OXYGEN. 423 



could not be removed by the air-pump. Pfliiger proved this amount of 

 carbonic acid to be present by adding acid to the plasma. In other words, 

 Pfliiger assisted the action of the protein, which was insufficient to take 

 the place of all the carbonic acids in the blood, by the artificial addition of 

 a stronger acid, which expelled the remainder of the carbonic acid that was 

 combined with the alkali. 



From these experimental results, we can describe the combination of 

 the carbonic acid in the plasma, somewhat as follows: A part of the 

 carbon dioxide is evidently present, even with low pressures of gas, as 

 bicarbonate. With increasing carbon dioxide pressures, a part of the gas 

 replaces the protein in its combinations with the alkali. In this way we 

 are able to understand much better how the carbon dioxide gas exchange 

 takes place, although it cannot yet be said that the entire process has been 

 satisfactorily explained. 



The reason that we do not at present understand clearly the exact way 

 in which the carbon dioxide is combined in the plasma, and have no exact 

 data concerning the dissociation of the separate compounds, is because 

 the plasma itself is a complicated mixture of unlike substances, which 

 mutually influence one another in a number of different ways. The study 

 of the behavior of the bicarbonates alone, or, on the other hand, of the 

 albuminates, does not lead to results which can be applied directly to 

 the plasma, for it is at present impossible for us to imitate precisely 

 the conditions prevailing in this fluid. 



There is no doubt that alkali phosphates which are always present in 

 the plasma, even although in small amounts, also have an effect upon 

 the combination with carbonic acid. When exposed to the action of car- 

 bon dioxide, Na 2 HPO 4 is attacked with the formation of NaH 2 PO4 and 

 NaHCO 3 . 



According to the results obtained by Setschenow, 1 the removal of the 

 alkali from alkali albuminates takes place only with carbon dioxide pressures 

 which are greater than those ordinarily prevailing in the living organism. 

 Thus we may have in these compounds a regulating mechanism which 

 prevents the carbon dioxide pressures from exceeding a certain maximum. 

 If the pressure of the gas exceeds this normal value, the alkali albuminates 

 then serve to unite with the excess of the carbonic acid, and thus prevent 

 any considerable pressure being exerted by the gas. 



Carbonic acid is likewise contained in the blood corpuscles, partly free, 

 and partly in a state of chemical combination. At 38 C., and 30 milli- 

 meters gas pressure, there is present in the blood corpuscles corresponding 

 to 100 cubic centimeters of blood, about 0.6 cubic centimeter of the gas, 

 which is simply physically dissolved. The greater part of the carbon 

 dioxide absorbed by the red corpuscles does not follow the laws for gas 



1 Memoires de TAcad. de St. Petersburg, 26, 60 (1879). 



