490 CHEMISTRY OF THE PROTEIDS CHAP, 



ever the pressure of the oxygen is, as already pointed out, and this 

 older view of Bohr has been confirmed by his recent investiga- 

 tions. 1 



From a biological point of view the results obtained by Bohr are 

 of great interest, because " even a high C0 2 -tension of the blood in 

 the lungs will exert no measurable influence on the absorption of 

 oxygen by the blood on its passage through the lungs, as here the 

 oxygen tension is high ; but when the blood reaches the tissues, the 

 oxygen tension becomes reduced, while simultaneously the C0 2 -tension 

 is raised, and thereby the giving off of oxygen by the blood will be 

 greatly facilitated, and therefore the amount of oxygen present in the 

 blood will be made use of to a much greater extent than would other- 

 wise be the case. If we assume the oxygen tension of venous blood 

 to be 25 mm. Hg, then on the assumption that C0 2 exerted no 

 influence on the absorption of O 2 , there would pass into the plasma 

 only 24 per cent of the amount of O 2 present in the red corpuscles, 

 and only this amount would be available to the tissues. If, however,, 

 the CO 2 -tension rises simultaneously to 40 or to 80 mm. Hg, then 60 

 per cent, and in the latter case even 78 per cent of the oxygen, may 

 be given off by the corpuscles, without the tension falling beneath 

 25 mm. Hg." 



At present it is still impossible to make any definite statement a& 

 to how oxygen is united to the haemoglobin molecule, but it is 

 generally assumed that the power of absorbing oxygen is dependent 

 on the iron, or the iron-containing radical haematin (p. 508). Oxygen 

 is absorbed normally, only, if the haemoglobin be in solution, but 

 crystals of reduced hemoglobin are converted into those of oxy- 

 hoemoglobin according to Ewald 2 and Bohr and Torup ; 3 as, however, 

 these crystals were moist, the conversion must have only been possible 

 owing to the presence of the moisture. Kiihne 4 and Preyer 5 have 

 shown that oxyhaemoglobin is markedly acid, while reduced 

 haemoglobin is not, and methaemoglobin, which contains the oxygen 

 in much firmer union than does oxy haemoglobin, is, according to 

 Menzies 6 and Jaderholm, 7 even more strongly acid than is oxy- 

 haemoglobin. Passing oxygen through a haemoglobin solution makes 



1 Chr. Bohr, Zentralbl. f. Physiol. 17. 713 (1903-1904). 



2 Aug. Ewald, Zeitschr.f. Biologie, 22. 459 (1886). 



3 Chr. Bohr and S. Torup, Skandinav. Arch. f. Physiol. 3. 69 (1891). 



4 W. Kiihne, Virchoiv's Archiv, 34. 423 (1865). 



5 W. Preyer, Zentralbl. f. d. med. Wissenschaften, 1867, No. 18 ; and in Pfliiger? 

 Archiv, 1. 395 (1868). 



6 J. A. Menzies, Journ. of Physiol. 17. 402 (1895). 



7 Axel Jaderholm, Zeitschr.f. Biologic, 20. 419 (1884). 



