4 ERYTHROCYTES 263 



shape. Ponder (1954) obtained the image shown in Fig. 132 by a 

 series of microphotographs with an objective of the least possible 

 focal depth. With retention of the volume, the transformation to 

 spheres is effected by surface changes only. For instance, the biconcave 

 erythrocyte of the rabbit has a surface of no fi^, whereas that of the 

 globular form is only 70 fi^ (reduction in surface of 36%). 



A further indication of surface changeability is provided by the 

 dented blood corpuscles, which are transitions between the biconcave 

 discs and the globules, or the curious thorn-apple forms which arise 

 vmder certain conditison. These facts make it plain that surface forces 

 are responsible for the shape of the erythrocytes. Gough (1924) points 

 out that surface-enlarging forces must be active in the erythrocytes, 

 conducive to expansion of the surface of contact with the suspension 

 liquid, as in the case of the myelin forms. The largest surface would 

 be obtained if the blood corpuscle were flattened to the thinnest 

 possible disc. On the other hand, there is some shght surface tension 

 in the blood corpuscles (presumably of the order of i dyne/cm, cf. 

 Table XXI, p. 166), tending to reduce the surface and to round off 

 the erythrocytes if other factors do not interfere. 



Now it mav be that the exceptional shape of the erythrocytes of 

 mammals represents some kind of equilibrium between the surface- 

 enlarging and surface-reducing forces. If that be so, the membrane of 

 the erythrocytes should have the properties of a mesophase. No form 

 of equilibrium can, however, be mathematically computed from the 

 cross-section in Fig. 132 and Ponder (1934, p. 89) therefore inclines 

 to the belief that there must be a certain amount of internal solidity. 

 The micrurgical investigations of Seifriz (1927, 1929) tend to endorse 

 this, for they show that deformed and elongated erythrocytes have 

 some slight elasticity. Dervichian does not agree with this view 

 (Dervichian, Fournet and Guinier; 1947). 



Inner structure. The various theories as to the internal structure of 

 the red blood corpuscles are expressed in the following two views. 

 One school regards the anucleate erythrocytes as enclosed in a mem- 

 brane which gradually changes towards the interior into a very loosely 

 knit spongy structure, in which the red blood pigment is embedded. 

 Some support for this view is afforded by the network structure which 

 can be made visible in young erythrocytes by suitable fixation and 

 staining. Representatives of the other school of thought, however. 



