GASES BETWEEN BLOOD AND TISSUES. 783 
solutions of fresh blood, and determined the reduction of the oxy- 
hemoglobin by means of the spectroscope. The results show that the 
heart during contraction reduces the solution about ten times as quickly 
as when it is at rest. 
The causes of the exchange of gases between the blood and the 
tissues. — The cause of the passage of oxygen from the blood to the 
tissues, and of carbon dioxide from the tissues to the blood, appears to 
be the difference in the tension of these gases in the tissues, and in the 
lymph and blood which surround them. It has been shown that the 
tissues have a great affinity for oxygen, and even store it up for the 
future oxidation of some of their constituents ; and, on the other hand, 
that they are constantly producing carbon dioxide, and can even do this 
for a time in the absence of free oxygen. 
The above conclusion is supported by the analyses of the gases of 
lymph and other secretions, and the determinations of the tensions of 
the gases in those fluids. Hammarsten 1 found that the lymph of a dog 
contained 0*1 volume per cent, of oxygen, 37"5 of carbon dioxide, and 
1*6 of nitrogen. These results have been confirmed and extended by 
other observers. 2 Oxygen is present only in traces, but the quantity of 
carbon dioxide is less than that found in venous blood. This latter fact 
does not prevent the passage of carbon dioxide from the lymph to the 
venous blood, for Gaule 3 has shown that the tension of the gas is higher 
in the former fluid. It must be admitted, however, that further experi- 
ments are needed upon this point, for Gaule's experiments are not con- 
clusive, and Strassburg found the tension of carbon dioxide in lymph 
to be intermediate between that in arterial and venous blood. Another 
probable cause of the smaller quantity of carbon dioxide in lymph is 
that many of the analyses were made upon lymph from the thoracic 
duct ; the lymph would have been exposed in that situation to the 
action of arterial blood. This difficulty, however, is not present in some 
of the secretions. Thus, Strassburg i found in the urine and bile of a 
dog a tension of carbon dioxide equal to 9 — 7 per cent, of an atmo- 
sphere. Further, this physiologist has shown that, if air is injected into 
a ligatured portion of the intestine of a living dog, and after a short 
time is analysed, the tension of carbon dioxide is 7 '7 per cent, of an 
atmosphere ; that is, considerably greater than the tension of the gas in 
the venous blood. 
These results are confirmed by the analyses 5 of some of the 
secretions of the body, and of various pathological transudations (see 
tables on p. 784). 
Ewald also determined the tension of carbon dioxide in some of these 
fluids, and found results as' high as 7'51, 1092, 10*73, and 11*5 per cent, 
of an atmosphere. It is therefore permissible to conclude that the tension 
of carbon dioxide in the tissues which produce, and are in contact with, 
these fluids is higher than the tension of that gas in the venous blood. 
1 Ber. d. k. sacks. Gesettsch. d. Wissensch. Math.-phys. CI., Leipzig, 1871, Brl. \xiii 
S. 617. 
2 Daehnhardt and Hensen, Virckows Archiv, Bd. xxxvii. S. 55, 68; Tsehiriew, Ber. 
d. k. sacks. Gesellsch. d. Wissensch. Math.-phys. 01., Leipzig, 1874, Bd. xxvi. S. 120; 
Buchner, Arb. a. d. physiol. Anst. zu Leipzig, 1876, Bd. xi. S. 10S. 
3 Arch./. Physiol., Leipzig, 1878, S. 469. 
4 Arch./, d. ges. Physio/., Bonn, 1872, Bd. vi. S. 94. 
5 Tables given by Halliburton, "Text-Book of Chemical Physiology and Pathology," 
London, 1891, p. 392. 
