OXYGEN. 



431 



several cases the tension of the carbon dioxide in the blood was less than 

 that of the air at the bifurcation. The following table gives an idea of 

 the results obtained : l 



These results indicate that neither the passage of oxygen from the alveo- 

 lar air to the blood, nor of the carbon dioxide from the blood to the alveolar 

 air, can be accounted for by diffusion alone. Some forces must be at 

 work which tend to make the oxygen more active towards its absorption 

 by the blood than can be accounted for by the partial pressures of the 

 oxygen gas, and at the same time these forces enable the blood to give up 

 its carbon dioxide even when the pressure of this gas is greater in the 

 alveoli than it is in the blood itself. Bohr compares the lung with a gland, 

 and conceives of its activity as that of a secretion. He assumes that 

 the lung-cells have the power of temporarily uniting with oxygen and with 

 carbonic acid. In fact, P. Ehrlich 2 has proved that the lungs possess an 

 extraordinarily strong reducing power. He injected alizarin-blue into 

 animals, this being a dyestuff which becomes colorless on reduction. The 

 lungs of an animal freshly-killed were then found to be colorless, the blue 

 color being apparent only after exposure to the air for some time. Now 

 the lung tissue, like all other tissue, has its own metabolism. It con- 

 sumes oxygen and evolves carbon dioxide. Its reduction power, according 

 to Ehrlich's results, however, is so pronounced that it seems perfectly 

 plausible to speak of an oxygen-secretion in the sense meant by Bohr. 



Bohr and Henriques 3 also made the discovery, which is of itself very 

 remarkable, that the lungs take an uncommonly large part in the general 



1 Cf. Bohr: Handbuch der Physiol. p. 146. Bohr measured directly the oxygen ten- 

 sion at the lung surface and compared this with the oxygen tension of the arterial blood. 

 There was in this case a more considerable excess of pressure in favor of the blood. 

 Cf. L. Fr&Iericq: Zentr. Physiol. 7, 33 (1893); 8, 34 (1897). Haldane and J. Lorrain 

 Smith: J. Physiol. 20, 497 (1896); and 22, 231 (1899). 



3 Sauerstoffbediirfnis des Organismus, Berlin, 1885. 



3 Oversigt. kgl. Danske Videnskabs-Selskabs forhandl. No. 1, 1897, Arch, physiol. 

 9, 590 and 710 (1897). 



