Abstract
The beam of a 50-kv electron microscope does not penetrate specimens that are thicker than 0.1 μ. Thus, in order to study biological specimens with this type of microscope we have further developed the technic described by Pease and Baker, 1 who altered a Spencer Rotary Microtome (model 820) by adding a wedge to the mechanism for forward movement. We reduced the angle of the inclined plane surface by a factor of 10 to 1 so that each step is 0.1 μ rather than 1.0 μ.
Since forward movement results from a pin in sliding contact with an inclined plane surface, it is important that the surface of the plane be as nearly perfectly flat as possible. The accompanying photograph, Fig. 1, illustrates the means by which the problem of a flat surface for even forward movement was solved. At the left of the picture (A) the original plane can be seen. The reduced angle is shown by D. The light gray triangular area (B) is an angle-reducing block of steel, to which is fastened an optical flat (C). A brass disc (E) instead of a pin is used for the feed screw tip. Horizontal movement of the disc is responsible for forward movement of the specimen. Vertical movement of the flat and the mechanism to which it is attached causes the slicing action of the microtome. Since the disc and flat are held firmly in contact by a spring, any irregularities in the surface of the plane will be evident on the sliced section.
Since the ordinary microtome knife cannot be used to cut sections as thin as 0.1μ, ours was especially made,∗ hollow ground on both sides, with a long bevel.
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