In October 1979, a technician in the electron microscopy laboratory of one of the teaching hospitals in Toronto spilled a bottle containing approximately 500 ml of 2% osmium tetroxide. He asked for help, and four other technicians were involved in the cleanup. They all were exposed to osmium tetroxide vapours for long enough to show signs of acute intoxication. They developed redness and swelling of the conjunctiva, impaired vision, chest pains, breathing difficulties and skin irritation and were taken into Emergency Care at the hospital. The occular symptoms disappeared after two days, but the chest pains and breathing difficulty persisted for approximately one week.

This accident could have had more serious consequences. It has been reported that exposure to osrruum vapour could lead to blindness and serious respiratory trouble. At McMaster University Medical Centre, the safety committee gives precise procedures to be followed in case of accidents with dangerous chemicals. All the occupants of the laboratory have to leave immediately and phone the safety and security team.

At present most medical microprobe analysis is conducted on insoluble particulates such as asbestos fibers in lung tissue. Cryotechniques are not necessary for this type of specimen. Insoluble particulates can be processed conventionally Nevertheless, it is important to emphasize that conventional processing is unacceptable for specimens in which electrolyte distributions in tissues are sought. It is necessary to flash-freeze in order to preserve the integrity of electrolyte distributions at the subcellular and cellular level. Ideally, biopsies should be flash-frozen in the operating room rather than being frozen several minutes later in a histology laboratory. Electrolytes will move during such a long delay. While flammable cryogens such as propane obviously cannot be used in an operating room, liquid nitrogen-cooled slam-freezing devices or guns may be permitted, and are the best way to achieve an artifact-free, accurate tissue sample which truly reflects the in vivo state. Unfortunately, the importance of cryofixation is often not understood.

LaB6 (and CeB6) cathodes are widely used as high-brightness cathodes in a variety of electron beam applications. These cathodes provide about 10 times the brightness and about 100 times the service life of a tungsten filament. However, to fully realize the improved brightness and lifetime of the LaB6 (CeB6) cathode, it must be designed and manufactured specifically for the application.

This article covers tip shape and crystal orientation. Future articles will deal with materials selection, preparation, purity, composition, and cathode operation.

The design of the LaB6 cathode tip is critical for maximum lifetime and optimum performance. The cathode must also provide the appropriate source size, beam current, and beam brightness for the application.

The lifetime of the LaB6 cathode is limited by three basic factors: cathode temperature, vacuum pressure, and tip shape. The first two factors are critical and depend on proper user operation. Poor vacuum and excessive temperatures accelerate LaB6 material loss, which decreases the cathode lifetime. The third factor, tip shape, is also critical, and careful production control ensures that the tip shape is optimized.

There is a gap between biochemical findings and ultrastructural interpretation of “glycogen granules”. Biochemists have recognized that glycogen contains covalently bound proteins. These include enzymes involved in giycogen metabolism: glycogenin (protein primer responsible for initiation of glycogen synthesis), glycogen synthase and phosphorylase, and presumably other regulatory enzymes. The structures formed by the association of glycogen and protein have been called protein-glycogen complexes, considered as proteoglycans, or as dynamic cellular organelles, glycosomes.

The question arises as to why the biochemical recognition of a protein component in glycosomes has not been acknowledged in electron microscopy (EM)? This protein is visible in every section stained by uranium (U) and lead (Pb) salts where it appears as 20-30 nm granules (Fig. 1). However, these granules are commonly interpreted as glycogen, despite the fact that glycogen does not react with ionic compounds and therefore cannot be stained by U-Pb.