bluuebunny/crossref_metadata_2025 huggingface dataset:
ELECTRON MICROSCOPIC STUDIES OF MITOSIS IN AMEBAE
Authors: Roth L. E. , Daniels E. W.
Published: May 2004

Dividing nuclei from the giant ameba Pelomyxa carolinensis were fixed in osmium tetroxide solutions buffered with veronal acetate to pH 8.0. If divalent cations (0.002 M calcium, magnesium, or strontium as chlorides) were added to the fixation solution, fibrils that are 14 mµ in diameter and have a dense cortex are observed in the spindle. If the divalent ions were omitted, oriented particles of smaller size are present and fibrils are not obvious. The stages of mitosis were observed and spindle components compared. Fibrils fixed in the presence of calcium ions are not so well defined in early metaphase as later, but otherwise have the same diameter in the late metaphase, anaphase, and early telophase. Fibrils are surrounded by clouds of fine material except in early telophase, when they are formed into tight bundles lying in the cytoplasm unattached to nuclei. Metaphase and anaphase fibrils fixed without calcium ions are less well defined and are not observably different from each other. The observations are consistent with the concept that spindle fibrils are composed of polymerized, oriented protein molecules that are in equilibrium with and bathed in non-oriented molecules of the same protein. Partially formed spindle fibrils and ribosome-like particles were observed in the mixoplasm when the nuclear envelope had only small discontinuities. Remnants of the envelope are visible throughout division and are probably incorporated into the new envelope in the telophase. Ribosome-like particles are numerous in the metaphase and anaphase spindle but are not seen in the telophase nucleus, once the envelope is reestablished, or in the interphase nucleus.
THE STRUCTURE OF THE LIQUID-CRYSTALLINE PHASES OF LIPID-WATER SYSTEMS
Authors: Luzzati V. , Husson F.
Published: May 2004

Some simple lipid-water systems have been studied by x-ray scattering techniques, as a function of lipid concentration and temperature. Several liquid-crystalline phases have been found, and their structure has been determined: only one of these is lamellar. In all these phases the hydrocarbon part of the lipid molecules has a disordered, liquid-like structure. One biological phospholipid, a human brain extract, has been studied by the same technique, and two liquid-crystalline phases have been found: a lamellar phase, built up by an ordered sequence of lipid and water planar sheets, and a hexagonal phase, which is a hexagonal array of circular cylinders, each cylinder being a thin water channel covered by the hydrophilic groups of the lipid molecules, the hydrocarbon chains filling the gap between the cylinders. The interpretation of the electron microscope observations of the structure of lipoprotein membranes is discussed, and some possible biological implications are suggested.
INTRACELLULAR LOCALIZATION OF ENZYMES IN SPLEEN
Authors: Eichel Herbert J. , Roth Jay S.
Published: May 2004

Some properties of rat spleen ribonuclease have been studied, and the intracellular distribution of the enzyme and ribonucleic acid have been presented. Spleen ribonuclease exhibits maximal activity at pH 5.8, and although there is some evidence for the presence of an enzyme with an optimum at pH 7.0, it is not conclusive. The enzyme is concentrated primarily in the mitochondrial fraction, but significant quantities occur in the supernatant fluid. The latter contains ribonuclease inhibitor similar to that found in liver. The effects of whole body x-irradiation, magnesium ion, substrate concentration, type of buffer, presence of p-chloromercuriphenylsulfonic acid, deoxycholate, and Triton X-100 on ribonuclease activity are examined.
THE DEGENERATIVE CHANGES IN PANCREATIC ACINAR CELLS CAUSED BY DL-ETHIONINE
Authors: Herman Lawrence , Fitzgerald Patrick J.
Published: May 2004

Degeneration of pancreatic acinar cells in rats injected with ethionine was studied by electron microscopy. The most conspicuous morphologic lesions occurred in the ergastoplasm. There was a widening of the endoplasmic reticulum, a decrease in number of membrane-associated ribosomes, and a development of fine and coarse vacuoles containing agranular disoriented membranes. Cytoplasmic ribosomes unassociated with membranes were less numerous. Nuclear changes consisted of a coarsening and clumping of the nuclear chromatin, chromatin margination, and increased osmiophilia and vacuolation of the nucleolus. Eight to ten days after the beginning of ethionine injections, changes in zymogen granules, mitochondria, and the Golgi apparatus appeared, but only after extensive damage to the acinar cell. The effects were consistent with ethionine's known interference with protein metabolism but also suggest disturbance in ribonucleic acid metabolism. The ergastoplasmic changes after ethionine were similar in some respects to the early lesions produced in liver parenchymal cells by fasting, to the changes occurring in animals on protein-free diets, or to some of the liver changes produced by azo dye carcinogens. The ribosomal and ergastoplasmic changes represent early morphologic expressions of the biochemical effect of ethionine.
CHANGES IN PANCREATIC ACINAR CELLS DURING PROTEIN DEPRIVATION
Authors: Weisblum Bernard , Herman Lawrence , Fitzgerald Patrick J.
Published: May 2004

