The measurement of mass, thickness, and density in the electron microscope.

A description is given of quantitative methods using the electron microscope which can be applied to specimens with much smaller dimensions than those which can be used with the established cytochemical methods based on the use of the interference microscope and the techniques of ultraviolet and x-ray absorption. A discussion of electron scattering shows that under chosen operating conditions in the electron microscope the effective total mass-scattering coefficient S of a specimen is almost independent of its chemical composition. An order-of-magnitude agreement is observed at four accelerating voltages between experimental total scattering cross-sections for polystyrene and theoretical values for carbon.

A quantitative estimation of the uptake of two new electron stains by the cytoplasmic membrane of ram sperm.

From microdensitometer measurements on electron micrographs of sectioned sperm heads it has been found that the electron stains, triiodobenzoyl chloride, and triiodophenylisocyanate, increase the image contrast of the cell membrane above its immediate background by about 40 per cent and 70 per cent respectively, while the nucleus remains unstained. Assumptions based on current electron scattering theory have been used to deduce the uptake by weight of the stains in terms of the density of the nucleus, which was estimated from complementary measurements made with the interference microscope and electron microscope. The uptake of the stains was found to be about 7 per cent and 12 per cent by weight respectively.