A Microtome Sectioning Technique for Electron Microscopy Illustrated with Sections of Striated Muscle

Abstract

The preparation of histological and cytological sections for study with the electron microscope presents several difficulties. These are due chiefly to the necessity of drying and to the low penetrating power of electrons. 1 The distortion commonly attendant on air-drying can be obviated by vacuum-drying in the frozen state. The low penetrating power of electrons is more serious since for high resolution electron micrographs it has been found that sections must be less than 0.25 ν and preferably less than 0.1 ν thick. 2 von Ardenne 3 has described a method, but, judging from the one micrograph published, his sections were not sufficiently thin for good resolution or adequate penetration. The present paper describes a technique by means of which relatively uniform 0.1 ft sections of striated muscle have been prepared and examined with 60 kV electrons.

Some types of material can be cut freehand 2 but much histological material requires a microtome. No commercial microtomes cutting such thin sections are now available but standard commercial models can be adjusted by a number of different ways to cut thinner sections. Our machinists have suggested three methods for adjusting microtomes to cut at fractions of a micron: (1) For Minot and similar sliding microtomes the cam knob that hits the setting device to control the movement of the ratchet wheel may be machined so that it has 4 quadrants each with a different radius. The radii can be adjusted so that with the machine set to cut at one micron the micrometer screw moves only approximately one-quarter of a micron (one-quarter of a tooth-spacing on the ratchet wheel) at a stroke, the cam knob being turned by hand between strokes. (2) The single micrometer screw used to move the specimen may be removed and replaced by a differential screw.