Use of a Glass Edge in Thin Sectioning for Electron Microscopy. ∗

The use of a steel microtome knife in cutting sections for electron microscopy has certain disadvantages, especially in the achievement and maintenance of a sufficiently sharp edge, which involve a considerable expenditure of time. The search for a knife material having homogeneity and hardness without excessive brittleness led to the development of a glass cutting edge. With it, we have been able to cut thin sections more consistently, easily, and rapidly than with steel microtome knives. Since the glass “knives” are obtained simply by breaking them from a strip of glass, the tedious and uncertain sharpening procedures necessary with steel knives are eliminated. Inspection with the light microscope reveals a smoother and, we believe, sharper edge. Fewer grooves or scratches are found on the face of a block of tissue after it has been cut with the glass edge. The glass knives are also quite inexpensive. The knives are made by breaking a strip 11/2″ wide and about 12″ long from a sheet of plate glass approximately 3/8″ thick. Since the edges thus produced will form clearance facets, this fracture should be as smooth and straight as possible. A series of straight parallel scorings at 45° to the long axis are then made on each strip, 1″ apart, and on the opposite surface from the first scoring. The parallelograms thus outlined are broken off, producing a set of glass blocks, each of which has two cutting edges 3/8″ long, formed by faces meeting at a 45° angle (Fig. 1,A). Any competent glass cutter with standard equipment can produce these knives from stock plate glass for something less than 25 cents each. Straighter edges, however, can be more regularly secured with a diamond-point scriber having constant spring tension (designed by Robert C. Jackson of the Department of Biology Machine Shop), utilizing a controllable pressure device, such as an arbor press, to break off the knives.