594 THE GASES OF THE BLOOD 



ence of carbonic acid, in the reverse carbonic acid combina- 

 tion proves to be relatively independent of the degree of 

 oxygen saturation of the hemoglobin. 35 From this it has 

 been concluded that carbonic acid enters into combination 

 with the globin component, not the hsematin, of the haemo- 

 globin. 



In the matter of the nature of the combination of car- 

 bonic acid with proteins, Siegfried's carbaminoreaction (v. 

 Vol. I of this series, pp. 86-88, Chemistry of the Tissues) 

 seems suited to furnish some suggestion. The statement 

 may be recalled that aminoacids >are capable of loosely fixing 

 carbonic acid in accordance with the equation : 



R-N/5 

 I \ H + 



I \ + C0 2 = I 

 COOH COOH 



Siegfried, basing his views upon observations upon poly- 

 peptids, believes that any place in the body where protein 

 and carbonic acid combine, the latter is fixed as above ; from 

 which standpoint the observations upon C0 2 fixation in the 

 blood, especially those of Sertoli, Setschenow, Bohr and 

 others, appear in a new light. 30 



Process of Exchcmge Between the Blood Corpuscles and 

 Serum. The proteid substances are contained in the blood 

 partly in alkaline combinations, and there can be no doubt 

 that when carbonic acid comes in contact with them a por- 

 tion of the alkali is withdrawn through the mass action of 

 the carbonic acid. The increase in the amount of diffusible 

 alkali in the blood serum which has. been noted by N. Zuntz 

 and A. Lb'wy and by L. Fredericq when carbonic acid is 

 introduced into the blood, finds an explanation from this 

 view, Zuntz assuming that alkaline carbonate passes in this 

 way from the blood cells into the plasma. Hamburger has, 

 however, observed that coincidently with this the chlorine 



88 A. Lowy, Handb. d. Biochem., 4', 56, 1908, ascribes some ability, even 

 though but small, to oxygen to displace carbonic acid from the blood. 



88 M. Siegfried (Leipzig), in collaboration with C. Neumann and H. 

 Liebermann, Zeitschr. f. physiol. Chem., 44, 85, 1905; 46, 401, 1905; 54, 423, 

 437, 1908. 



