ZyO FINE-STRUCTURE OF PROTOPLASM II 



solution does not crystallize? As a matter of fact, every disturbance 

 of the existing equilibrium, say by a hypertonic salt solution or by 

 formation of sickle-shaped cells in anaemic venous blood (Perutz 

 and MiTCHisoN, 1950), provokes the crystallization which is re- 

 cognized by the birefringence of the hitherto isotropic haemoglobin. 

 The possibility exists that in the swollen erythrocyte traces of stro- 

 matin between groups of haemoglobin molecules prevent the crystal- 

 lization which occurs as soon as this stabiHzing system is destroyed. 



Birefringence. Fresh problems arise as soon the optics of erythrocytes 

 is taken into consideration. Rabbit's red cells, carefully haemolyzed 

 by freezing and thawing, are birefringent (Schmitt,Bear and Ponder 

 1936, 1938), exhibiting a very faint polarization cross. With respect 

 to the cell radius, the birefringence is slightly negative in isotonic salt 

 solution, but positive polarization crosses are clearly visible in 

 glycerol mixtures. The inference from imbibition tests of this kind is 

 that, as in the case of the chloroplasts, in the sheaths of the erythrocytes 

 there is positive intrinsic birefringence of the embedded lipids, upon 

 which is imposed a negative form birefringence of the protein frame- 

 work. Lipid solvents, such as butyl and amyl alcohol, produce 

 distinctly negative polarization crosses, abolishing the intrinsic bire- 

 fringence of the lipids and bringing the negative form birefringence 

 out clearly. 



ScHMiTT, Bear and Ponder come to the conclusion that there must 

 be a composite body with alternating protein and lipid lamellae. The 

 lipid layers, they think, must be bimolecular on account of the 

 hydrophiHc bias of the stromatin. This view conflicts with the 

 calculations made by Gorter and Grendel (i92 5)> according to 

 which the lipid content of the erythrocytes would be just sufficient 

 for a single bimolecular covering. The possible layering throughout 

 the stroma would only be lipid-protein-cavity-protein-lipid. Conse- 

 quently, unless those authors' statements are incorrect, it is difficult 

 to see how there can be a composite body of protein and lipid, like 

 that proved for the chloroplasts. 



Another possible explanation, taking the observed facts into ac- 

 count, is that the stromatin is loosely layered and is in itself a Wiener 

 composite body. In this case, too, the positive intrinsic birefringence 

 of the hpid skin overlays the negative form birefringence, the problem, 

 however, still being whether the lipid birefringence would then be 



