GASES BETWEEN BLOOD AND TISSUES. 783 



solutions of fresh blood, and determined the reduction of the oxy- 

 hsemoglobin 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 l found that the lymph of a dog 

 contained O'l volume per cent, of oxygen, 3 7 '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 4 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, 10 - 92, 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 JBer. d. k. sticks. Gesellsch. d. Wissensdi. Math.-pkys. 01., Leipzig, 1871, Bd. xxiii. 

 S. 617. 



2 Daehnhardt and Hensen, Virchow's Archiv, Bd. xxxvii. S. 55, 68 ; Tschiriew, Ber. 

 d. Tc. sacks. Gesellsck. d. Wissensck. Math.-pJiys. 01. , Leipzig, 1874, Bd. xxvi. S. 120; 

 Buchner, Arb. a. d. pkysiol. Anst. zu Leipzig, 1876, Bd. xi. S. 108. 



3 Arch. f. PhysioL, Leipzig, 1878, S. 469. 



4 Arck.f. d. ges. PhysioL, Bonn, 1872, Bd. vi. S. 94. 



5 Tables given by Halliburton, "Text-Book of Chemical Physiology and Pathology," 

 London, 1891, p. 392. 



