GAS EXCHANGE. OXYGEN TENSION. 859 



Oxygen occurs in the blood in a disproportionately large part as 

 oxy haemoglobin, and the law of the dissociation of oxy hemoglobin is 

 of fundamental importance in the study of the tension of the oxygen 

 in the blood. 



Attempts have been made to prove this law by investigations on 

 pure solutions of haemoglobin, and HUFNER l has made very careful and 

 important determinations on such solutions. Recent investigations 

 of BOHR 2 and his pupils, as well as of LOEWY and ZuNTZ, 3 have shown 

 that the conditions in the blood are different from a pure haemoglobin 

 solution, which, in part, may be due to a change in the haemoglobin 

 brought about in its preparation. A haemoglobin solution in which 

 alcohol is used in preparing it, combines more firmly with oxygen than 

 the blood, and the dissociation tension of the oxygen is greater in blood 

 than in such a haemoglobin solution. 



The oxygen tension may be variable, as LOEWY 4 has shown, with 

 different individuals, and it is not the same in the blood of different 

 animals with the same oxygen pressure; for example, it is less in cat's 

 blood than in the dog, horse and human blood. The temperature is also 

 of great importance, as the dissociation tension increases with a rise in 

 temperature, and with the same pressure the blood combines with less 

 oxygen at a high temperature than at a low temperature. The influence 

 of the concentration of the haemoglobin manifests itself in that in dilute 

 solutions the oxygen is more firmly combined (H.UFNER, LOEWY and ZUNTZ, 

 BOHR) and that consequently blood made laky with water has a lower 

 dissociation tension and a firmer binding of the oxygen than undiluted 

 blood. 



Of especial interest is the finding of BOHR, HASSELBALCH and KROGH 5 

 that the C02 present also influences the oxygen taken up, in that as the 

 carbon dioxide tension (also within physiological limits) increases the 

 oxygen taken up diminishes. The laws of oxygen absorption must 

 be determined by determinations upon blood itself, at the same time 

 observing the temperature and the carbon dioxide tension. A series of 

 determinations made by KROGH 6 upon horse's blood at 38, and a con- 

 stant carbon dioxide tension, is given below. In calculating the results 

 in column 4 the quantity of oxygen chemically combined at 150 mm. 

 oxygen pressure is equal to 100. 



1 Arch. f. (Anat. u.) Physiol., 1890 and 1894. 



2 See Nagel's Handbuch, and Krogh, Skand. Arch. f. Physiol., 16. 



3 Arch. f. (Anat. u.) Physiol., 1904. 



4 Ibid. 



5 Centralbl. f. Physiol., 17, and Skand. Arch. f. Physiol., 16. 

 e Skand. Arch, f . Physiol., 16. 



