Ever since the first embryo was put under a microscope, scientists have been trying to determine which embryonic cells form which structures in the mature organism. Classic methods were to kill (ablate) certain cells and see what structures were malformed or missing when the animal developed. More recently, cells have been labeled with visible tags and the tagged cells traced through development. One problem is that the tag gets diluted by half each time a labeled cell divides. A new labeling method that shows a lot of promise has been demonstrated by David Piston, Robert Summers, Susan Knobel, and John Morrill.

Careful analysis of the composition of the titanium alloys is a very critical part of the overall quality control of all components in modern jet aircraft engines. The engine manufacturing industry is seriously striving for a zero defect rate, which is a very difficult goal indeed. This control is made more difficult by the very reactive nature of titanium when it is heated to its melting point. Titanium reacts with the nitrogen and oxygen in the air to form brittle refractory compounds, so it must be melted and refined in a vacuum. Once these refractories are formed they are very difficult to find or remove and they form the basis for brittle zones in the alloy that can be the initiation site for cracks under the high stress loads found in a jet engine. The presence of nitrogen, in particular, causes a defect called a "hard-aipha", which is an area of nitrogen enrichment containing three to eight percent nitrogen and having a hardness three times that of the alloy.

Orientation Imaging Microscopy (OIM) is a rapid and spatially specific technique for automatically measuring individual crystallographic orientations in a polycrystalline sample. The technique is based on electron backscatter diffraction in the scanning electron microscope (SEM). While the OIM technique has seen many applications to the investigation of structure/ property relationships in polycrystalline materials, with grain sizes ranging from millimeters to submicron, it is not easily applied to the characterization of microstructures at the nanometer scale due to the inherent resolution limitations of the SEM. Thus, a complementary technique for the transmission electron microscope (TEM) would be advantageous for the study of local orientation in submicron structures such as those that exist in nanocrystalline materials and deformed materials.

Reflection microscopy techniques are typically the easiest to employ for routine sample analysis, as they require little or no sample preparation. Included in these methods are reflection- absorption spectroscopy (RAS), which emulates transmission spectroscopy, diffuse reflection infrared spectroscopy (DRIFT), specular or external reflectance, and attenuated total reflectance (ATR). For RAS, DRIFT, and specular reflection, the nature of the resultant spectra is determined by the nature of the sample. These techniques will be discussed in future articles. ATR is primarily a surface technique which provides a high quality absorbance-like infrared spectrum and can be used to readily analyze almost any liquid or solid sample.

There are over 100,000 different proteins in the human body. Each of these proteins plays an important role, such as catalyzing reactions and fighting disease. Researchers at the National Aeronautics and Space Administration (NASA), are looking at the make-up of proteins that are linked to diseases, to lead to the formation of effective drugs to help battle AIDS, diabetes and cancer.

"We are studying the structure of the proteins and how the protein's structure affects its function," says Dr. Russell Judge, a researcher at NASA. "This research will eventually lead to the creation of a drug that interrupts harmful protein activities."

In order to determine the protein structure, scientists have to grow large uniform protein crystals, measure and count the crystals.

A thin, flat section of animal or plant tissue will usually adhere to a clean glass surface and stay in place through the common preparative procedures of staining, washing, dehydration and clearing. The adhesion may be due largely to the close contact between two flat surfaces. This allows very weak non-ionic forces (such as van der Waals forces and hydrogen bonds) between individual atoms, to exist in numbers great enough to add up to a strong attraction between slide and section. Ionic attractions, which operate over longer distances, may also exist between the silicate of the glass (negatively charged ions, especially in an alkaline medium) and basic groups of proteins in the tissue (positive ions, especially in an acidic medium). Unfortunately, not all sections are perfectly flat and not all slides are perfectly clean. Even when these conditions are met, there are some staining techniques that are harsh enough to remove the flattest section from the cleanest slide.

Ruthenium tetroxide (RuO4), which is a stronger oxidizing agent than osmium tetroxide (OSO4), reacts well with some of the more polar lipids that fail to show a reaction with OsO4 . it has been demonstrated that the use of RuO4 can overcome the failure of OsC4 to visualize epidermal intercellular lamellae. RuO4 reacts strongly with both saturated and unsaturated lipid molecules, as well as with proteins, glycogen, and monosaccharides. RuO4 fixed membranes appear thicker than those fixed with OsO4 do4.

RuO4 penetrates tissue very slowly and sometimes uneven, patchy preservation may occur. The use of vibratome sections is recommended to optimize penetration of the RuO4 fixative.

The first article reporting the rising incidence of carpal tunnel syndrome in histotechnologists was written by Pearl Gervais and published in the Louisiana Society for Histotechnology newsletter in 1991. Following that article, the growing interest in the number of injuries within the profession prompted a nationwide survey of histotechnologists. The results of that survey appeared in the first part of a three part article published in the Journal of Histotechnology, 18:139,1995. The articles were written by a group of professionals from the University of Michigan. Carpal Tunnel Syndrome (CTS) was used as the model for potential Cumulative Trauma Disorder (CTD).

During a recent one week "Intensive SEM" course that took place in Johannesburg, South Africa, the students came up with a superb cleaning technique that they wished to report upon. The results are, or should be, interesting to everyone who has to clean a cathode assembly! This note was originally posted on MSA's microscopy listserver and generated several replies. I have included more information below in response to these replies.

Often the most time consuming operation during the routine use of a SEM or TEM is the cleaning of a cathode assembly. The procedure, outlined as follows, requires little operator intervention, is free from possible cathode contamination by the cleaning media, and takes comparatively very iittle time

Microscopy is unique among its analytical counterparts: it requires a hand-eye-brain coordination not needed in any other type of analytical instrumentation. On one hand, manufacturers of microscopes and auxiliary technologies are working to make systems seamless, transparent, and easier to use. On the other hand, microscopists, even those who will use the microscope as routine tools, need to be knowledgeable in their core disciplines as well as fluent in microscopy and sample preparation. It is not enough that a the person running a microscope be trained to "push this button; turn this knob". Especially as we move into the next millennium, it will become increasingly important to understand the light/matter, electron/matter, or probe/matter interactions which occur when examining a specimen. Microscopists of all descriptions will need to know how to optimize both the sample and the technology, how to interpret the information presented by the image, and how to separate artifact from true information. To compound the problem, the convergence of computer, diverse software packages, microscope, camera, and analytical techniques is producing a new type of multiple level information which, in turn, requires expertise in multiple disciplines.