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868 RESPIRATION AND OXIDATION.
of the plasma is of importance in the giving up of oxygen to the tissues,
as the blood corpuscles contain a supply of oxygen only sufficient to
replace that removed from the plasma by the tissue. This quantity
of oxygen, which is dissolved in the plasma and at the disposal of the
tissues, is dependent upon the oxygen tension in the blood and only
indirectly dependent upon the total quantity of oxygen in the blood.
As this tissue is almost or entirely free from oxygen, a considerable dif-
ference in regard to the oxygen pressure must exist between the blood
and the tissues. The possibility that this difference in pressure is suf-
ficient to supply the tissues with the necessary quantity of oxygen is
hardly to be doubted.
The animal body, it seems, also has the command over means of regu-
lating and varying the oxygen tension, and such a means is the carbon
dioxide produced in the tissue which, according to Bohr, Hasselbalch,
and Krogh,1
raises the oxygen tension. This is of special importance
when the tension of the oxygen in the blood of the capillaries is very low;
then the ability of the carbon dioxide to raise the dissociation tension
of the ox3’hsemoglobin comes into play, especially with low oxygen tension."
Another regulating moment is, Bohr claims, the specific oxygen capacity
of the blood, which means the relation of the maximum oxygen combina-
tion to the quantity of iron of the blood or the haemoglobin solution.
In regard to the carbon-dioxide tension in the tissue it must be
assumed a priori that it is higher than in the blood. This is found to
be true. Strassburg 2
found in the urine of dogs and in the bile a car-
bon-dioxide tension of 9 per cent and 7 per cent of an atmosphere,
respectively. The same experimenter has, further, injected atmospheric
air into a ligatured portion of the intestine of a living dog and analyzed
the air taken out after some time. He found a carbon-dioxide tension
of 7.7 per cent of an atmosphere. The carbon-dioxide tension in the
tissues is considerably greater than in the venous blood, and there is
no opposition to the view that the carbon dioxide simply diffuses from
the tissues into the blood according to the law of diffusion.
Several methods have been suggested for the study of the quantitative
relation of the respiratory exchange of gas. The reader must be referred
to other text-books for details as to these methods, and we will here
mention only the chief features of the most important methods. It must
also be remarked, in regard to these methods, that those of Regnault
and Reiset and of Pettenkofer, determine the total gas exchange,
and indeed for a long time, while the other three methods determine the
respiratory gas exchange alone, and this only for a short time.
1
Centralbl. f. Physiol., 17, and Skand. Arch. f. Physiol., 16.
2
Pfiuger’s Arch., 6.
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