bluuebunny/crossref_metadata_2025_split huggingface dataset:
Current capabilities and limitations of available stereological techniques
Authors: Weibel(Editor) Ewald R. , Fisher Colin , Gahm Joseph , Schaefer Andreas 
Published: August 2011

SUMMARYThe various methods available for stereological analysis of sectioned material are reviewed with special emphasis on a critical evaluation of their capabilities, advantages and limitations. The review deals with four main topics: (I) Comparison with structural standards; (II) Point counting methods; (III) Image analysis with the scanning microphotometer; (IV) Automatic image analysis based on television systems. It is concluded that each of these approaches has its place, and that the choice essentially depends on the properties of the material and on the nature of the problem.
The use of a low‐viscosity epoxy resin in the preparation of undecalcified bone sections for light microscopy
Authors: Xipell J. M. , Gladwin R. C. 
Published: August 2011

SUMMARYA method using the Spurr low‐viscosity epoxy resin medium for the preparation of Von Kossa impregnated undecalcified bone sections for light microscopy is described. The method gives high quality thin sections (0·6–1·0 μm) of cancellous bone and overcomes some of the difficulties experienced with other plastics. The procedure is relatively simple and is well suited for use in a routine diagnostic laboratory.
Synthesis and turnover of DNA in hepatocytes of neonatal rats
Authors: Viola‐Magni M. P. 
Published: August 2011

SUMMARYThe incorporation of 3H‐thymidine has been studied in the hepatocytes nuclei of rats during the first 3 days of life. The synthesis of DNA which occurs in 18% of nuclei after a single injection of the labelled precursors 2 h after birth, cannot be considered as premitotic since:

The hepatic cell number is constant during the first 3 days of life.
The mitotic index is less than 0·1%, 20 times lower than that expected on the basis of the labelling index and of the length of cellular cycle.
The percentage of labelled nuclei does not increase in the following 3 days.
The average number of grains per nucleus is unchanged for 18 h after the injection, a period longer than an entire cellular cycle (13 h).

This synthesis is better explained as due to an increase of DNA content per nucleus, previously described, in the hepatocytes during the first 3 days of life.After 20 h of life (18 h after label injection) a decrease of label of about 30% takes place without variation of DNA‐Feulgen dye content per nucleus. It is concluded that synthesis and turnover of DNA are present in the hepatocytes nuclei and that these processes are probably related to the functional maturation of the cells.
Studies on cell proliferation of liver epithelia in 3‐week‐old rats
Authors: Schultze Brigitte , Maurer Werner 
Published: August 2011

SUMMARYCell proliferation of liver epithelia in 3‐week‐old Wistar rats was re‐investigated. Up to a time interval of 54 h the percent labelled mitoses curve shows only one peak of labelled mitoses. From this peak a S‐phase of 8 h was derived. The results are compatible with the model of an exponentially growing population of liver cells with a growth fraction of unity and an' instantaneous' generation time of 7–1 days. The difficulties in describing the special mode of growth of liver cells in 3‐week‐old rats are discussed.The results are in complete contradiction to those from experiments of Post, Huang & Hoffman> (1963) and of Grisham (1969).
Performance and applications of the Toulouse 3 million volt electron microscope
Authors: Dupouy Gaston 
Published: August 2011

SUMMARYThis paper describes the electron microscope and gives details of its performance at an operating voltage of 3 MV.Some initial results are reported concerning: penetrating power; resolving power; studies of radiation damage, and other interactions between electrons and crystalline materials. Several observations are also described concerning biological materials (bacteria, frog skeletal muscle, filaments from mushroom spores …).Because at high voltage, radiation damage is considerably reduced, the results obtained indicate a new range of applications of high voltage electron microscopy in biological ultrastructure research.
The application of stereo‐micrography in the high voltage electron microscope to studies of cell‐wall structure and deposition
Authors: Cox Guy , Juniper Barrie 
Published: August 2011

SUMMARYStereo‐pairs taken from thick sections have proved useful in solving two problems concerned with the unusual cell walls of collenchyma. These are the three‐dimensional architecture of the cellulose microfibril skeleton of the wall and the organization of the plasmalemma and its derivatives, the paramural bodies.The basic structure of the wall is lamellate, as has been known for some decades, but the fine details of the lamellation have been the subject of controversy. A model has already been deduced on the basis of thin‐section work, but stereo‐micrography presents the opportunity of direct observational confirmation, as well as more detailed information.Wall deposition involves both the normal plasmalemma and the elaborate paramural bodies derived from it. The high voltage microscope presents the opportunity of looking at membranes in diagonal and face views, impossible in conventional ultrathin sections. In this way an increased knowledge of the structure of the membrane, as revealed in positively stained sections, has been obtained, as well as a more detailed picture of its configuration in the cell. The paramural bodies are elaborate tubular, lamellar or multivesicular bodies, continuous with the plasmalemma. Stereo‐micrography provides a much clearer view of their organization than has been possible heretofore.
The preparation and observation of thick biological sections in the high voltage electron microscope
Authors: Favard Pierre , Carasso Nina 
Published: August 2011

SUMMARYTechniques for the preparation and investigation of thick biological sections in the high voltage electron microscope (HVEM) have been studied using the Toulouse 1.5 and 3 MV microscopes.Sections several micrometres thick can be made using conventional ultra‐microtomes, but, in order to know their actual thickness, it is necessary to resection them perpendicularly to their surface after embedding them in Araldite.When successive thick sections are made with glass knives, damage may be observed on their upper surface. This can be avoided by alternating several thin sections between each thick section. Such damage is further reduced if thick sections are made using diamond knives.The maximum thickness that can be observed at a voltage of 2.5 MV is not limited by the penetrating power of the beam but by the damage suffered by irradiated Araldite. The limit is approximately 10 μm. Below 10 μm a general uniform loss in thickness is observed in irradiated areas; above 10 μm, that loss in thickness is irregular and craters are formed under the beam.Contrast can be obtained by staining tissues before or after embedding them in Araldite. The cellular structures can be uniformly stained using uranium or lead salts, or selected parts of them can be stained using colloidal tracers, Gomori's lead method, osmium or silver impregnations. The latter techniques are the more convenient as far as sections several micrometres thick are concerned.The resolving power depends on section thickness and accelerating voltage. At 2.8 MV, by using selective staining techniques, sections several micrometres thick can be investigated with a sufficient resolving power, especially with regard to understanding the spatial organization.Stereoscopic viewing allows a better interpretation by removing the inconveniences resulting from overlapping structures, but the depth of field must then be considered. Its value, for a given resolving power, taking into account the focal length of the objective lens, depends on the objective aperture: by using a 5 μm aperture one can get a depth of field of 4 μm at a resolving power of 2.0 nm and 12 μm at a resolving power of 6.0 nm, the focal length of the Toulouse 3 MV electron microscope being 10 mm. At this voltage aberrations due to diffracting phenomena are not very disturbing.
Current developments in the high voltage electron microscopy of metals and other materials
Authors: Goringe M. J. 
Published: August 2011

SUMMARYThe principal advantages of the high voltage electron microscope are first described. Examples are then quoted of various topics in the study of materials in which these advantages are being applied at present. The most obvious improvement, that of greater penetration is utilized in the study of thicker specimens, useful particularly for observation of multiphase solids, experiments in the microscope and environmental cells. The reduction in ionization damage with increasing energy allows observation of many susceptible materials, while the onset of displacement damage interferes with certain other observations. However, the study of displacement damage in nuclear materials using the very fine flux conditions in the HVEM has proved to be of great technological importance. Finally it is shown how a particular high voltage effect, the critical voltage, may be utilized.
Observation of bubble domains in the high voltage electron microscope
Authors: Jones G. A. , Grundy P. J. , Goringe M. J. 
Published: August 2011

SUMMARYA variable height holder has been constructed for the EM7 which allows the specimen to be displaced along the optic axis of the microscope. In this way a thin foil can be subjected to a large range of vertical magnetic field associated with the objective lens. So far the device has been used for the observation of magnetizing processes in thin single crystals of cobalt with the c‐axis normal to the foil. As the field on the specimen is increased by lowering it further into the lens, the usual plate domain structure is progressively converted to arrays of bubble domains. On reducing the field from saturation, bubble domains are seen to renucleate.
Combined transmission electron microscopy and X‐ray micro‐analysis of ultrathin frozen dried sections—an investigation to determine the normal elemental composition of mammalian tissue
Authors: Weavers Barry A. 
Published: August 2011

SUMMARYA variety of mammalian tissues have been prepared for electron microscopical examination by cryo‐ultramicrotomy. In conjunction with the ultrastructural investigation of the cellular and subcellular morphology of frozen sections, X‐ray micro‐analysis has been performed on various organelles in an attempt to determine their elemental composition and to monitor any variations in elemental concentrations.
Processing small delicate biological specimens for scanning electron microscopy
Authors: Marchant Harvey J. 
Published: August 2011

SUMMARYTo overcome the problems of collecting and handling delicate cells while dehydrating them for scanning electron microscopy, a method is suggested whereby cells are collected on solvent resistant Millipore filters. The schedule used for successfully processing a wide range of algae, protozoa and some other organisms is outlined as is the construction of a simple carrier to hold the filter in the critical point drying apparatus.
A design for a simple electronic exposure meter for use with an electron microscope
Authors: Hills G. J. , Garner R. T. 
Published: August 2011

SUMMARYA circuit has been developed to enable a simple yet sensitive exposure meter to be made for any electron microscope. The circuit is based around an inexpensive operational amplifier and will indicate a current range 10 −4−10 −11 A which corresponds from maximum illumination to a level of fluorescent screen illumination which is not detectable by eye. The exposure meter measures the charge on the fluorescent screen which is correlated to exposure time for photography.
Calculations and observations of the weak‐beam contrast of small lattice defects
Authors: Häussermann F. , Katerbau K. H. , Rühle M. , WILKENS M. 
Published: August 2011

SUMMARYDynamical many‐beam calculations were performed for the investigation of the diffraction contrast of small lattice defects observed in the electron microscope under weak‐beam conditions. A new computational method was developed with which the depth position zo of the defect and the thickness t of the foil were eliminated from the integration procedure of the differential equations. The contrast figures for dislocation loops which were inclined to the foil plane and for spherical inclusions were calculated for various excitation errors of the weakly excited beam and for various combinations of t and z0. The dependence of the contrast figures on z0 (‘depth oscillations’) were studied in detail. The results of the calculations are compared with experimental observations.
Evidence of dislocation dissociation in nearly stoichiometric tantalum carbide using the weak‐beam technique
Authors: Martin J. L. 
Published: August 2011

SUMMARYThe dissociation of dislocations in nearly stoichiometric tantalum carbide has been revealed by the weak‐beam technique; this is in agreement with the assumptions of a model of dislocation glide which had been derived for this compound. An order of magnitude of the partial spacing for the screw and the edge dislocation is 2·7 and 5.2 nm respectively, which leads to a stacking‐fault energy of about 170 mJ m−2 (erg cm−2).
Defocusing phase contrast effects in electron microscopy
Authors: Johnson D. J. , Crawford D. 
Published: August 2011

SUMMARYThe theory of defocusing phase contrast is presented in terms of Scherzer's (1949) ‘integrated‐ray’ and Heidenreich's (1964) ‘single‐ray’ approach to spherical aberration; contrast transfer theory in terms of the Scherzer expression is included. Fine structure in transverse sections, negative stain and carbon film is shown to be the result of defocusing phase contrast. Examples of interpretative confusion are given for various macromolecular systems and quantitative support is found for a simplified ‘rule‐of‐thumb’ approach to phase‐contrast enhancement. High‐resolution studies of carbon‐fibre lattices demonstrate contrast reversal, hence it is possible to show that a practical expression for the phase change due to spherical aberration falls between the Scherzer and the Heidenreich terms; the defocus term is also found to require some adjustment.
The application of stereo‐techniques to electron micrographs
Authors: Hudson B. 
Published: August 2011

SUMMARYIt is demonstrated that the only requisite for a true three‐dimensional image is the presence of parallax in the stereo‐pair. This parallax is introduced into electron micrographs by tilting the specimen between exposures. After deriving the usual parallax equation several examples of the use of stereo‐measurements in electron microscopy illustrate the extra information retrieved by its use.
Resolution limits in the surface scanning electron microscope
Authors: Catto C. J. D. , Smith K. C. A. 
Published: August 2011

SUMMARYAn approximate theory is developed for estimating the limiting topographical resolution of the scanning electron microscope operating under certain idealized conditions. Limitations imposed by electron beam shot noise and electron diffusion effects within the specimen are considered for the case of an instrument incorporating a field emission source and in which there is ideal collection of the secondary electron signal. The specimen is assumed to be an homogeneous, isotropic solid with the beam incident normally to its surface.It is estimated that, under these ideal conditions, the limiting resolution for a metallic specimen lies in the region of 1 nm. The possibilities of realizing a resolution of this order in a practical instrument are discussed.
Reconsideration of resolution in EM autoradiography using a biological line source
Authors: Gupta Brij L. , Moreton Roger B. , Cooper N. C. 
Published: August 2011

SUMMARYPieces of integument containing cuticle and hypodermal cells from the desert locust Schistocerca gregaria were pulse‐labelled to produce very narrow bands of radioactive chitin or resilin in the cuticle. Araldite sections of such cuticle were used as a radioactive line source to test the resolution and the possible effect of self‐absorption due to heavy metal staining of tissue‐sections in EM autoradiographs.The approximate position of the source and the half‐distance of resolution (HD) in EM autoradiographs were determined by replotting the grain‐distribution in integrated form, producing a sigmoid‐shaped curve. The values of HD, the position of the source and the total number of grains were then used to superimpose a theoretical grain‐density distribution function on the experimental grain‐distribution histograms. The results confirm the line or very narrow band nature of the radioactive chitin or resilin in the tissue‐sections used.When the source was resilin situated in the cuticle at about 1 μm from the cell‐surface, the values for HD were 130–180 nm in Ilford L4 and about 100 nm in Agfa‐Gevaert NUC 307. When the source was chitin situated just outside the cell surface, the corresponding value for HD in Ilford L4 was 85–125 nm. Possible adverse effects of electron beam damage on resolution in resilin‐containing samples are discussed.In sections with radioactive chitin at the cell surface, the total number of grains in the cell‐side of the histogram was always significantly lower than that in the cuticle‐side. This marked asymmetry in grain distribution is considered to be indicative of much greater self absorption of beta‐particles from the tritium source, in heavily stained areas of the sections.
Plastic embedding and surface erosion techniques in soft tissue scanning electron microscopy
Authors: Alexander I. G. S. , Capicchiano P. M. , Ritchie B. C. , Maloney J. E. 
Published: August 2011

SUMMARYThe maintenance and true pictorial representation of the complex cyto‐architecture of tissues is the aim of the preparatory methods for scanning electron microscopy. The procedure employed eliminates complications associated with and due to the vacuum technology necessarily employed in electron optic instruments using a scanning beam. Tissues are fixed by vascular perfusion after the administration of heparin eliminating clot formation. The infusion of Araldite in the tissues prevents the collapse and disorganization of cells due to the combined effects of dehydration, the vacuum of the scanning electron microscope and the scanning beam. The specimens are scoured with acetone and the blocks cured, this latter process ensures their permanence; the standard procedures of gold coating, stub mounting and painting the bases of specimens with a colloidal silver solution are then carried out. The method allows magnifications of the order of 10,000 diameters and an acceptable resolution of some 50 nm is obtained. Cytoarchitectural features demonstrated by the method described are borne out by transmission microscopy.
About quantitative studies on the cerebral cortex*
Authors: Bonin Gerhardt Von 
Published: August 2011

SUMMARYAmong the well established facts we can count that the cortex increases in volume against the thalamus as well as against the basal ganglia as we go from smaller to larger forms, and that the thickness of the cortex does not increase uniformly with the size of the brain. The details of the size of the thalamus and of the basal ganglia are not satisfactorily established. The values for the brains of whales and of man, which were measured by several individuals, but by the same technique, agree very well with each other.The number of cells in the cortex is not known with any degree of accuracy nor is the theoretical value of the grey cell coefficient well established. We advocate abandoning it, and replacing it with some measure of the number of synapses and/or the number of nerve fibres entering and leaving the cortex which can be established with greater accuracy.
Morphometric model, tissue sampling and test of stereologic procedures
Authors: Schroeder H. E. , Münzel‐Pedrazzoli S. 
Published: August 2011

SUMMARYStereologic point counting procedures were applied to estimate volumetric and numerical densities of tissue components residing in and forming a defined, simplified model of human marginal gingiva. This included the quantitative characterization of inflammatory cell infiltrates occurring in the epithelial as well as the connective tissue fractions of this model. The gingival tissue was harvested from defined intraoral sites of 9–15 year‐old children and processed under standardized conditions for light and electron microscopic observation. Random cross‐sections of this tissue were subjected to morphometric analysis based on a multistage sampling technique. At each sampling level, tests were performed to study (1) the suitability of different test systems, (2) the parameter variation within one and between different biopsies and (3) the comparability and reliability of the data obtained. Based on these tests, a morphometric technique was designed which resulted in an accurate estimation of the various parameters characterizing the model tissue. These parameters were the volumetric densities of the following constituents: oral epithelium, junctional epithelium and its leucocyte content, infiltrated and non‐infiltrated connective tissue, and its respective collagen fibre content. Infiltrated and non‐infiltrated connective tissue fractions were analysed for their respective volumetric and numerical densities of fibroblasts, neutrophilic granulocytes, monocytes, macrophages, small and medium‐sized lymphocytes, immunoblasts, plasma cells and mast cells. Sampling technique, test procedures and the design and results of the morphometric system are discussed.
Three‐dimensional histology; a 35 mm photographic method
Authors: Buchanan James W. , Chmielewski Stanley 
Published: August 2011

SUMMARYCommercially available photographic equipment can be used to study specimens histologically in three dimensions. Thirty‐five millimetre colour transparencies are made of serial sections at desired intervals using a photomicroscope with a rotatable stage. The series of transparencies is projected in alternate fashion using two identical projectors linked by a dissolve control. The method has proved useful in anatomic and embryologie studies and presentations as well as in evaluation of pathologic material in which initial histology revealed an abnormality that could be clarified by three‐dimensional study.
Industrial applications of analytical electron microscopy
Authors: Jacobs M. H. 
Published: August 2011

SUMMARYSome metallurgical studies carried out using a combined electron microscope — microanalyser (EMMA‐3) are described. A correction procedure is outlined for the quantitative X‐ray microanalysis of thin foils and small extracted particles. The applications discussed include (a) the examination of small crystals of carbides and spinel‐type oxides, (b) the analysis of small, single‐phase grains in splat‐quenched Al‐8%Fe, and (c) the identification of small ferrite grains within an austenite matrix by means of the convergent‐beam diffraction technique.