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An automated image acquisition and analysis system has been developed that rapidly determines regional blood flow by using the locations of fluorescent microspheres deposited in tissue. A motor-driven microtome removes sections of frozen tissues in steps variable between 10 and 100 μm. Filtered light excites microsphere fluorescence from the exposed surface of the remaining tissue block. A charge coupled device camera records fluorescence images from the tissue block surface after removal of each slice. Approximately 450 images are analyzed from perfused rat hearts providing precise x, y, and z locations of about 10 000 microspheres. Image analysis of fluorescent microspheres is much faster and less labor intensive than traditional indirect microsphere-based flow measurements while providing higher quality data.

Conventional methods of sharpening involve extensive grinding which is primarily for the removal of large nicks but which serves the additional purpose of fitting the knife to the sharpening means. Since large nicks rarely occur in ultra‐thin microtomy, the grinding would become unnecessary if the fitting of the knife to the sharpening means could be made permanent. A permanently attached short sharpening back is described which makes this possible. Using the finest abrasives and polishing powders and prepared glass plates as the sharpening surfaces, it is possible to resharpen a knife in less than ten minutes. The method is described in detail.

Two forms of a high speed type of microtome are described which are able to cut cross sections to the thinness required for electron microscopic study (0.1 to 0.8 micron, depending on the material). Techniques of microtome operation are suggested together with a few methods of sample preparation and subsequent section treatment, namely, collecting, selecting, and mounting. Embedding materials which sublime readily are described; these have been used successfully with this high speed microtome to support many types of materials. These volatile embedding materials have the advantage that they eliminate the difficulties that on some occasions arise with the use of solvents in the process of solvent extraction of embedding materials, such as Carbowax and paraffin, from the sections. A number of photographs are shown of the high speed microtome as well as electron micrographs of a few sections produced by the instrument. These pictures of rubber, rayon, Lucite, block Nylon, and animal tissue indicate some of the fields of application of the microtome and demonstrate the effectiveness of the necessary auxiliary techniques for it, particularly sample hardening and embedding, and section collecting and mounting.

A microtome has been used to remove 2 μ sections from metal specimens as part of a radiotracer diffusion study. The technique is described in detail and includes a design for an orientation stage to obtain sections parallel to the diffusion interface. The equipment has been used successfully on Zr, Ti, Fe, Pd, Ag, and Cu, and diffusion profiles for self‐diffusion in Fe, Zr, and Ag are given. This instrument extends the sectioning method into the area of diffusion zone analysis previously occupied exclusively by abrasion techniques.

A microtome has been built incorporating the principle of deflection of a cantilever to provide the highly reproducible motion necessary in cutting thin sections for electron microscopy. The prototype has been tested, and representative electron micrographs are shown. Alternative designs are discussed. Certain advantages are realized by the application of this principle. A simple construction with a minimum of precise machining readily provides an accurately reproducible motion. No sliding ways or lubricated bearings are needed. The effects of vibration, static friction, and thermal expansion are minimized. The instrument is easily adapted for cutting thin sections for light microscopy.

A new compact microtome knife sharpener has been developed which, in its simplest form, provides a semi‐manual method of sharpening blades for standard and ultra‐thin sectioning. Fully mechanized, however, it eliminates the manual element and requires little attention except to see that the grinding powder and its vehicle are maintained. The knife is caused to move back and forth across an oscillating glass plate by means of a motor drive, and a simple mechanism periodically turns the blade over. It rapidly sharpens a blade capable of cutting ultra‐thin sections for electron microscopy while such an edge is unusually fine for paraffin sections. No stropping or other treatment is required.