806 CHEMISTRY OF RESPIRATION. 



dissociation in vacuo, it must be assumed that the serum contains other 

 weak acids, in addition to the carbon dioxide, which contend with it for 

 the alkalies, and which expel the carbon dioxide from simple carbonates 

 in vacuo. The carbon dioxide which is expelled by means of the pump, 

 and which, without regard to the quantity merely absorbed, is generally 

 designated as " carbon dioxide in loose chemical combination," is thus 

 only obtained in part in dissociable loose combinations; in part it origi- 

 nates from the simple carbonates, from which it is expelled, in vacuo, by 

 other weak acids. 



These weak acids are thought to be in part phosphoric acid and in 

 part globulins. The importance of the alkali phosphates in the car- 

 bon dioxide combination has been shown by the investigations of FERNET ; 

 but the quantity of these salts in the serum is, at least in certain kinds 

 of blood, for example, in ox-serum, so small that it can hardly be of 

 importance. In regard to the globulins, SETSCHENOW is of the opinion 

 that they do not act as acids themselves, but form a combination with 

 carbon dioxide, producing carboglobulinic acid, which unites with the 

 alkali. According to SERTOLi, 1 whose views have found a supporter 

 in TORUP, the globulins themselves are the acids which are combined 

 with the alkali of the blood-serum. In both cases the globulins would 

 form, directly or indirectly, that chief constituent of the plasma or of 

 the blood-serum which, according to the law of mass action, contends 

 with the carbon dioxide for the alkalies. By a greater partial pressure 

 of the carbon dioxide the latter deprives the globulin alkali of a part of 

 its alkali, and bicarbonate is formed; by low partial pressure carbon 

 dioxide is set free and it is abstracted from the bicarbonate by the 

 globulin alkali. It must also be added that the above-mentioned car- 

 boglobulinic acid can perhaps be considered as a dissociable combination 

 of carbonic acid and protein. 



The assumption that the proteins of the blood are bodies active in 

 combining with the carbon dioxide has received some support from the 

 investigations of SIEGFRIED 2 on the combination of carbon dioxide with 

 amphoteric amino bodies. SIEGFRIED has found that amino-acids com- 

 bine with carbon dioxide, thereby being converted into carbamino- 



H 

 acids (glycocoll) for example, into carbamino acetic acid, CH 2 N COOII, 



COOH 



and that the carbon dioxide can be readily split off from these compounds. 

 The peptones and serum proteins in the presence of calcium hydroxide 



1 Hoppe-Seyler, Med. chem. Untersuch., 350. 



2 Zeitschr. f. physiol. Chem., 44 and 46. 



