Polymerization of n-butyl methacrylate monomer is used as a rapid and simple means for embedding fixed biological material. The solid resin provides an optically clear matrix for cutting very thin sections, one at a time, with a slightly modified conventional rotary microtome. Advance of the embedded specimen toward the knife is obtained from the thermal expansion of a brass specimen holder. These ultrathin sections have uniform thickness, large area, and integrity of tissue structure. They are suitable for producing transmission images at the higher magnifications of the conventional light, phase-contrast, and electron microscopes. Metallic shadowing of the sections provides greater contrast as well as a threedimensional aspect to the structural details of the tissue. Micrographs and a bibliography are presented.
Some of the very remarkable properties of the protoplasm of living cells must be related to the basic structure of the fibrous gels of which it is composed. The free and purposeful movement of the organized structures and of different cell components, apparently differing in function, can now be visualized and studied quite well with advanced methods of physical optics. By the proper use of phase optics and time-lapse photomicrography,' a remarkable comparison of the living cell's composition and structure can be made with similar but fixed structures examined in the same or an homologous cell, a t much higher powers, under the electron microscope.2-3 9A series of static images and short motion picture scenes were used to illustrate some of the similarities and differences in the structural organization and the behavior of various components of the tumorous cell strain of the rat (T-333) derived in vitro from a normal fibroblast strain 1 4~.~ Cinephase studies were also made of the 23-year-old strain of human chondromyxosarcoma, strain D-1 Re; of the 15-year-old human fibrosarcoma, strain A.Fi.; and of the 3-year-old strain of human epidermoid carcinoma of the cervix, strain HeLa, when grown in thin tissue-culture slides.These motion pictures show clearly the structural transformations of the very active superficial plasmagel layer of these cells. Coarse fibrous processes and fine microfibrils, especially numerous in the normal strain 14p cells, reveal their long filamentous character as shown in PLATE I, FIGURES 1 and 2, and reveal their narrow dimensions (some about 0.2 microns in diameter). These microfibrils show their remarkable ability to grow rapidly in crystalline fashion, then stiffen and often break off, or even "deliquesce" into the receding less polymerized or solated base from which they originally appeared. In PLATE I, FIGURE
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