Recent developments in methacrylate embedding. II. Methods for the sectioning of optically selected single cells, the orientation of the plane of sectioning and the identification of the region of the specimen included in the sections.

The almost insignificant volume of a cell or tissue that is included in a thin section, as well as the small number of cells that can be made available for examination in the electron microscope, makes it desirable to have techniques that would permit the serial sectioning, in a known plane, of specific regions of optically selected individual cells or small portions of a tissue. Such techniques would not only make possible three-dimensional reconstructions of fine structure but would also eliminate the tedious examination of large numbers of sections that is now required for adequate study of many histological or cytological details. The ability of the Porter-Blum microtome (1) to cut long ribbons of thin sections of relatively uniform thickness (250 to 500 A) has stimulated the development of techniques for deliberately mounting ribbons of serial sections for examination in the electron microscope. Williams and Kallman (2) and Gay and Anderson (3), working independently at opposite sides of this country, have devised adequate methods for mounting serial sections. In this report, a technique is described for the sectioning of a single optically selected cell in a colony of cells grown in vitro, with precise knowledge of the plane of sectioning and positive identification of the region of the cell included in the sections. Modifications of this technique extending its usefulness to many other types of specimen are also described.