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CARBON DIOXIDE IN THE BLOOD. 855
not only may a dissociation of the bicarbonate take place, but also a
conversion of the double sodium carbonate into a simple salt. As we
know of no other carbon-dioxide combination, besides the bicarbonate,
in the serum, from which the carbon dioxide can be set free by simple
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-
1
Hoppe-Seyler, Med. chem. Untersuch., 350.
2
Zeitschr. f. physiol. Chem., 44 and 46.
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