO2 carried in the blood in chemical 

 combination is found there as bicarbonates, because the whole of 

 it may be removed if the blood is treated with an acid stronger 

 than H2CO3. This latter reaction is assumed to be of the nature 

 expressed by BHCO3 + HA =- BA + HgCOg, where B is a basic 

 radicle and HA is an acid. It is, however, found that the whole 

 of the COo of the blood may be removed by subjecting the blood to 

 a high vacuum. This is not the case for a simple bicarbonate 

 solution, which under a vacuum only gives off half its COo (2BHCO3 

 = B0CO3 + H2O + CO2). Plasma subjected to a vacuum reacts 

 like a pure solution of bicarbonate and gives off only half its COg. 

 The re-addition of erythrocytes to such plasma, which is again 

 subjected to a high vacuum, permits the removal of the remaining 

 CO2. There is, therefore, some substance in the red cells, which 

 acts as a weak, non-volatile acid in its relation to the carbon 

 dioxide of the blood, and can displace the latter from its combina- 

 tion as carbonates if each small amount of the latter is removed as 

 produced, owing to the low pressure at which the reaction is 

 carried out. It has been found that this substance is the haemoglobin 

 of the red blood corpuscle. 



BHCO3 + HA — BA + H2O + C02*(*volatile-removed as formed). 



(weak) 



Absorption curve of CO 2 in blood. 



A curve showing the volume of gas absorbed by blood under 

 different pressures of the gas can be drawn for carbon-dioxide as 

 for oxygen. The general shape of the curve is rather like that of 

 the absorption of oxygen by a solution of pure haemoglobin than 

 like the oxygen absorption curve of the blood, i.e. it is not sigmoid. 

 The volume of carbon-dioxide absorbed at a given tension is found to 

 depend on the degree of oxygenation of the haemoglobin. The higher 

 the saturation of the haemoglobin with oxygen, the less the CO2 

 absorption. (The converse influence of COg in O2 absorption has 

 already been noted.) 



The hydrogen ion concentration is also an important factor in 



