ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04624.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYThin layers of pure water or aqueous solutions are frozen in the vitreous state or with the water phase in the form of hexagonal or cubic crystals, either by using a spray‐freezing method or by spreading the liquid on alkylamine treated films. The specimens are observed in a conventional and in a scanning transmission electron microscope at temperatures down to 25 K. In general, the formation of crystals and segregation of solutes during freezing, devitrification and evaporation upon warming, take place as foreseen by previous X‐ray, thermal, optical and electron microscopical studies. Electron beam damage appears in three forms. The devitrification of vitreous ice. The slow loss of material for the specimen at a rate of about one molecule of pure water for every sixty electrons. The bubbling in solutions of organic material for doses in the range of thousands of e nm−2. We propose a possible model for the mechanism of beam damage in aqueous solutions.The structural and thermal properties of pure frozen water important for electron microscopy are summarized in an app

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04625.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYScattering cross‐sections for the interpretation of the scattering‐absorption contrast of microscopical images of amorphous biological specimens are calculated. The constituent atoms are treated as independent particles and their atomic potential is approximated by a modified Lenz‐Wentzel potential. Both elastic and inelastic scattering processes are considered. Formulas of the effective elastic and inelastic atom scattering cross‐sections are derived for both a CTEM with hollow‐cone illumination and a STEM using an annular detector. The scattering‐absorption contrast is plotted as a function of the atomic number for a CTEM applying parallel illumination and a STEM using a dark‐field detector with maximum collection efficiency. The presented results are valid for acceleration voltages U in the range 20 kV

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04626.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYThis paper describes a method by which automatic image analysis can be applied to the study of size distributions of small (<5 nm) radiation induced bubbles. Statistically valid results are obtained directly from transmission electron microscope negatives and the optimum imaging conditions for obtaining reliable data are discussed.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04627.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYA method for measuring the emission spectra from regions of neuronal lipopigment in tissue sections is described and illustrated. Each emission spectrum was derived from the means of six sets of readings, from either six regions of lipopigment from six neurones which were presumed to be from a homogeneous cell population, or from one region of one neurone. Characteristics of the emission spectra from lipopigment in various forms of neuronal ceroid‐lipofusinoses (NCLs) and in brains without evidence of NCL are presented and discussed. The results indicate that the classification of lipopigments should not be restricted to the two categories of ‘lipofuscin’ and ‘ceroid’.This method may aid the identification of various pathogenic mechanisms in neurones, and provide another means of investigating the effects of certain drugs on cerebral

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04628.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYA general method for obtaining representative samples of particulate suspensions for morphologic evaluation is presented. The key to the method is the orientation of a suitable substrate for sample collection normal to an applied centrifugal field. Precise orientation is achieved by floating the substrate on a dense water‐immiscible fluid of low viscosity. Centrifugation may be performed in common angle‐head centrifuge rotors.Two variations of the method are described which permit direct visualization or embedding of the particulate sample. Both variations are simple, can be performed routinely, and require only small amounts of material. They can also be performed simultaneously with centrifugation of the bulk samp

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04629.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYOne of the most important problems in tissue preparation for electron microscopic analysis at a molecular level involves the preservation of the tissue without introducing extensive denaturation of the proteins. Low temperature is a most efficient condition for the inhibition of protein denaturation and freeze‐drying offers favourable conditions for transferring proteins to a dry state with minimal denaturation of the proteins. However, the embedding of the dried tissue in a plastic leads to extensive denaturation of the proteins when performed in the conventional way. This eliminates very efficiently the advantages of the method. The situation becomes even worse when subjecting the tissue to freeze‐substitution. To eliminate as far as possible the denaturing effect of plastic embedding, freeze‐drying can be combined with low temperature embedding in a plastic.Freeze‐fracturing allows a most efficient use of low temperature to reduce conformation changes in proteins. The value of the freeze‐fracturing technique depends entirely on a precise knowledge of the location of the fracture planes. Since this location is not known, it must be determined on the basis of a deduction. If this deduction is wrong, the method becomes misleading. Two methods which allow a certain testing of the correctness of the deduced location of the fracture planes are

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04630.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYFrog retinas were examined following cryoultramicrotomy. The extent of glutaraldehyde cross‐linking ranged from maximally 2% for 2 h to no cross‐linking. When the tissue was cryo‐protected, the effects of hypotonic, isotonic and hypertonic media on outer segment banding periodicities were studied. The specimen was cryosectioned at 193 K to 113 K with sections collected on a dry knife (213 K to 123 K). The sections were freeze‐dried and only rehydrated with phosphotungstic acid section stain when transmission electron microscopy was used to establish the extent of gross retinal morphology for each fixation protocol employed. As the extreme of no cross‐linking and no cryoprotection was approached and reached, conventional sections which displayed extensive retinal morphology were not obtained. Instead, fragments of retinal tissue resulted which showed periodicities of alternating light and dark bands. These periodicities are interpreted as photoreceptor outer segment discs with contrast formation depending upon an interplay between three factors: mass density differences between disc and interdisc space, section cutting angle, and section

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04631.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYCultures of porcine granulosa cells have been grown on serum coated carbon films deposited on glass coverslips. Intact and detergent‐treated cultures were critical point dried, chromium shadowed and removed from the coverslips by dilute hydrofluoric acid. Whole cell mounts were examined by conventional transmission electron microscopy. The advantage of this system over other methods includes the ability to: (1) examine cells with a highly rounded morphology, (2) use high cell densities, (3) study cell projections extending onto the substratum, (4) maintain cultures for long periods, (5) examine large samples easily, and (6) readily use the same cultures for transmitted light and fluorescent microscopy, scanning and transmission electron microscopy (SEM and TEM

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04632.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARYThree fixation schedules were devised and compared in terms of their influence on the preservation of mucus and surface‐associated microorganisms contained within it. Different mucus‐secreting epithelial tissues from normal and spoiled oysters and normal rats were examined by scanning and transmission electron microscopy and light microscopy. On all tissues, mucus was best preserved in specimens fixed by 10% acrolein vapour for 1 h then immersed in 3% glutaraldehyde—3% formaldehyde fixative containing 0·05% ruthenium red, cacodylate buffer pH 7·4, for at least 3 h. This fixation schedule also greatly increased the preservation of microorganisms in mucus in specimens from spoiled oysters and normal rats. In contrast, the retention of mucus and surface‐associated microorganisms was poor in tissues fixed either by 1% OsO4vapour for 1 h followed by immersion in combined aldehyde fixative, or by direct immersion.The quality of preservation of the mucus layer, epithelium and sub‐epithelium was also noted by transmission electron microscopy in tissues prepared by the different fixation schedules. Cellular preservation was satisfactory in directly immersed tissues but poor in vapour fixe

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1982.tb04633.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY