摘要:

SUMMARYA digital electronic unit is described which, by modifying the video signal of the scanning electron microscope (SEM), permits the selection of images in separate tonal or grey‐scale levels. By the sequential exposure of these grey levels onto colour film with the intervention of colour filters, coloured scanning electron micrographs have been obtained. Full details of the procedure are given. The process is applicable to any normal image capable of being displayed at the scanning electron microscop

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04032.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYA method for microtome sectioning of charcoal is described and optical micrographs of some naturally occurring charcoals are shown. The morphology of charcoal as seen in the transmission optical microscope is very similar to that of wood.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04033.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYA method is described which permits comparative light and electronmicroscopic studies of cell cultures, cell spreads or single selected cells which have been kept in the Plastic Film Dish (PFD). The PFD is a versatile large surface tissue culture chamber which, for electron microscopy, is mounted with a transparent FEP‐Teflon film bottom. Cells are observed, selected and marked on the PFD‐bottom with a high power inverted light microscope. The cells are fixed and dehydrated with a semi‐automatic device while they are stillin situin the PFD. During the preparation steps for electron microscopy the topographical relationship between individual cells and between cells and cell support is accurately retained. After embedding and polymerization the Teflon film is easily peeled off the polymerized Epon, leaving a replica of the mark around the selected cell. This permits relocation of the selected cells for ultrathin sectioning in a plane plan‐parallel to the original cell support. To enable orientated sectioning of selected cells in a plane perpendicular to the cell support, cells are tagged with Letraset‐letters after original embedding and polymerization. Subsequently the re‐embedded polymerized specimens are orientated in the microtome in a position which permits controlled thin sectioning of the tagged cells in the previously sel

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04034.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYMicrodensitometric errors can result from various factors associated with the monochromator system, including imperfect monochromaticity of the light, incorrect setting of the wavelength, and non‐uniform illumination of either the microscopic field or the objective aperture. Certain types of potential error are characteristic of particular instruments. Thus in the Vickers M85 microdensitometer, where the flying spot is the reduced image of a hole situated at the monochromator exit aperture, the interpretation of results obtained with different spot sizes is complicated by the fact that the hole size affects both the spatial resolution and the spectral bandwidth of the system. Similarly, in instruments in which the monochromator exit slit lies in an aperture plane the numerical aperture of the whole system may be affected by the spectral bandwidth andvice versa.Overall instrumental sensitivity is mainly limited at the blue and red ends of the spectrum respectively by the lamp output and the photomultiplier tube sensitivity. Quartz‐iodine lamps are slightly brighter than conventional tungsten sources, especially at short wavelengths, but tend to be less stable photometrically and are more expensive. Simple refracting monochromators and graded‐spectrum interference filters in general pass more light, in the visible spectrum, than do grating monochromators of similar bandwidth.Most errors of wavelength setting can be avoided by routinely measuring at that wavelength, λmax, found empirically to give the maximum absorbance or integrated absorbance. Off‐peak wavelengths can be set reproducibly with the aid of an eyepiece spectroscope, or by adjusting the wavelength so that the absorbance of a given specimen is some precise fraction of that at λmax.The monochromator bandwidth affects the apparent absorbance spectrum of a given specimen, but spectra are not very helpful in assessing possible microdensitometric errors at a fixed wavelength. In probably the best single test of monochromator performance, advisable before any microdensitometry using unfamiliar instrumental settings or staining methods, the apparent absorbance at a given wavelength is plotted against pathlength through a solution having an absorbance spectrum identical with or very similar to, that of the microscopic specimens of interest. Deviations from proportionality between pathlength and apparent absorbance have been found using the graded‐spectrum interference filter of the Barr&Stroud GN2 microdensitometer, but have not so far been demonstrated with the refracting monochromator of the Vickers M85 microdensitometer. Such deviations could result in systematic errors in the comparison of densely‐ and lightly‐stained specimens, and two methods to correct these errors are described. Where the error is a known function of the monochromator slit‐width it may sometimes be possible to use data obtained with two slit‐widths to estimate the ideal result corresponding to monochromatic light. More generally, non‐linearity can be corrected by electronic off‐setting of the photomultiplier tube output. This procedure is analogous with, and if necessary should be carried out together with, a method previously described for the correction of error due to glare. Provided the pathlength and apparent absorbance are proportional over the range of absorbances of interest, results obtained with different monochromator bandwidths can be standardized by multiplication by an empir

