Francis W. Bishop

Form and dimensions of isolated hyaluronic acid.

1. 1. A highly purified sample of the sodium salt of hyaluronic acid (HA) was prepared free of contaminants from the vitreous humor. 2. 2. The HA was studied by ultracentrifugation, light scattering, streaming birefringence and electron microscopy. All of the data could be interpreted in terms of an asymmetric molecule of particle approximately 6,000 A in length which contracted to approximately one half this value in the presence of ions. 3. 3. The data indicate a polydisperse material of weight average molecular weight 1.27·106. 4. 4. Electron microscopy revealed thread-like particles which were sensitive to the depolymerizing action of hyaluronidase. The particles were intermediate in form between a stiff rod and a flexible coil. There were no large spheres present and the dimensions and form seen in electron microscopy were in agreement with similar values deduced by light scattering and streaming birefringence studies.

Use of a Platinum Filament in the Electron Microscope

A platinum filament covered with a mixture of oxides has been used to replace the tungsten filament in the RCA model EMU‐2 electron microscope. This unit originally was used on an Akashi electron microscope. Since the filament operates at a low temperature, evaporation of the filament itself is very slow. The electron source is very small. The drift of illumination is small and the field of illumination is quite uniform.

Unusually Highly Biased Gun on the Electron Microscope

A self‐biasing arrangement is described whereby the beam current of the electron microscope is decreased to less than 5 μa. This reduction of beam current reduces the contamination rate and the heating of the specimen and at the same time improves the illumination. A further combination wherein the bias can be adjusted from the control panel is described. The smaller aperture in the condenser system which is made possible by this system reduces the angular aperture of illumination and increases the depth of focus and resolution.

New Automatic Sharpener for Microtome Blades

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.

A New External Objective Aperture Centering and Interchanging Device for the RCA EMU Electron Microscope

A device which quickly interchanges and centers up to seven objective apertures in the electron microscope has been described. It consists of a platinum‐iridium, aperture‐carrying tongue which may be moved longitudinally and laterally through a sylphon bellows arrangement. The interchanging and centering of an aperture takes only seconds since its position can be observed on the final viewing screen. It is believed that these apertures remain cleaner over a much longer time than in the usual aperture arrangement since they are retracted to a shielded position until actually used and only one of seven apertures is in the beam at any one time. With no aperture in place the entire specimen screen may be scanned at low magnification so that the search for suitable fields is simplified. Then the proper aperture for the degree of contrast desired is moved into place and exposures are made in the usual way. The device has greatly simplified the use of objective apertures in the electron microscope.