ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03935.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYIn respect of instrument design two main developments are taking place in high voltage electron microscopy: towards even higher operating voltages (3–5 MV) and towards higher resolving power at moderate voltages (250–600 kV). Applications of existing instruments (650 kV‐1.2 MV) are still primarily in metallurgy, especially for radiation damage studies, but their usefulness for biological research is now being actively explored. Microchambers have been developed for observing specimens, both metallurgical and biological, in a controlled gaseous or liquid environment. The prospects for observing living material, except at low magnifications, remain very doubtful on account of ionization effects, but informative work with wet specimens should be pos

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03936.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe scanning transmission electron microscope is of quite recent origin, and it is only in the last few years that it has been shown that this instrument is capable of giving the same high resolution as the conventional electron microscope. In this article we examine the conditions necessary for the achievement of high resolution and also the various modes of contrast which can be obtained from this instrument. Finally, we suggest other ways in which the microscope can be used in future investigations.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03937.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYA brief historical survey of the origin of stereological methods is followed by a synoptic characterization of their nature. They fall into two main classes depending on the structural models at their origin. Those methods which aim at a size analysis of the particle population provide more information, but are more subject to limitations, than those which estimate bulk parameters of the structure as a whole. The choice between the different methods must be guided by a clear definition of the most informative parameters and of the geometric properties of the structure.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03938.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYMethods are described for the use of a sensitive photomultiplier, improved photomultiplier voltage supply circuitry, quartz lens and a half‐parabolic mirror to increase the amount of light collected from a luminescing specimen examined in the scanning electron microscope. The combined effect of these improvements increases cathodoluminescence detection twenty times. Sources of background light are investigated and recommendations are made for decreasing this noise component, which seriously limits sensitivity of cathodoluminescence signal detection.An appendix describes the natural luminescence (autoluminescence) of plant tissues under the impact of the electron beam. The biological applications of this mode of scanning microscopy have been little explored, but autocathodoluminescence is found to be of wide occurrence in plant tissue

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03939.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYIn high‐resolution dark‐field microscopy thin carbon films present an appearance with many bright spots with sizes down to 0.3–0.5 nm which, by their presence, seriously interfere with the extraction of biological information. The nature of these spots has so far remained unexplained. It is shown that these spots are sharpest at an overfocus of about 275 nm with respect to the bright‐field focus condition. An explanation is presented here which accounts for both the focus difference and the otherwise inexplicable phenomenon of the small size of the spots. In the proposed model the bright spots are associated with small crystals present in the carbon film which give rise to Bragg reflection of electrons into the acceptance angle of the dark‐field geometry. Due to a constructive interference the Bragg‐reflected coherent electron wave fronts produce, behind the object, high‐intensity maxima with sizes equal to about × 1/5 the diameter of the scattering crystals. These maxima are now thought to produce the bright spots usually observed in dark‐field electron microscopy. The interference effect is illustrated with pictures of an

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03940.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYDNA molecules bind to carbon films placed on the surface of aqueous solutions and are extended and oriented by the flow forces on removal from the surface. The number of molecules bound increases with ionic strength suggesting that the bonding is hydrophobic.If carbon films are subjected to ionic bombardment in a flow discharge, they can be modified so that molecules bind strongly, and are deposited in a tangled, random‐coil configuration, uninfluenced by flow forces. The strength of binding is decreased by reducing the discharge time and current, and by addition of salt (NaCl), suggesting that the bonding is ionic. When weakly bound, the molecules are condensed by ethanol. The strength of binding can be adjusted so that the molecules are largely untangled by flow, and in a form suitable for the mapping of bound enzymes, or other identifiable markers.Aggregation and extension of molecules, that occur on unmodified films, and the binding of cytochrome c, that occurs in methods based on that of Kleinschmidt&Zahn (1959) are avoided. Both double and single‐stranded molecules can be deposited and seen after rotary shadowing with Pt. The discharge can be performed in a vacuum produced by a standard oil‐filled rotary

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03941.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYPossible hazards in the use of optical spatial filtering applied to the analysis of electron micrographs are illustrated. Two experiments show how information is either lost or spuriously introduced into reconstructed images of micrographs when (a) only one part of a two‐part micrograph image is reconstructed and (b) when noise is eliminated from the reconstructio

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03942.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYFixed and embedded normal rat peritoneal mast cells were studied by light and electron microscopy, utilizing stereological methods to obtain quantitative data on their structure. The diameters of the mast cells and their nuclei averaged 10.9 and 5.8 μm respectively. The volume of the individual mast cell granule was estimated to 0.3 μm3. About 53% of the cytoplasmic volume was occupied by granules, and 2% by mitochondria. 11% of the cell volume was taken up by the nucleus. The average number of granules per cell was calculated to about 1020. Quantitative biochemical data on mast cells, extrapolated from the literature and applied to the calculated figures above, yield the following results with respect to mast granule contents‐heparin: 95 × 10−3pg, histamine: 30 × 10−3pg and 5‐hydroxytryptamine: 1.3 × 10−3pg per mas

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03943.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYA histochemical technique has been used in scanning electron microscopy to localize specific areas in biological material. The specific contrast introduced by the staining procedure depends on the interaction of complex variables such as the coating material, the accelerating voltage and the use of a primary or secondary electron signal.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03944.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY