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GAS EXCHANGE. OXYGEN TENSION. 859
Oxygen occurs in the blood in a disproportionately large part as
oxyhemoglobin, and the law of the dissociation of oxyhemoglobin is
of fundamental importance in the study of the tension of the oxygen
in the blood.
Attempts have been made to prove this law by investigations on
pure solutions of haemoglobin, and Hufner * has made very careful and
important determinations on such solutions. Recent investigations
of Bohr 2
and his pupils, as well as of Loewy and Zuntz,3
have shown
that the conditions in the blood are different from a pure hemoglobin
solution, which, in part, may be due to a change in the hemoglobin
brought about in its preparation. A hemoglobin solution in which
alcohol is used in preparing it, combines more firmly with oxygen than
the blood, and the dissociation tension of the oxygen is greater in blood
than in such a hemoglobin solution.
The oxygen tension may be variable, as Loewy 4
has shown, with
different individuals, and it is not the same in the blood of different
animals with the same oxygen pressure; for example, it is less in cat’s
blood than in the dog, horse and human blood. The temperature is also
of great importance, as the dissociation tension increases with a rise in
temperature, and with the same pressure the blood combines with less
oxygen at a high temperature than at a low temperature. The influence
of the concentration of the hemoglobin manifests itself in that in dilute
solutions the oxygen is more firmly combined (Hufner, Loewy and Zuntz,
Bohr) and that consequently blood made laky with water has a lower
dissociation tension and a firmer binding of the oxygen than undiluted
blood.
Of especial interest is the finding of Bohr, Hasselbalch and Krogh 5
that the CO2 present also influences the oxygen taken up, in that as the
carbon dioxide tension (also within physiological limits) increases the
oxygen taken up diminishes. The laws of oxygen absorption must
be determined by determinations upon blood itself, at the same time
observing the temperature and the carbon dioxide tension. A series of
determinations made by Krogh 6
upon horse’s blood at 38°, and a con-
stant carbon dioxide tension, is given below. In calculating the results
in column 4 the quantity of oxygen chemically combined at 150 mm.
oxygen pressure is equal to 100.
1
Arch. f. (Anat, u.) Physiol., 1890 and 1894.
2
See Nagel’s Handbuch, and Krogh, Skand. Arch. f. Physiol., 16.
»Arch. f. (Anat. u.) Physiol., 1904.
« Ibid.
6
Centralbl. f. Physiol., 17, and Skand. Arch. f. Physiol., 16.
6
Skand. Arch. f. Physiol., 16.
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