Spherical and chromatic aberrations have been the bane of optical lenses ever since they were first ground from a piece of glass. As light travels through a convex (converging) lens, the rays at the center of the optical axis are refracted (bent) less than the peripheral rays, so that the central rays are focused behind the peripheral rays. This is the essence of spherical aberration. Light of differing wavelengths (colors) interact differently with the lens so that longer wavelengths (red) are focused behind shorter wavelengths (blue). This is chromatic aberration. In the early days of light microscopy, these two inherent flaws seriously limited the quality of images.

When an electron passes through matter, the energy of the electron is transferred to the material in the form of ionizations and excitations. Almost all of this transfer is the result of the Coulomb interaction of the beam electrons with the electrons in the specimen; that is, scattering of beam electrons by nuclei is not an important energy-transfer process.

On average, about 30 eV is transferred for each ion pair (the electron and the parent atom) produced, and most of the energy transferred goes into primary or secondary ionizations. In a typical energy-loss process, an electron can be removed from an inner shell (it can leave the atom with a velocity comparable to that of the incident electron).

Virtually all animal cells contain organelles called glycosomes which until now have been neglected in cell biology. This author recently published a comprehensive review article entitled "Glycosomes - the organelles of giycogen metabolism", Tissue & Cell 28 (3) 253-265, 1996. The review, based on biochemical and microscopy data, includes a complete history of giycogen research and the current status of knowledge

Biochemical studies on giycogen metabolism demonstrate the existence of a complex enzymatic machinery involved in giycogen synthesis and degradation, which constantly accumulates giycogen and releases glucose. Such types of cellular machineries represent cell organelles and these were already called glycosomes.

Advances in the biological sciences have given rise for the need to visualize microscopic structures of interest. As the requirement to see specific structure and sub-resolution details arise, investigators have turned to fluorescent probes to label and observe these details, which are often undetectable using conventional methods in light microscopy. Fluorescence microscopy offers many advantages for visualizing specific structure and sub-resolution details, which are often undetectable using transmitted light microscopy. Recent advances in fluorescent probe and microscope design, as well as imaging instrumentation designed for fluorescence applications, are now permitting life-science researchers to view details in regions of interest with increasing precision, accuracy, and resolution.

Liquid crystals are substances which combine properties of both liquids and solids. To investigate the structures and slructurai defects of liquid crystals, freeze fracturing of these gel-Like substances has been performed successfully for many years. In the TEM the structures of the different types of liquid crystals have been investigated and the results confirmed the earlier investigations using polarizing light microscopy. These TEM studies extended the knowledge of structures and structural defects of this fascinating state of matter. However, freeze fractures were only carried out on liquid crystals which form around or below room temperature.

Microscopists in today's laboratories face multiple challenges. Many must examine specimens according to legal, governmental or grant-specific requirements. Protocol requires that the specimens be documented by conventional photography, electronic imaging techniques, or both. Because of the thousands of specimens examined, operators work under conditions of potential physical strain for hours at a time. And the material they examine requires that they have expertise with large and complex imaging instruments.

For numerous reasons a closed-circuit water cooling system is the preferred option for providing cooling water to the electron microscope. Cooling water is required by the electron microscope to cool the diffusion pumps and to keep the electronics' and coiumn temperature stable.

A closed-circuit water cooling system is essential if the local water supply has a high chloride concentration, has floating particles, is acidic, has a water temperature that fluctuates and is uncontrollable. This potentially leads to specimen drift problems in the TEW, and/or has a water temperature that is very cold. This potentially leads to condensation problems or diffusion pumps not functioning properly in the TEM.

Pretreatment of epoxy thin sections with strong oxidizing agents such as hydrogen peroxide, sodium methoxide, and sodium m-metaperiodate facilities the location of antigens with immunostaining procedures. Etching, or pretreatment, of sections unmasks antigenic sites on glutaraldehyde fixed and postosmicated tissue, partially removes osmium bonds, temporarily decreases the hydrophobicity of the epoxy surface layer of the section, reduces the electron density of the tissue and increases resistance to heavy rnetai poststaining.

Manfred von Ardenne was an EM pioneer and the first to publish a complete concept of a scanning electron microscope. A German overseas newscast reported the death of Manfred von Ardenne on 28 May. During the 1930s he was involved in cathode ray work and later lived In East Germany and did significant cancer research. Not mentioned in the newscast was his conceptual development of the SEM in the late 1930s.

He outlined the underlying principles of SEM operation: an electron probe scanning a small region of [fie specimen, the emitled electrons are captured, amplified and time-sequentially displayed on a cathode ray tube. Magnification is the ratio between the areas scanned and displayed His was the fantastic notion of a microscope without a magnifying lens.

This article outlines how projection x-ray microscopy can be used to view the structures that develop within solidifying metals during the freezing process (in real-time and in situ), A description of x-ray microscopy methods will be given. The specialized furnace design and techniques required to permit observation of solidification phenomena will also be described. This forms the outline of the salient features of our X-ray Transmission Microscope (XTM) for solidification studies. This instrument is being developed for microgravity materials research at NASA's Space Science Laborataory in the Marshall Space Flight Center, Alabama. Finally, a sampling of radiomicrographs taken during alloy solidification will be presented.

Performing X-ray analysis on a sample in an SEM used to be relatively straightforward. Straightforward and not always very exciting. Things have gotten a lot more interesting, In jus! the past few years, the amazing development oi variable pressure SEMs has revolutionized the way we can look at samples. At the same time these new machines have changed the way we can image samples, they have also affected how we perform X-ray analysis on those samples.

I apologize in advance for the following gross simplification. For quite a lot of samples, the point and click method of X-ray analysis was and is sufficient to get meaningful data from a sample. Put the beam on a feature, collect a spectrum, and move onto the next sample.