摘要:

SUMMARYA user evaluation has been made by electron microscopists of an X‐ray film for routine electron microscopy. The recent improvements in mammographic X‐ray films, with the attempt to reduce the patient dose required to produce a high‐resolution mammogram, have resulted in some useful films for medium‐ and high‐voltage electron microscopy. They can yield essential cytological information with a reduction of the electron fluence (exposure) applied to the specimen of more than an order of magnitude compared with conventional electron‐microscope films. Their use is indicated in situations where beam damag

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00255.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYThe problem of determining the size distribution and population density of a population of spherical particles randomly distributed throughout a transparent matrix from data obtained by transmission microscopy on parallel plane‐faced sections of known field area and thickness may be readily solved by the use of matrix algebra. The solution presented in this paper may be used to construct conversion matrices whereby the particle size distribution and the numerical density can be calculated directly from the frequency distribution of the observed diameters; the only mathematical processes necessary being multiplication and addition.Specimen conversion matrices valid for a wide range of conditions are presented in the appended table

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00256.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYAttempts were made to prepare sodium and potassium thin section standards for analytical electron microscopy by introducing, in serial concentrations, a complex between the appropriate salt and macrocyclic polyether ([15] crown‐5 for sodium and [18]crown‐6 for potassium) into epoxy resin. Of the tested salts, sodium tetraphenylborate, tetrafluoroborate and cyanide failed to produce homogeneous standards, and those standards containing sodium or potassium iodide or bromide were analytically inhomogeneous at concentrations greater than 20 meq 1−1. Only sodium thiocyanate and potassium cyanide standards were analytically homogeneous at concentrations up to 600 meq 1−1. A chlorine standard, which was analytically homogeneous at concentrations up to 1000 meq 1−1, was prepared by incorporating 1,2,4‐trichlorobenzene into an

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00257.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYPieces of mouse mid jejunum have been cleared in glycerin and examined by differential interference contrast microscopy at low powers of magnification. The position and number of crypts and villi can be determined in the same specimen using this technique. The calculated value for crypt/villus ratio 4·53 ± 0·99 (mean ± SD) is less than a previously published value obtained using indirect techniques. A revised estimate of cell renewal time, based on this newly determined value for crypt/villus ratio, is 45 h. This agrees with earlier estimates derived from entirely different methods of analysis. The general usefulness of this form of light microscopy in helping one appreciate some three‐dimensional problems in mucosal architecture is empha

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00258.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYGlutaraldehyde and glycerol are widely used in the freeze‐fracture technique as sample pretreatments before rapid freezing. However, they can both introduce relevant structural changes and influence the visualization of the fracture faces and surfaces of membranes. A comparison of the results obtained onE. colicells differently pretreated with glutaraldehyde and glycerol is presented. In particular the effect on the distribution and density of the intramembranous particles (IMP) is pointed out. Glycerol treatment at 310 K introduces an IMP redistribution, outlined by the appearance of several smooth areas on the fracture faces of the cytoplasmic membrane, which is prevented by glutaraldehyde prefixation at the same temperature. On the other hand, glutaraldehyde treatment at 310 K following glycerol incubation results in the disappearance of the smooth areas, suggesting a substantial change in the IMP distribution caused by the fixative. Cells shifted down to 277 K and treated with glycerol at this temperature before quick‐freezing, present on the convex fracture face of the cytoplasmic membrane large smooth areas resulting from a lipid transition while the smaller areas observed at 310 K are not detectable. Glutaraldehyde treatment at 277 K seems also to be responsible for a redistribution of IMP since poorly delimited large smooth areas, containing several IMP, can be observed. In this paper the results of a statistical analysis are also reported, showing that the IMP density can be strongly influenced by pretreatme

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00259.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYThe electron‐microscopical evidence for the existence of ‘nascent cellulose fibrils in green plants’ (Leppard, G.G.&Colvin, J.R.,J. Microsc.113(1978), 181) is examined critically. It is concluded that images of pre‐shadowed carbon replicas which appear to show cell wall microfibrils having a sheath enclosing a core are unavoidable technical artefacts in which the sheath consists of the replicating carbon. This interpretation is supported by the finding of similar apparent sheaths around air‐dried microfibrils which were suspended above the main plane of the substrate surface at the time of replica‐making. It is shown that the impressions of microfibrils in fractured plasma membranes have greater cross‐sectional dimensions than the microfibrils themselves as a result of the relationship between the microfibrils and the plasma membrane, and that such impressions are not evidence of ‘nascent fibrils’. Furthermore, it is argued that there is no evidence at present which supports the hypothesis that a swollen, sheathed ‘nascent fibril’ of cellulose is produced by prokaryoticAcetobacter xylinum.A light core is demonstrated in images of unshadowed replicas of microfibrils and it is proposed that radiation damage may play a rôle in the formation of this image. It is demonstrated that the coincidence of Fresnel fringes around unshadowed defocused replicas of microfibrils can also lead to the formation of an apparent core. Problems associated with obtaining measurements from replicas of cell wall microfibrils are discussed and some re

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00260.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYA technique is described whereby cells at the mitotic stage are washed off into specially designed culture tubes. Because these tubes have a small culturing area in relation to the volume of medium they contain, and the area of the original culture flask, a usable number of cell‐cycle synchronized cells are obtainable for microscopical stud

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00261.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYThe preparation and characterization of a distribution of gold balls on a thin, flat carbon film is described. The relation of the platinum carbon shadow width distribution means to a gold ball size is reported.Freeze‐etched cytochrome oxidase vesicles and gold ball calibration grids were simultaneously shadowed with platinum/carbon. The shadow width distribution of the cytochrome oxidase located in and spanning the membrane was measured. The membrane fracture face edge and cross‐fractured bilayer membrane edge were also measured.Dimensions of the cytochrome oxidase were found to be 5·8 ± 0·3 nm in diameter parallel to the membrane and 8·2 ± 0·3 nm long across the membrane. The bilayer membrane dimensions were 3·0 ± 0·3 nm for the half bilayer and 5·8 ± 0·3 nm for the cross‐fractured bilayer membrane edge thickness. The length of the cytochrome oxidase was observed to span the bilayer membrane. Previous X‐ray diffraction measurements on similar hydrated liquid crystalline artificial membranes were found to be in good agreement with the freeze‐etched results.Membrane widths from thin‐sectioned cytochrome oxidase vesicles were measured and found to be 5·8–5·9 nm in non‐post‐stained sections. Post‐staining with uranyl acetate and/or lead citrate was shown to increase this average thickness.The technique of freeze‐etching electron microscopy in conjunction with the gold ball shadow width calibration experiment has been shown to provide accurate and precise measurements of membranes and a functional intramembrane protein i

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00262.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYAccurate measurements for the stereological analysis of rough or curved surfaces are not always possible with single images from the light microscope or the scanning electron microscope (SEM). A second image recorded to form a stereo pair provides the information about the topographic nature of the surface. This paper presents two methods by which stereo pair scanning electron micrographs can be measured to give area fractions or other geometric parameters of rough surfaces.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00263.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYUranyl ions (UO22+), once bound to the phosphate moieties of phospholipid head groups, stabilize bimolecular lipid membranes (BLMs) as well as decrease the nonactin‐induced membrane conductance. UO22+bind to a phosphatidyl choline‐cholesterol (2:1, molar ratio) BLM surface with a dissociation constant of 2·3 μM and a maximum change in surface potential of 88 mV, which corresponds approximately to one uranyl ion per 31 nm2surface area. Furthermore, uranyl ions can penetrate the lipid bilayers as neutral complexes such as uranyl ac

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1980.tb00264.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY