OXYGEN. 419 



in accordance with the gas laws. The chemically bound oxygen, on the 

 other hand, is only affected materially by low pressures. 



We must not fail to mention that recently Ch. Bohr 1 has made certain 

 observations which tend to shatter the belief that the oxygen combination 

 by hemoglobin is a constant quantity. 2 Bohr speaks of a specific oxygen 

 capacity of the blood in different animals and different individuals. The 

 proportion of hemoglobin, or of the iron contained in it, to the amount of 

 oxygen consumed, varies. In order to explain this fact, Bohr makes the 

 assumption that the pigment in the blood is not a simple substance, but 

 is composed of different components, which separately combine with vary- 

 ing amounts of oxygen. It is conceivable that each individual blood 

 corpuscle originally incloses a uniform pigment, the specific nature of 

 which is gradually attained in various ways. This would account for 

 the fact that iron and oxygen are often found in unequal atomic propor- 

 tions. It must be emphasized, however, that Bohr's assumption is to be 

 regarded merely as an hypothesis. It is by no means satisfactorily proved. 

 We have mentioned these investigations of Bohr, partly because they open 

 up again to experimental research one of the few fields which had appar- 

 ently been investigated exhaustively. Once more our interest is aroused 

 concerning all the questions regarding the transportation of oxygen, 

 new inquiries are suggested, and a process which has been regarded as 

 simple, is perhaps to be looked upon as of quite complicated mechanism. 



In order to understand correctly the transportation of oxygen in the 

 blood, the process by which it is taken up in the lungs and given up to 

 the tissues, we must for the present stop attempting to trace the course 

 of the oxygen, but concern ourselves with one of the end-products which 

 results from the oxidation (combustion) of the organic substances in the 

 tissues; namely, carbon dioxide. This is necessary, because, according to 

 Bohr's investigations, it is evident that definite relations exist between the 

 oxygen content of the red corpuscles and the carbon dioxide content of 

 the blood. The carbon dioxide in the blood comes, as we have said, from 

 the tissues. It is formed everywhere in the cells as one of the end-products 

 in the metabolism of oxygen. There must, therefore, be developed in the 

 separate tissues a certain carbon dioxide gas pressure, which is in equilibrium 

 with the pressure exerted by this gas in the surrounding cell-complex, and 

 also with that in the blood. When the arterial blood, freshly laden with 

 oxygen, passes through these tissues, which are rich in carbon dioxide, 

 then gas will diffuse into the blood, for the pressure exerted by the carbon 

 dioxide in the blood is less than that of the tissues. The amount of carbon 

 dioxide in arterial blood has been found to average 40 per cent by volume, 

 but this varies greatly. In venous blood, i.e., that which is flowing away 



1 Handbuch der Physiol. loc. ciL p. 93. 



J G. Hiifner: Arch. Anat. Physiol. 1894, 130. 



