Simplified Embedding of Biological Material for Thin Sectioning

Abstract

SINCE the introduction of thin sectioning by conventional methods for electron microscopy in 1948 ¹, several embedding techniques have been described^1,2. In one of these, namely, double embedding in nitrocellulose and paraffin, the tissue is first infiltrated with an ether–alcohol solution of nitrocellulose ; the volume occupied by the solvent is then filled with molten paraffin. The chief disadvantage of this method is the slowness of infiltration of the viscous nitrocellulose. In addition, the hardness of the block cannot easily be controlled to suit the hardness of the material to be cut. The second method in common use consists in embedding the material in a plastic such as butyl methacrylate, which is then polymerized in the temperature range 50°–60° C. for 12–24 hr. to form a hard mass. We find, however, that the polymerization is difficult to control. The hardness is governed by the degree of polymerization, and the cutting qualities are quite sensitive to hardness. Furthermore, the hardness appears to increase with time, making storage of the blocks impractical.