ABSTRACT
In a number of papers, I and my collaborators have considered various methods for measuring the volume of mammalian red cells, either in the discoidal 1 or in the spherical form (Ponder & Saslow, 1930a, b, 1931; Macleod & Ponder, 1933; Ponder & Robinson, 1934; Ponder, 1935 a, b). Some of these methods, such as the diffraction method, are applicable to spheres only, and others measure only changes in volume such as occur in hypotonic media. So far as this paper is concerned, the two most important conclusions of the investigations are (a) that the transformation from disk to sphere, whether effected by the addition of lecithin or one of the photodynamic dyes (Ponder, 1936), or by enclosing the cells between two closely opposed surfaces (Ponder, 1928-9), is accompanied by no change in volume, and (b) that at the “critical tonicity” in which haemolysis begins in hypotonic media, the percentage increase in volume is substantially the same irrespective of whether the cells are disks or spheres.
The distinction between the cell envelope and the cell membrane is a convenient one, although it may turn out to be unnecessary. The envelope is the cell wall as a whole, a structure which is visible when stained, and which has a complex ultra-structure (Schmitt, et al. 1936). The membrane is the part of the envelope in which the semi-permeability properties reside, and capacity measurements indicate that it is a layer only a few molecules thick, situated in, or at the surface of, the envelope.
This expression is wrongly printed in Ponder (1935c).
The shape changes shown in Fig. 3 of Haden (1934) are purely diagrammatic, and do not correspond to what is seen under the microscope. A symmetrical swelling of the red cell in hypotonic solutions is the exception rather than the rule.
The figures for “extended area” in Table II of Ponder (1935a) are less than the figures for the mean area of the discoidal red cells of the various animals, because the measurements were made on cells in systems showing only just beginning lysis.
The values for the ratio length/greatest thickness, however, are 3’56, 4-29 and 2-74 for man, the rabbit, and the sheep respectively, and these are not in the order of the observed resistances. The cell shape, in fact, cannot be defined in terms of one ratio, and what is required is a relation between resistance and some such measure of shape as the “form factor X” which appears in Fricke’s equation for volume concentration as a function of conductance (see Ponder, 19356). I propose to make the necessary determinations shortly.
It must be borne in mind that in all experiments which have been done hitherto, the cells are swelling in hypotonic media as disks, even though the measurements of volume and area are made on the spherical form. Apparent increases in area are thus the result of the method of measurement used, and have no actual existence, for the evidence points to the fact that swelling in hypotonic systems is accompanied by shape changes only, and not by area changes. If we were to lecithinate the cells first, and then put them in hypotonic media, there would be area changes corresponding to the volume changes, but such systems have been used on only one occasion (Ponder, 1936). Cells suspended in lecithin-treated plasma are more resistant to hypotonic media than are cells in untreated plasma, but the increase in resistance is due to a decrease in the R value rather than to an increase in the critical volume.
