摘要:

SUMMARYThe Foucault in‐focus method for viewing magnetic domains in a conventional electron microscope has been modified. The main feature of our modification is to introduce an aperture below the intermediate lens and to use it for stopping out one part of the split central spot instead of the objective aperture. This arrangement substantially reduces the axial astigmatism due to the objective aperture and makes it possible to reach the point resolution 5–6 nm in both light and dark domains. The image resolution is limited by the small image magnification achieved using the three‐stage optical system of a Tesla BS 413 micro

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03949.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYA procedure for the freeze‐substitution fixation of spermatozoa has been developed. Physical fixation of the motile cells is effected very rapidly by immersing the sperm in Freon‐22 at −146°C. Chemical fixation, with glutaraldehyde, is then imposed on the immobilized sperm after substitution of the ice matrix at −50°C. The substitution is achieved with the solvent ethylene glycol in the manner described by Pease (1967). (Subsidiary experiments confirm that substitution of ice does occur at −50°C and that chemical fixation by glutaraldehyde occurs at temperatures at least as low as −20°C.) The spermatozoa are then embedded in Epon and examined as thin sections. Other techniques—substitution in acetone containing osmium tetroxide, the inclusion of formaldehyde with ethylene glycol as a chemical fixative, and the inclusion of agar in the diluent used to suspend the spermatozoa—have been tried but were unsatisfactory.Freezing stops the movement very rapidly and, as little subsequent disturbance occurs, it should be possible to preserve transient changes in the fine structure of the flagellum which might be related to a mechanism for the generation of bends. The observations in this paper are confined to the behaviour of the proximal part of the midpiece of the rat spermatozoon. It is demonstrated that bending of this part of the flagellum is restricted, to a remarkable degree, to one plane, the plane in which the sperm nucleus is flattened. This plane is almost exactly perpendicular to the plane containing the two central tubules of the axoneme. It has been confirmed that the axonemal complex has a straight course through the midpiece during those beats of the flagellum which are not accompanied by rotation of the entire cell. Lastly, it appears that the nine dense fibres do not undergo transient displacements as

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03950.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYA stereological grid method has been evolved for scanning electron microscopy using a self‐generated superimposed grid which compensates for the non‐linearity of the CRT image. The method was applied to determine the volume proportion of lacunae in monkey humerus cortical bone. Flat cut specimens of bone were prepared and photographed with a superimposed grid, and the number of lacunae on intersections of the grid were counted and compared with the total number of intersections on bone matrix. The lacunar volume proportion was 1.06% ± 0

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03951.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYEfficient application of point counting stereological methods in quantitative microscopy in biology and materials science depends on the availability of powerful and rapid counting and computing facilities. An on‐line computer system is described which is easily programmed without knowledge of a special programming language to perform counting, computation of parameters, and statistical tests automatically. By means of a master program, provided with the system, specific user's programs are compiled on a teletype in conversation with the computer by following simple instructions. The program is distinguished by great flexibility; it provides for statistical tests on the reliability of the sample analysed at any time during analysis. The final results are printed in tabular form as means and standard errors of the mea

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03952.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe macroscopic examination of irradiated reactor materials presents special problems in handling due to the necessity of shielding the instrument from the worker with a thick lead wall. The lack of availability of a suitable instrument has prompted the design of a special inverted stage macroscope equipped for remote operation. As the size of lens prevents turret mounting, a commercial 35 mm camera telephoto lens has been adapted in a special focusing mount. This permits the illuminator and stage assembly to be made non‐adjustable, simplifying the problems of remote working. An electronic drive is fitted to each stage movement, both of which are provided with remote position indicator

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03953.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYAn annoying phenomenon in many low power electron microscope negatives is a centrally located overexposed spot. It is shown that its occurrence is associated with the use of thin‐foil objective apertures, and that the spot most probably is produced by electrons permeating the thin‐foil material. The overexposed spot can be avoided either by using a concentrated nearly focused illuminating beam, in practical terms by using a short exposure time, or by using a thick, disc‐shaped objective ape

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03954.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe resolution of structurally significant detail in electron micrographs of organic polymers is limited by damage to the specimen during electron irradiation. The factors affecting the kinetics of the degradation of characteristic high angle reflections in the electron diffraction patterns of Cellulose I and II have been studied in an attempt to determine quantitatively the conditions under which meaningful high resolution micrographs may be recorded.In Cellulose I it was established that the decay of the 002 reflection during irradiation (in the range 0.6‐6.0 Am−2) is independent of dose‐rate. Moreover the meridional 040 and equatorial 002 reflections were found to decay at different rates. This latter finding indicates the importance of selecting the appropriate conditions for imaging a particular structural repeat in a specimen. Perhaps the most significant conclusion arising from this work is that specimen cooling in conjunction with low‐beam densities may be used to considerable advantage in obtainingmeaningfulhigher resolution images than hitherto possible in beam‐sensitive

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03955.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYFreeze‐drying is a useful way to maintain the three‐dimensional morphology of biological materials for electron microscopy. The process is achieved simply by utilizing a commercially available thermoelectric unit within a standard vacuum evapora

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03956.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYQuantitative measurements on electron micrographs with less than 10% error require precise calibration of all lenses contributing to the final image magnification. Calibration of the magnification to approximately 1.5% is easily attained by using simple statistical methods and a digital display milliampere meter capable of measuring the objective, intermediate and projector lens currents independently. The method detailed, readily adaptable to other electron microscopes, requires the projector lens current be held constant, with the magnification determined by varying the intermediate lens current and corrections made on the basis of calibrated objective lens current effect. The errors of magnification, approximately 1.5%, are the same range as the test grid variation which appears to be the limiting factor. Even with this limitation, magnifications have been determined reproducible to within less than 0.2% in daily use over a 6 month period.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03957.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe standard ‘Stereoscan’ specimen stub has been modified to permit palynological acid‐maceration techniques to be performed under aseptic conditions. It is hoped that this adaptation will also be of use where contaminant‐free pure culture preparations are required, where delicate specimens are being treated, or where it is desirable to examine the precipitated products of chemical re

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb03958.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY