THE FINE STRUCTURE OF CAPILLARIES AND SMALL ARTERIES

Details of capillary endothelia of the mammalian heart are described and compared with capillaries of other organs and tissues. Continuous invagination and pinching off of the plasma membrane to form small vesicles which move across the cytoplasm are suggested as constituting a means of active and selective transmission through capillary walls (12). This might be designated as cytopempsis (transmission by cell). The fine structure of the different layers in the walls of small heart arteries is demonstrated. Endothelial protrusions extend through windows of the elestica interna to make direct contact with smooth muscle plasma membranes. The elastica interna appears to vary greatly in both thickness and density, and probably restricts filtration, diffusion, and osmosis to such an extent that windows and the transport mechanisms described (cytopempsis) are necessary for the functional integrity of the smooth muscle layer. The contractile material consists of very fine, poorly oriented filaments

ELECTRON MICROSCOPE STUDY OF MAMMALIAN CARDIAC MUSCLE CELLS

The cellular theory of heart muscle is supported by a detailed description of the intercalary discs. The discs are adjacent plasma membranes separated by an interspace while the sarcolemma appears as plasma membrane, interspace plus basement membrane of the interstitium. The nucleus of the cell is closely associated with the entire cell by way of the endoplasmic reticulum. Transversely it connects the outer nuclear membrane at the level of the Z and M bands with the contractile material and the sarcolemma. Longitudinally it connects the outer nuclear membrane with the plasmalemma at the intercalated discs. The description of the spiral attachment of the endoplasmic reticulum on the outer nuclear membrane supplements earlier observations on the helicoidal structure of the heart muscle cell. Plasma membranes and endoplasmic reticulum are considered to be carriers of membrane potentials and to conduct excitation

THE BASE OF THE PROXIMAL CONVOLUTED TUBULE CELLS OF RAT KIDNEY

The three dimensional arrangement of the compartments on the base of proximal convoluted tubule cells of rat kidney is described. An extracellular basal labyrinth is found to be enclosed by these compartments. The compartments with their mitochondria and the basal labyrinth are regarded as forming a functional unit. It is supposed that this basal unit serves for excretion of reabsorbed fluid from the cell into the labyrinth and for the development of hydrostatic pressure in the labyrinth to overcome the capillary pressure and to pass the reabsorbed fluid into the blood stream

STUDIES WITH THE ELECTRON MICROSCOPE OF VIRUS-HOST RELATIONSHIPS IN EHRLICH ASCITES TUMOR CELLS : II. THE LOCALIZATION AND POSSIBLE DEVELOPMENT OF ANOPHELES A VIRUS WITHIN THE ENDOPLASMIC RETICULUM OF THE HOST CELL

Evidence is presented suggesting that anopheles A virus in the Ehrlich ascites tumor cell is harbored and propagated within the endoplasmic reticulum which in this system consists of an extensive canalicular network. The organization and differentiation of endoplasmic reticulum within the cell are described and the significance of such a location of virus is discussed

ELECTRON MICROSCOPIC AND HISTOCHEMICAL OBSERVATIONS OF MUSCLE DEGENERATION AFTER TOURNIQUET

As an experimental model for the different forms of muscle degeneration, injury caused by 2 hours' ischemia has been studied from 20 minutes to 16 hours after release of the tourniquet. Discoid degeneration developed in stretched fibers by dissolution of the I bands (Z substances and actin). The discs represented the Q bands (A-H-A). In fibers which passively maintained contraction lengths during degeneration, the Z substances were dissolved, but the continuity of the fibrils was preserved, since the filaments are continuous over all sarcomeres under these conditions. Mitochondria and the tubules of the endoplasmic reticulum swelled, ruptured, and disintegrated. Granular degeneration developed in fibers where mitochondria were abundant. Unstretched degenerating fibers with few mitochondria gave a homogeneous or hyaline appearance. The different forms of degeneration therefore were dependent on the status of stretch and the fiber type. The extent of degeneration was not a function of time after ischemia, there being both nearly normal and severely damaged fibers at 20 minutes and 16 hours after the release of tourniquets. When degeneration occurred, however, the basic alterations were the same in all fibers; there was mitochondrial and reticular swelling, dissolution of the Z substances, and finally disintegration of the contractile material. Some damage developed in the sarcolemmas and capillaries. The mitochondrial disintegration was not linked with inactivation of the succinic dehydrogenase system

QUANTITATIVE EXPERIMENTS WITH ANTIBODIES TO A SPECIFIC PRECIPITATE : III. ANTIGENIC PROPERTIES OF HORSE SERUM FRACTIONS ISOLATED BY ELECTROPHORESIS AND BY ULTRACENTRIFUGATION

1. Rabbit antisera to a Type II pneumococcus specific precipitate from horse serum were tested with fractions prepared by ultracentrifugation and electrophoresis of normal and immune horse serum. 2. In one instance a rapidly sedimenting protein from normal horse serum had nearly the same quantitative antigenic properties toward the anti-antibody rabbit serum as did the purified pneumococcus antibody solutions previously reported. In another instance a comparable fraction removed only a part of the rabbit antibody. 3. Electrophoretic γ-globulin from an immune horse serum had quantitatively the same antigenic properties as did antibody solutions prepared by salt-dissociation of specific precipitates. 4. Electrophoretic γ-globulin from normal horse serum differed in its antigenic behavior from γ-globulin containing antibody. The data are compared with the antigenic properties of acid and alkali treated pneumococcus specific polysaccharides toward antipneumococcus horse sera. An interpretation in terms of polymers is suggested. 5. The cross-reaction of goat serum γ-globulin against the anti-antibody serum is reported and the extent of the reaction compared with those of goat and horse serum albumins against a rabbit antiserum to the latter

STRUCTURE AND DEVELOPMENT OF VIRUSES OBSERVED IN THE ELECTRON MICROSCOPE : III. INFLUENZA VIRUS

Rods and spheres believed to represent viral particles were observed at the free surface of entodermal cells of the chorioallantoic membrane 6 to 44 hours after infection. Although occasional short rods revealed poorly defined internal bodies, the majority, as well as all the longer rods (filaments), exhibited no visible internal structure. The spheres presumed to lie central to the plane of section contained an inner body 20 to 22 mµ in diameter. Both forms possessed a dense, sharply defined limiting membrane 30 A thick and a diffuse external coat of lesser density. Where superimposition within the section was minimal, the viral particles were separated by a relatively constant distance. Measured to include this spacing, on the assumption that it reflected the presence of a component of the outer coat, the diameters of a majority of the rods were 50 to 60 mµ, whereas the spheres averaged 60 to 70 mµ. The rods appeared to form by a process of extrusion from the cell wall and became detached either singly or in bundles of variable length. The spheres seemed to differentiate at the cell surface and to acquire the inner body, limiting membrane, and outer coat as they migrated through the membrane of the host cell. No characteristic changes were seen in the nuclei or adjacent cytoplasm, and recognizable viral particles were never encountered in these areas of the cell. No support was obtained for the assumption that the spheres developed primarily by segmentation of the rods. It is suggested that the spherical form of the virus is the elemental infectious unit and that the filamentous form is largely or completely non-infective

SOME EFFECTS OF THE MICROTOME KNIFE AND ELECTRON BEAM ON METHACRYLATE-EMBEDDED THIN SECTIONS

A technique for the examination of specimens at low electron beam intensity has been presented. Sections micrographed with this technique showed numerous knife scratches and frequently contained bands running parallel to the knife edge. Banding with an average spacing of 0.2 µ appeared to result from periodic distortion produced by impact of the knife. At the beam intensities customarily employed, differential sublimation and probably flow of the methacrylate resulted in obliteration of the bands and all but the deepest knife scratches. In addition, changes in the size, shape, and orientation of certain structures were noted. Artifacts resulting from incineration or sublimation of tissue components fixed in formalin were illustrated, and the suggestion was made that such instability to the electron beam accounted in part for the differences observed in osmium- and formalin-fixed tissues. The deformation revealed in serial sections was discussed, and it was pointed out that shortening in the axis perpendicular to the knife edge was associated with elongation in the axis parallel to the cutting edge, the elongation usually occurring locally without change in the width of the section. It was noted that the material causing contamination of the surface of sections during examination exhibited no structure but caused progressive loss of contrast

ELECTRON MICROSCOPE STUDY OF THE DEVELOPMENT OF THE PAPILLOMA VIRUS IN THE SKIN OF THE RABBIT

Rabbit papilloma virus seems uniquely to begin its proliferation in the nucleolus of infected cells. In cells near the germinal layer of the stratum Malpighii spherical viral bodies seem to develop within a reticulum which forms out of the fine granular matrix of the nucleolus. The virus may later fill the nucleus and spread into the whole cell. The age of the cell, determined by its position in the Malpighian layer and by the extent of keratinization, can be correlated with the viral development