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04035.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYThe internal cellular structures of the sheep ventricular myocardium have been comparatively studied in the transmission electron microscope (TEM) and in the scanning electron microscope (SEM). For TEM studies the tissue was prepared according to standard methods. Thick sections (10 μm) of paraffin embedded material were, after they had been deparaffinized in toluene, critical point dried, coated with gold and examined in the SEM. The comparative TEM and SEM investigations revealed very good correspondence, and it is evident that the described preparation procedure for SEM has preserved the fine structures of myofibrils, mitochondria, T‐Tubules and sarcoplasmic reticulum in an excellent life‐like pattern. Of special interest was the three‐dimensional demonstration of triads and of circumferentially arranged T

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04036.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYIce crystal growth was studied in rapidly frozen skeletal muscle fibres which were treated with cryo‐protective additives (glycerol, DMSO, sucrose) or which were untreated. Freeze cleaving and etching was the basic method, with conventional plastic embedding and cryo‐ultramicrotomy as complementary techniques.Extensive crystal growth occurred during freezing in all unprotected fibres. Just below the fibre surface the crystals were numerous but small, while deeper in the fibre they were fewer but larger. The deeper within the specimen a fibre was located, the larger, in general, was the crystal size. The crystal volume density was about 55%, irrespective of crystal size. Ice recrystallization was practically absent at the temperature normally used in cryo‐sectioning (–70°C). Anti‐freeze treatment eliminated crystal growth. If the anti‐freeze agents were used in non‐toxic concentrations, however, their effect on crystal growth was very limited. ‘Dry’‐cut, freeze‐dried ultra‐thin cryosections of protected and unprotected fibres confirmed these observations, while sections obtained by ‘wet’ cryo‐cutting showed no apparent signs of crystal growth. In plastic sections of frozen and thawed fibres a previous occurrence of crystals was only slightly indicated.In interpreting the ultrastructure in ‘wet’‐cut cryo‐sections of unprotected frozen mucle fibres, the distorting effects of ice crystals through mechanical compression and alterations in sectioning conditions, must be taken into consideration. Crystal growth also strongly limits the possibilities of using ‘dry’‐cut sections of untreated frozen tissue for analytical electron microscopy; only the most superficial parts of the

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04037.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYFreeze‐fracturing of face‐centred, cubically packed, intracellular crystals of fraction 1 protein result in two distinct fracture responses of the constituent particles, according to their orientation relative to the plane of fracture. If a square‐packed plane is revealed, fracture occurs either between particles or the particles plastically deform. Conversely, if a hexagonally‐packed plane is revealed, fracture occurs either between particles or cleanly at internal planes of the particles, without any plastic deformation. It is proposed that this information may be of value in determining the arrangement of the axes of the covalently bound polypeptide protomer chains which constitute the o

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04038.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYAn environmental cell was used in the high voltage electron microscope to observe the formation of radiation damage in aluminium and dilute aluminium alloys in the presence of gas atmospheres of hydrogen, helium and air. The types of defect produced under such conditions are classified and it is shown that the characteristic of electron irradiation in the presence of a gas is the promotion of void nucleation. The implication of this observation with regard to the design of reactor materials is discussed.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04039.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYThe principal distance,D, from the centre of perspective in the SEM optical projection to the tilt axis of the specimen stage must be accurately determined before photogrammetric evaluation of stereoscopic pairs of micrographs can proceed. A precise procedure for measuringDis described in which the specimen stageXmicrometer is used to measure the width of the field scanned for a particular width of the CRT, when the specimen stage is moved along the electron beam axis by amounts measured with the stageZmicrometer. TheZmicrometer is calibrated with an external dial gauge. A plot of field width againstZextrapolated to zero gives the location of the perspective centre.In SEM photogrammetry, it is usual to leave the lens currents unchanged whilst recording the stereo‐pairs. The values ofDmeasured with a constant final lens current show that the perspective centre is located close to the final aperture in its conventional position. Previous determinations ofDforStereoscanshave used a changing lens current to keep the specimen in focus at varyingZ, and found a virtual centre several millimetres above the final aperture. The value ofDso obtained should only be used if the micrographs were recorded with dynamic or automatic focusing system

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04040.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYA specimen‐carrier for safely handling, protecting and drying minute biological specimens down to 1·0 μm in size during the various steps of the critical point drying procedure is described. Free, unattached cells or subcellular fragments can be processed without loss and without risk of unintentional air‐d

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04041.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY