ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03756.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

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 researc

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03757.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

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 h

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03758.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYHigh voltage electron microscopy was applied to sections of cerebellar cortex prepared by the Golgi method and embedded in epoxy resin. The silver chromate deposit in the cells consists of a fine, fibrillar meshwork upon which dense globules of various sizes may be superimposed. At the light microscope level finer images are obtained from specimens in which the fibrillar meshwork is incrusted with the fewest globules or are without incrustation. The varicosities in nerve fibres display light circular patches which represent the sites of synaptic junctions. The velamentous processes of neuroglial cells are also well demonstrated in these preparations.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03759.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYWhen rat trigeminal ganglia were osmicated for 45 h at 40°C in a 1% unbuffered aqueous solution of osmium tetroxide, only the one saccule located on the forming face of the Golgi stacks was impregnated with osmium. This staining property was therefore utilized to examine with the high voltage electron microscope the tri‐dimensional structure of the forming face of the Golgi apparatus of the small nerve cells using sections whose thickness ranged from 1 to 7 μm.In 1 μm thick sections, the osmicated ‘saccules’ actually consist of tubular polygonal networks scattered throughout the pericaryon. As the thickness of sections is progressively increased, these networks are seen to interconnect and form the so‐called ‘appareil réticulaire interne’ initially described by Golgi (1898a) in the light microscope. Stereoscopic analysis of 5–7 μm thick sections clearly demonstrates that the saccules located on the forming face of the Golgi stacks are in fact a continuous convoluted structure made up of a tubular

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03760.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

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 dis

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03761.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYAn examination of stereo‐electron micrographs taken at 1 MV in an AEI EM7 high voltage electron microscope of sections 0.5–1.0 μm thick has provided three‐dimensional information of the structural relationships in connective tissues. Sufficient contrast is obtained after block staining with uranyl acetate and with prolonged staining of the sections with lead citrate. Selective staining was observed when either the uranyl acetate or lead staining was omitted. Preliminary results indicate that there may be regions of fusion of the cisternae of the rough endoplasmic reticulum and the plasma membrane in chondrocytes that are secreting collagen. The observations also suggest that matrix vesicles in regions of calcification are formed from long cytoplasmic processes of osteoblasts by a ‘pinching off’ mechanism and that bone crystallites form within the vesicles only after the vesicles have completely separated from the surrounding cells. It is concluded that the high voltage electron microscope is capable of making a significant contribution to the understanding of the three‐dimensional structural relationships associated with specific bioche

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03762.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

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.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03763.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYRectilinear dislocation loops are observed to grow in thin foils of α‐iron during 1 MeV electron irradiation at 550°C in the beam of a high voltage electron microscope. A diffraction analysis indicates that the loops have sides parallel todirections and are pure edge withaBurgers vector. Only interstitial type loops have been identified. The geometry of the loops can be accounted for by an established model of loop nucleat

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03764.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYOne design concept for a gas cooled fast reactor fuel element utilizes directly cooled coated fuel particles. The fission product retention barrier is a pyrolytic SiC layer approximately 50 μm thick and 1 mm diameter. Knowledge of the structure of this material and its irradiation performance after high neutron doses is vital to the success of such reactors.Specimens oriented both parallel and perpendicular to the radius can be prepared from the shells by ion beam sputtering. The defect structure and preferred orientation of the coatings is being investigated. The high voltage electron beam is being utilized to measure the atomic displacement energy and to simulate fast neutron damage at temperatures relevant to reactor conditions

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03765.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY