bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tritium‐labelled Araldite as an internal standard for quantitative autoradiography using the electron microscope
Authors: Flitney F. W. 
Published: August 2011

SUMMARYA method is described for making quantitative measurements of radioactivity from electron‐microscope autoradiographs. Autoradiographs are made from sections of tissue which contain a seam of tritium‐labelled Araldite of known radioactivity. The latter serves as an internal standard and an estimate of the tissue activity is obtained by comparing the tissue grain density with that over the standard. The method can avoid many of the problems which are commonly encountered in making quantitative measurements of tissue radioactivity.
Image formation from alloys in the field‐ion microscope
Authors: Southworth H. N. , Ralph B. 
Published: August 2011

SUMMARYPrevious studies of solid‐solution alloys with the field‐ion microscope are reviewed, and it is pointed out how their image contrast must be determined by the different response of the atomic species towards field ionization and field evaporation. The former effect, termed selective ionization, describes the relative brightness of the image points arising from the different atomic species. It is pointed out that this process is secondary to considerations of selective evaporation since the latter determines whether both species can occupy potential imaging sites in any given region of the image.Selective evaporation describes the relative fields required to evaporate the two species of atom from the specimen surface. In general the solute species will either be preferentially evaporated from the surface defined by the solvent species, or will be preferentially retained onto it. Consideration of the mechanism of selective evaporation shows that its degree may be expressed by a simple parameter calculated from known thermodynamic and atomic‐bonding data. In the later sections the model is applied to reported field‐ion data from solid‐solution alloys, excellent correlation being obtained.
Enhanced contrast in electron microscopy of unstained biological material
Authors: Johnson H. M. , Parsons D. F. 
Published: August 2011

SUMMARYElectron‐optical methods of enhancing contrast are being investigated in order to eliminate the artifacts associated with heavy‐metal contrasting procedures. This report gives a quantitative discussion of the application of the strioscopic dark‐field method to model biological objects. Beam‐stopping apertures were constructed by microwelding fine platinum wires on to platinum objective apertures. These were precisely located and centred in the back focal plane of the objective lens. Contrast was evaluated by a sensitive micro‐Faraday cage system. Bright‐field and strioscopic contrast of organic layers up to 557 nm thickness were investigated and related to the transition from single to plural scattering. The spherical‐aberration phase‐contrast contribution could be separated from the amplitude contrast in bright‐field microscopy by extrapolation to zero object thickness. Strioscopic contrast of thin layers was found to be much greater than bright field aperture contrast and shown to be non‐linear with respect to thickness in the region 0·7–10 nm. For diffraction patterns made up of a few discrete beams the resolution is high, but is considerably less for diffusely scattering and thick objects. Strioscopy may be the method of choice for obtaining contrast of unstained or weakly‐stained objects at high acceleration voltage.
Preparation of animal tissues for surface‐scanning electron microscopy
Authors: Boyde A. , Wood C. 
Published: August 2011

SUMMARYThis paper surveys common problems associated with the preparation of animal tissues so that natural or artificial surfaces may be studied in the scanning electron microscope (SEM). Problems arise because (1) we need to prepare surfaces free from extraneous solids in solution (e.g. mucus, blood, tissue fluid); (2) surfaces of simple sections generally do not reveal significant information so that other methods of ‘opening up’ internal organization must be developed; (3) we need to remove the preponderant tissue component—water—without significantly altering the remaining structure, which generally has a very low density, is fragile and is non‐conducting.In the case of natural, free surfaces to soft tissues, isolated cells or cultures the most useful approach seems to be (a) to wash with a suitable isotonic medium; (b) to fix with an aldehyde; (c) to harden with Parducz's (1967) OsO4, HgCl2 fixative.Artificial surfaces revealing details of internal organization are best prepared by dissecting and ripping aldehyde‐perfused and fixed tissue; the duration of fixation has been found to influence the location of the ripping planes in CNS. Enzymatic digestion may usefully be combined with dissection, but must be conducted before fixation.Wet tissue surface is least distorted following freeze drying from a non‐polar solvent (e.g. amyl acetate) which has substituted the tissue water. Critical‐point drying requires simple apparatus and is also generally satisfactory, but it does cause some bulk shrinkage.Specimens are best coated with a combination of carbon and gold to render them conducting: carbon because it is easily scattered and thus tends to cover very rough surfaces, and because it is tough and stabilizes the surface; gold because it is the most convenient heavy metal having high secondary‐electron emission to evaporate.Dried soft tissues have very low bulk densities, and beam‐penetration artifacts (bulk charging and edge artifacts) are therefore troublesome. These may be limited by working at as low an accelerating beam voltage as can be tolerated to achieve the required resolution. The preparation and examination of stereo‐pair micrographs is recommended as a routine because images can then be interpreted in terms of topography alone, and brightness variations of artifactual or unknown origin can be mentally excluded.
Staining of immature collagen in cattle
Authors: Schmitt O. , Dumoni B. L. , Dreyer J. H. 
Published: August 2011

SUMMARYThe staining of newborn calf tissues, using resorcin–fuchsin under different conditions, indicates that this dye is not suitable for studies of immature collagen in this species, but that a more promising stain is Van Giesons's picro–fuchsin.
An automatic sampling stage microscope for stereology
Authors: Weibel Ewald R. 
Published: August 2011

SUMMARYA new instrument is described which permits automatic sampling of microscopic fields on sections. For this purpose a motor‐driven high‐precision specimen stage was fitted to a microscope. The motors are controlled by an electronic unit to permit the following modes of operation: (a) continuous operation by a four‐position joy‐stick switch for easy and rapid scanning of the preparation; (b) single‐step operation, where the specimen is displaced in either the x‐ or the y‐direction by a preselected distance adjustable between 15 μm and 20 mm; (c) automatically repeated step operation, where the steps occur at intervals pre‐selectable between 0·5 and 34 sec; (d) scanning operation, where the specimen continuously moves along the x‐axis and is shifted to the next line at a preselected distance when the end of the sweep is reached. The details of principle and operation are presented together with a few typical examples of application.
Ultracryotomy: a technique for cutting ultrathin sections of unfixed frozen biological tissues for electron microscopy
Authors: Hodson Stuart , Marshall John 
Published: August 2011

SUMMARYAn apparatus is described which facilitates the sectioning of unfixed and unembedded biological tissues for electron microscopy. The specimen is maintained at the temperature of boiling liquid nitrogen; the knife temperature may be controlled between −50 and − 150°C. Under the worst operating conditions specimen drift with respect to the knife is about 5 nm/sec, and suggestions are made on how this drift may be further reduced. We propose to call the apparatus an ‘ultracryotome’.Electron micrographs of a variety of unfixed, unembedded and unstained tissues are shown and commented on. Some developments of experimental electron microscopy which may be expected to develop from use of the ultracryotome are listed.
Use of the X‐ray projection microscope in the examination of bone and cartilage sections
Authors: Rodriguez‐Garcia J. J. , Little K. 
Published: August 2011

SUMMARYThe conditions of use of the X‐ray projection microscope for the investigation of bone and cartilage sections have been examined. For the non‐calcified tissues an aluminium target operating at 6 kV has been found the most satisfactory. Aluminium at 15 kV and a copper target at 6 kV are also useful. The instrument is not so satisfactory as conventional microradiography for examination of fully calcified bone, but provides useful information about the softer tissues.In the X‐ray projection microscope a beam of X‐rays produced as nearly as possible from a point is used as a source of illumination, and objects to be photographed are placed between, but not in contact with, the source of X‐rays and the photographic plate. All parts of the specimen or section are equally in focus, so that details from one surface to the other are recorded on the plate with equal sharpness. Because of this depth of focus stereoscopic photographs can be taken to give additional information.The X‐ray microscope is capable of giving useful information where density differences between tissue components are of importance. The resolving power is governed by the size of the X‐ray source, while another factor that influences resolution is the X‐ray scattering factor of the tissue components. The microscope is designed to give X‐rays of different wavelength by change of target material, and of different penetrating power by altering the voltage. At the time this work started, there was insufficient information available about the conditions required for obtaining useful photographs of longitudinal and cross‐sections of bone, so that the first need was to investigate the effect of variations in the experimental method. These will be considered under three main headings: the instrument, preparation and photography of specimens, target material and voltage. An attempt will also be made to give a preliminary assessment of the areas of investigation where the instrument is likely to prove of greatest use in bone research.
Some observations on the relative dehydration rates of negative stains and biological objects
Authors: Johnson M. W. , Horne R. W. 
Published: August 2011

SUMMARYIn an attempt to explain the possible mechanism of negative staining a series of experiments are described in which the relative drying rates of two commonly used negative stains and two biological specimens were measured. Turnip yellow mosaic virus and phosphatidyl‐L‐serine were used to represent biological specimens and their dehydration rates were measured against potassium phosphotungstate or ammonium molybdate after tritiated water had been added to the solutions containing protein, lipid, negative stains or mixtures of both. From these experiments it was possible to demonstrate that the protein or lipid retains water for longer periods than the negative‐staining material. The results are in agreement with an earlier proposal that some negative stains set in a rigid ‘glass’ and thus preserve the biological structures before the latter are completely dehydrated either in air on the supporting films, or when finally dried in the vacuum of the electron microscope.
Aspects of scanning microdensitometry I. Stray light (glare)
Authors: Goldstein D. J. 
Published: August 2011

SUMMARYGlare or stray light, an important source of error in microdensitometry, is mainly due to reflections at glass‐air surfaces in the microscope objective, and much less to imperfections in other parts of the optical system. It is only slightly affected by the numerical aperture of the microscope condenser, but is closely related to the area of specimen‐free field illuminated. If Ff is the amount of glare (expressed as a fraction of the intensity of the light incident on the specimen) with a given object and area of field illuminated, and F∞ is the glare with an infinite field size or an infinitesimally small object, F∞ approximately equals FfA/(A ‐ a), where A is the area of the whole field illuminated and a is the area of the specimen itself.Glare with a given specimen and under given conditions of illumination may be taken to equal the apparent transmittance of an opaque object of the same size as the specimen to be measured, provided the opaque object is light absorbing (of low reflectance) and not too small (at least 5–10 μm diameter). The true absorbance Et of the specimen equals log [(1 ‐ F)/(Ip ‐ F)] where the intensity of the incident light is unity, and Ip is the apparent transmittance of the specimen in the presence of F glare. The true absorbance of a specimen is never less than F% higher than its apparent absorbance, in the presence of F% glare, and the error rises sharply with increasing absorbance. Apparent differences in the amount of dye taken up by nuclei of different sizes, stained by the Feulgen method, which have been reported by various workers and attributed to differences in DNA content, are of an order of magnitude which could be due to the presence of glare in the system. This factor should be allowed for in critical work.Two methods of correcting the error due to glare in measurements of integrated absorbance are described. The first method utilizes data on the area of specimen containing material with an absorbance greater than a set threshold value, as provided for example by the area‐measurement facility on the Vickers M85 integrating microdensitometer. In the second, and generally preferable method, glare is compensated for electronically in a way analogous to the offsetting of the dark‐current of the photomultiplier tube of the instrument.
A histochemical and electrophoretic study of the enzymes hydrolysing certain naphthol AS esters
Authors: Fisher A. W. F. , Bulmer D. 
Published: August 2011

SUMMARYAn investigation has been carried out into the nature of the enzymes hydrolysing two substrates, naphthol AS β‐chloropropionate and naphthol AS β‐phenyl‐propionate, which have been reported as specific for the demonstration of esterases with a proteolytic activity. Parallel histochemical and electrophoretic studies on rat liver, kidney, lung, spleen, stomach and intestine show that naphthol AS chloropropionate and phenylpropionate, used in a substrate mixture containing 20% dimethyl formamide, are hydrolysed by a large number of the non‐specific esterases which hydrolyse naphthyl acetate. The histochemical investigations show a few sites where hydrolysis of naphthol AS chloropropionate and phenylpropionate occurs without hydrolysis of naphthyl acetate, but the enzymes concerned are not present in sufficient amount to show in the zymogram patterns.
Electron microscope studies of deaminated and crosslinked collagen
Authors: Grant R. A. , Cox R. W. , Kent C. M. 
Published: August 2011

SUMMARYGlutaraldehyde‐crosslinked rat‐tail collagen, compared with native fibres, showed an increase in the size of the light bands when examined in the electron microscope using a negative‐staining technique. Collagen deaminated with nitrous acid gave similar patterns to native fibres and showed no change after treatment with glutaraldehyde. It was concluded that the increase in the size of the light bands is due to the formation of intermolecular crosslinks rather than charge neutralization of lysine amino groups.
The preparation of cross‐sections of textile materials by grinding
Authors: Lomas B. , Simmens S. C. 
Published: August 2011

SUMMARYDifficulties encountered with existing methods of obtaining cross‐sections of textile materials have been overcome by a grinding technique. This produces good, flat sections of large area and it can be used over a wide range of materials from fibres and cigarette filter tips to fabrics and metallic fibres. Little skill or experience is required and equipment costs are low.
The use of the scanning electron microscope for the study of weathered wood
Authors: Borgin Karl 
Published: August 2011

SUMMARYThe use of the scanning electron microscope for the study of the changes in the structure and ultrastructure of weathered wood was evaluated in a study of wood exposed to natural weathering for several hundred years.Stereoscan photographs taken of the surface structure of wood revealed in detail the mechanism of the structural breakdown, which could not be found by using the light microscope or the conventional transmission electron microscope.The gradual and very slow deterioration and ultimate destruction of the middle lamella, the various layers of the cell wall and the cohesive strength of wood tissue as well as the wood fibres are illustrated by a serious of photographs.Since no preparative technique can be used which would interfere with the surface of the weathered wood and due to the deep three‐dimensional change in the structure, the scanning electron microscope was found to be the ideal instrument for the study of the structure of weathered wood at both high and low magnification with excellent resolution of detail.
A new technique for specimen manipulation in the scanning electron microscope
Authors: Bywater N. E. , Buckley T. 
Published: August 2011

SUMMARYBy the use of suitable DC micromotors mounted on the specimen stage of the Cambridge Scanning Electron Microscope (SEM), extra degrees of freedom may be imparted to the specimen, thus enabling a more thorough examination of a surface to be carried out. The properties that make an electric motor suitable for use inside the vacuum specimen chamber are discussed. After showing the way in which DC motors have successfully solved two problems in the fibre field, some further applications are proposed.
The statistical analysis of autoradiographs: I. Grain count distributions over uniformly labelled sources
Authors: England J. M. , Rogers A. W. 
Published: August 2011

SUMMARYAutoradiographs have been prepared of sections of tritiated poly‐n‐butyl methacrylate (‘tritiated polymer’). Repeated visual grain counts over the sections showed good agreement with predictions from a Poisson distribution, as did similar counts of background from around the sections. Photometric measurements of grain density from the same material could also be analysed in terms of a Poisson distribution. The processes of autoradiography and grain counting whether visual or photometric, do not necessarily introduce any added variance to that attributable to the randomness of radioactive disintegration.
Field‐ion images of dilute solid solutions
Authors: Ryan H. F. , Suiter J. 
Published: August 2011

SUMMARYVacant‐site contrast observed in the field‐ion images of Pt‐Rh, Pt‐Au and Au‐Pd alloys is interpreted in terms of preferential evaporation of the solute atoms. Preferential retention of the solute atoms was observed in a Au‐Pt alloy. These observations conflict with predictions based on a theory of image formation proposed by Southworth & Ralph (1969).
Materials for teaching microscopy in the sixth form*
Authors: Gliddon Richard 
Published: August 2011

SUMMARYRecent events in scientific and educational research demand that we examine critically the role of the microscope in sixth‐form biology. The advent of the electron microscope has removed the light microscope from its position as the ultimate in structural studies. The many new sixth‐form syllabuses have caused us to change from almost purely descriptive biology, with a strong emphasis on anatomy and histology, to a more balanced approach with time devoted to experimental work in such fields as physiology, biochemistry, ecology, embryology and genetics. The microscope is no longer the most expensive piece of equipment in a sixth‐form laboratory, but it is still the most versatile and valuable. It is still the best instrument we have for observing events in living materials.With some careful thought and planning the light microscope can be effectively used in a good deal of experimental work with living or freshly prepared materials. It also enables us to miniaturize such topics as ecology and behaviour which might otherwise be neglected in urban areas. A functional approach to histology has always been the real aim of the histologist and some staining techniques help us to achieve that aim.Quite a number of practical experiments in physiology, biochemistry and genetics also depend on use of the microscope. Behaviour, ecology and experimental embryology are all fields where materials can be successfully studied under the microscope. Some suggestions are made for suitable materials for the microscope in these experimental fields.
Preparation and mechanical requirements for freeze‐etching thick‐walled plant tissues*
Authors: Robards A. W. , Parish G. R. 
Published: August 2011

SUMMARYThe freeze‐etching technique is useful in studying cells from higher plant tissues even when thick cell walls are present. However, such cells require special consideration both in preparation for the freeze‐etching process as well as during fracturing and subsequent stages. Modifications to the technique and to the apparatus are described which make it possible to freeze‐etch thick‐walled plant tissues more successfully than by employing other methods.
A rapid method for the visual determination of size distribution of spheres from the size distribution of their sections*
Authors: Hennig August , Elias Hans 
Published: August 2011

SUMMARYThe difficulty of calculating size distributions of spheres in masses from the size distributions of sectional circles is overcome by providing standard pairs of curves representing most imaginable particle‐size distributions which might occur in nature. An observer needs only to match the histogram representing his own observations with one of the new curves to obtain immediately the size distribution of spheroid particles in his material.
The synthesis of the immobilization antigens in Paramecium aurelia: in situ localization of immobilization antigen using fluorescein‐or ferritin‐conjugated antibodies
Authors: Sinden R. E. 
Published: August 2011

SUMMARYA technique is described for the preparation of frozen sections of a cell suspension of Paramecium, in an aqueous medium, that produces negligible ultra‐structural distortion. Incubation of osmium tetroxide‐fixed sections with fluorescein or ferritin‐conjugated globulins has revealed two extensive non‐immune reactions: namely, globulin‐tissue adsorption, and globulin‐globulin adsorption. The distribution of a group of antigenic proteins‐the immobilization antigens‐in P. aurelia was investigated using both fluorescein‐and ferritin‐conjugated globulins prepared from the sera of rabbits immunized with purified immobilization antigen. The majority of the immobilization antigen is located on the outer surface of the pellicle, but trace quantities are detected in an unresolved cytoplasmic fraction.
Cytochemical localization of ATP‐ase activity in plant root cells*
Authors: Hall J. L. 
Published: August 2011

SUMMARYATP‐ase activity in root‐tip cells of Zea mays has been localized by using a lead phosphate precipitation procedure. Activity is associated with the plasmalemma, nucleus, mitochondria, Golgi bodies, vacuoles and endoplasmic reticulum al though the relativeactivities vary in different regions of the root. The localization of surface ATP‐ase is compared with that of surface β‐glycerophosphatase and the results discussed in relation to the possible role of ATP‐ase in ion transport.