The diffraction method of measuring the diameters of erythrocytes

Abstract

An improved diffraction micrometer is described, the theory of the use of this instrument is discussed, and a formula deduced for a haphazard distribution of cells. The method is applied to a variety of size changes of human erythrocytes to determine its reliability. The results show that the method is not reliable for the determination of absolute sizes and, although small changes of size can readily be observed, the measurement of these changes is also to some extent unreliable. The author concludes that the diffraction method is not a reliable means of determining the absolute size of erythrocytes. Changes in the size during the course of an experiment can be followed with considerable delicacy, alterations of the order of 0.3[mu] corresponding to a difference in angle of about 15'', which is quite readable. On the other hand, the measurement of these differences is to some extent uncertain, owing to the formula probably requiring modification for change of shape of the cell. The utility of the method is considerably restricted, owing to the disturbing effect of crenation and rouleaux formation, to avoid which special media are necessary and microscopic control essential. Further improvement seems possible in the provision of sources of mono- chromatic light of great intensity, and in the derivation of the fundamental formula from assumptions that agree better with the known shape of the cell.