ABSTRACT
Some time ago I published an account of the change in shape, from disc to sphere, which occurs when mammalian red cells, suspended in saline, are placed between a slide and a closely applied cover-glass (Ponder, 1929). Later I briefly described a similar transformation which occurs in plasma or serum to which small quantities of lecithin have been added, the normally discoidal cells again becoming perfect spheres without change in volume (Ponder, 1933), and recently I have observed a disc-sphere transformation in systems containing red cells and dyes of the fluorescein series. To avoid difficulties associated with the peculiar shape of the mammalian red cell, several observers have worked with the spherical form in lecithin-treated plasma (Ponder, 1933, for finding volumes, 1935, in conductivity studies; Race, 1934, in sedimentation experiments; Fricke and Curtis, 1935, in conductivity and capacity experiments) ; no detailed description of the phenomenon itself, however, has yet appeared, and the disc-sphere transformation which occurs with the dyes of the fluorescein series is altogether new.
Calculations of this sort, however, are always open to the objection that few of the more complex dyes are pure substances of known molecular weight.
The volume of cells made spherical by the addition of the photodynamic dyes cannot, however, be found by the photographic method, for the photosensitised cells haemolyse when they are brought into the brilliantly lit microscopic field.
