HEMOGLOBIN 



487 



observations to amount to 90 per cent, and in his more recent investi- 

 gations to 75 per cent. If Hiifner's results were correct, then blood 

 ought to be saturated to the extent of 90 per cent if the 2 -tension in 

 the alveolar air amounts to 30 mm. Hg, but under these conditions 

 animals exhibit distinct indications of want of oxygen. Loewy 1 

 explains the want of oxygen which manifests itself in heights of 

 4000-5000 m. as due to a too great dissociation of the oxyhsemo- 

 globin, and also points out that working with normal blood there 

 exist considerable 'individual' differences between the bloods of 

 different persons and dogs as regards oxygen capacities. The mean 

 dissociation-tension of oxyhsemoglobin in man is given in the above 

 Figure, in which Loewy has also included the results obtained by other 

 observers. From the curve of human blood Loewy calculates the 

 following values : 



Saturation. 



Partial pressure of oxygen equals 10 35 '77 



15 44-52 



20 53-36 



25 62-40 



30 67-29 



35 71-09 



40 74-51 



45 77-81 



50 81-11 



Or if the partial pressures of oxygen be expressed in percentages of 

 atmospheric pressure : 



Pressure of oxygen corresponding to 2 per cent of an atmosphere 



3 

 4 

 5 

 5-5 



Saturation of 

 oxyhsemoglobin, 

 43-19 

 55-73 

 65-75 

 71-20 

 73-72 

 75-90 

 80-73 



The specific oxygen capacity of blood is defined by Bohr 2 as that 

 amount of oxygen expressed in cubic centimetres at 0and 760 mm. pres- 

 sure which is bound by one gramme of iron of the blood at body tempera- 

 ture (37-38) under an oxygen tension of 150 mm. or one atmosphere. 

 The most recent determinations on the absorption of gases by the 

 blood made by Krogh, 3 and by Bohr, Hasselbalch, arid Krogh, 4 are 

 based on the specific oxygen capacity of blood. For the determina- 

 tion of the amount of iron present in the blood, the amount of iron 

 per 100 grammes of blood was estimated in Bohr's laboratory by 



1 A. Loewy, Arch. f. (Anat. u.} Physiol. 1904, p. 233. 



2 Chr. Bohr, Skand. Arch.f. Physiol. 3. 101 (1891). 

 * August Krogh, ibid. 16. 390 (1904). 



4 Chr. Bohr, K. Hasselbalch, and A. Krogh, ibid. p. 402. 



