582 THE COLORING MATTER OF BLOOD 



extensive work of his pupil, Butterfield, 9 emphasize the view 

 that in iron proportions, ability to combine oxygen, and in 

 spectrophotometry of pure, unchanged red blood coloring 

 matter in all the instances of normal and diseased human 

 beings and animals examined, there is no variation. Of 

 course it has not been proved and (according to everything 

 immunology and precipitin study indicate) is not even prob- 

 able that the colorless protein components of all haemo- 

 globins of the general animal kingdom are actually identical 

 among themselves. The molecular weight of haemoglobin 

 has been estimated by Hiifner as about 16,000 (from the 

 iron contained, its capacity for C0 2 fixation and from direct 

 manometric measurements of the osmotic pressure of its 

 solution if placed in a semipermeable cell). 10 Who would 

 care to undertake to prove that two substances with such a 

 molecular weight are identical! But we have no reason to 

 assume that the differences between different haemoglobins 

 (as far as they exist) manifest themselves by a difference in 

 their iron content and their power of taking up oxygen. The 

 observations bearing on these points, in the author's opinion, 

 are satisfactorily explained by the previously-mentioned ac- 

 cessory factors and by the secondary processes of decomposi- 

 tion; and we doubtless would do well not to unnecessarily 

 make it harder than necessary to comprehend the already 

 complicated circumstance of oxygen fixation in the blood by 

 assuming that there is an unlimited multiplicity of haemo- 

 globins. As 0. Cohnheim ll cautions, since chemists who 

 are disposed to study the physical-chemical balance between 

 haemoglobin and oxygen, work with pure and unchanged 

 haemoglobin, while the physiologists, who have to do with 

 the question of oxygen-transportation in the economy, carry 

 on their researches with blood as little changed as possible, 



E. E. Butterfield, Zeitschr. f . physiol. Chem., 62, 173, 1909. 



10 G. Htifner and E. Gansser, Arch. f. (Anat. u.) Physiol., 1907, 209; 

 E. W. Reid (Dundee), Jour. of. Physiol., 33, 12, 1905-06; J. Barcroft and 

 J. V. Hill, ibid., 39, 428, 1909-10. 



11 0. Cohnheim, 1. c., p. 359. 



