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854 RESPIRATION AND OXIDATION.
addition of an acid. The red blood-corpuscles also act as an acid, and
therefore in blood all the carbon dioxide is expelled in vacuo. Hence
a part of the carbon dioxide is in firm chemical combination in the serum.
Absorption experiments with blood-serum have shown us further that
the carbon dioxide which can be pumped out is in greater part loosely
chemically combined, and from this loose combination of the carbon
dioxide it necessarily follows that the serum must also contain simply
absorbed carbon dioxide. For the form of binding of the carbon dioxide
contained in the serum or the plasma, there are the three following pos-
sibilities: 1. A part of the carbon dioxide is simply absorbed; 2. Another
part is in loose chemical combination; 3. A third part is in firm chemical
combination.
The quantity of physically dissolved carbon dioxide in the serum
cannot be higher than about 2 vols, per cent, as the quantity of carbon
dioxide in the plasma corresponding to 100 cc. of blood is given above
as 1.42 cc.
The quantity of carbon dioxide in the blood-serum which is combined
as a firm chemical union depends upon the quantity of simple alkali
carbonate in the serum. This amount is not known, and it cannot be
determined either by the alkalinity found by titration, nor can it be cal-
culated from the excess of alkali found in the ash, because the alkali is not
only combined with carbon dioxide, but also with other bodies, especially
with protein. The quantity of carbon dioxide in firm chemical combi-
nation cannot be ascertained after pumping out in vacuo without the
addition of acid, because to all appearances certain active constituents
of the serum, acting like acids, expel carbon dioxide from the simple
carbonate. The quantity of carbon dioxide not expelled from dog-
serum by vacuum alone without the addition of acid amounts to 4.9
to 9.3 vols, per cent, according to the determinations of Pfluger.1
From the occurrence of simple alkali carbonates in the blood-serum
it naturally follows that a part of the loosely combined carbon dioxide
of the serum which can be pumped out must exist as bicarbonate. The
occurrence of this combination in the blood-serum has also been directly
shown. In experiments with the pump, as well as in absorption experi-
ments, the serum behaves in other ways differently from a solution of bicar-
bonate, or carbonate of a corresponding concentration; and the action
of the loosely combined carbon dioxide in the serum can be explained
only by the occurrence of bicarbonate in the serum. By means of a
vacuum, the serum always allows much more than one-half of the carbon
dioxide to be expelled and it follows from this that in the pumping out
1
E. Pflvip;er’s Ueber die Kohlensiiure des Blutes, Bonn, 1864, 11. Cited from
Zuntz in Hermann’s Handbuch, 65.
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