INTRODUCTORY 5 



hsemoglobin molecules in the peripheral portion, with sufficient pre- 

 cision to calculate the molecular weight. The molecular weight of 

 70,000 or thereabouts introduces fresh possibilities as to the differences 

 between one form of haemoglobin and another. The molecular weight 

 which would correspond to an atom of iron is about 17,000, or ap- 

 proximately one- quarter of the true molecular weight. We do not 

 know how the haematin is attached to the globin, but it would appear 

 either that four hsematins are attached to one globin, or four molecules, 

 each of 17,000 molecular weight, are condensed. In either case the 

 process might admit of great variations in detail. The establishment 

 of the fourfold molecular weight leaves us with some difficulties : 



(1) In its relation to oxygen haemoglobin reacts very much as 

 though one molecule of oxygen united with one of haemoglobin. 

 Hartridge and Roughton(25) suggest that possibly in this very large 

 molecule the four haematins may be so far apart as each to unite 

 with oxygen as though the others were non-existent. 



(2) Haemoglobin in its relations with oxygen behaves also as 

 though in solution. This is true whether in ordinary aqueous solution 

 or in the red blood corpuscles. Yet the red blood corpuscles of many 

 animals, if haemolysed even under the most rigorous conditions and 

 without either concentration or dilution of the haemoglobin, shed it 

 as crystalline material. Why should the mere breaking of the structure 

 of a cell throw the material within it out of solution? Presumably 

 in the cell the molecules are not free to orientate themselves at 

 pleasure. The direction of their orientation is in some way decided 

 by the structure of the cell and the whole of the biological aspect 

 is regulated by that orientation. If that be true of the haemoglobin 

 in the red corpuscle, of how many other substances and in how many 

 other cells may it not also be true? 



REFERENCES 



(1) Foster. In an unpublished lecture. 



(2) Henderson, L. J. In conversation. 



(3) The literature is given in the exhaustive treatise, The Crystallography of Haemo- 



glohins, by Reichert and Brown. 1909. 



(4) Douglas, Haldane and Haldane. Journ. Physiol, xliv. 275. 1912. 



(5) VLi:s. Arch, de Phys. Biol. ii. 22. 1922. 



(6) Barcroft, J. AND Barcroft, H. Proc. Roy. Soc. B. xcvi. 28. 1924. 



(7) Anson, Barcroft, Mirsky and Oinuma. Proc. Roy. Soc. B. xcvu. 61. 1925. 



(8) Keilin. Proc. Roy. Soc. B. xcvm. 312. 1925; c. 129. 1926. 



(9) Anson and Mirsky. Journ. Physiol, lx. 50. 1925. 