After 10 days of a protein-free diet the acinar cells of the rat pancreas showed a coarsening of nuclear matrix, depletion of zymogen granules, some loss of ribosomes, and a widening of the spaces between ergastoplasmic membranes. In addition, there could be found, but rarely, a lesion of the ergastoplasm consisting of vacuoles of agranular, disoriented membranes, which was similar to a lesion produced by ethionine. Thereafter, a return toward normal structure occurred which was characterized by beginning increase in the size of the Golgi apparatus at 12 days, appearance of zymogen granules at 18 days, and a relatively normal appearing but smaller cell at 28 days. After 10 to 12 days of protein deprivation a reversal of many of the morphologic effects of protein deprivation was accompanied by a return toward normal of some pancreatic enzyme activities. Possibly this spontaneous return toward normal levels represented a raiding of protein stores, or it may have been an adaptive phenomenon.
THE FINE STRUCTURE OF ACOUSTIC GANGLIA IN THE RAT
Authors: Rosenbluth Jack
Published: May 2004

Nerve cell bodies in the spiral and vestibular ganglia of the adult rat are surrounded by thin (about ten lamellae) myelin sheaths which differ in several respects from typical axonal myelin. In some instances lamellae surrounding perikarya appear as typical major dense lines, and in others as thin Schwann cell sheets in which cytoplasm persists. Discontinuities and irregularities appear in the structure of perikaryal myelin. Lamellae may terminate anywhere within the sheaths; they may bifurcate; they may reverse their direction; or they may merge with each other. The number of lamellae varies from one part of a sheath to another. In addition, the myelin of a single perikaryal sheath may receive contributions from more than one Schwann cell, which overlap and interleave with each other. The ganglion cells are of two types: those which are densely packed with the usual cytoplasmic organelles but have few neurofilaments (granular neurons), and those which exhibit large areas containing few organelles but have a high concentration of neurofilaments (filamented neurons). The latter cell type is ensheathed by myelin which is generally more compact that that surrounding the former. The formation and the physiologic significance of perikaryal myelin are discussed.
STUDIES ON THE CORNEA
Authors: Kaye Gordon I. , Pappas George D.
Published: May 2004

Physiological studies have demonstrated that ions, as well as large molecules such as hemoglobin or fluorescein, can diffuse across and within the cornea. Most of the substrates for corneal metabolism are obtained from aqueous humor filling the anterior chamber. In order to receive its nutrients and in order to maintain its normal conditions of hydration, the avascular cornea must transport relatively large amounts of solute and solvent across the cellular layers which cover this structure. It has been suggested in the past that there may be a morphological basis for the transport of large amounts of solvents and solutes by cells by the mechanism of pinocytosis. The use of electron-opaque markers to study fluid movements at the electron microscope magnification level was described by Wissig (29). The present study describes the fine structure of the normal rabbit cornea and the pathways of transport of colloidal particles by the cornea in vivo. Rabbit corneas were exposed in vivo to suspensions of saccharated iron oxide, thorium dioxide, or ferritin by injection of the material into the anterior chamber. In other experiments thorium dioxide or saccharated iron oxide was injected into the corneal stroma, producing a small bleb. Particles presented at the aqueous humor surface of the rabbit corneal endothelium are first attached to the cell surface and then pinocytosed. It appears that the particles are carried around the terminal bar by an intracellular pathway involving the pinocytosis of the particles and their subsequent transport in vesicles to the lateral cell margin basal to the terminal bar. Particles introduced at the basal surface of the endothelium (via blebs in the corneal stroma) are apparently carried through the endothelial cells in membrane-bounded vesicles without appearing in the intercellular space. There appears to be free diffusion of these particles through Descemet's membrane and the corneal stroma. The stromal cells take up large quantities of the particles when blebs are injected into the stroma.
STUDIES ON THE CORNEA
Authors: Kaye Gordon I. , Pappas George D. , Donn Anthony , Mallett Nancy
Published: May 2004

In vitro studies of the transport of colloidal particles by the cornea were carried out on intact corneas of adult rabbits in a chamber described by Donn, Maurice, and Mills (2) in which the epithelial or the endothelial surface of the cornea was exposed to thorium dioxide or saccharated iron oxide under various conditions. These studies confirmed the results of previous work in vivo and allowed modification of the experimental conditions. Particles are pinocytosed at the apical surface of the corneal endothelium and carried around the terminal bar in membrane-bounded vesicles. Basal to the terminal bar these vesicles fuse with the lateral cell margin and their contents are released into the intercellular space, in which they appear to be carried by a one-way flow down to Descemet's membrane and the corneal stroma. Indications that the endothelial transport is an active process are presented by the different pathways of transport into or out of the corneal stroma, as well as by the approximately 70 per cent reduction in transport activity at low temperatures.
OBSERVATIONS ON THE MODE OF RELEASE OF HERPES VIRUS FROM INFECTED HELA CELLS
Authors: Epstein M. A.
Published: May 2004

The development of a well adapted strain of herpes virus has been studied in HeLa cells using thin sectioning techniques for electron microscopy. Particular attention was directed to events in the cytoplasm and certain new features were observed. Profuse immature particles with a nucleoid and single limiting membrane were present in the nuclei of infected cells, often in crystalline array; morphologically indistinguishable immature particles were also found very frequently in the cytoplasm. Cells with such particles were intact and well preserved, and contained smooth vacuoles apparently derived from the Golgi component of the endoplasmic reticulum. The cytoplasmic particles escaped from the cells by bulging out as buds through the cell membrane or through that of the cytoplasmic vacuoles until they were attached only by a pedicle and then became free. During this process the particles were gradually enclosed by the membrane through which they passed and carried a coat of it with them as they matured. After permanganate fixation the triple-layered structure of the cell membrane and vacuolar membranes was evident and was identical with that of the outer coat of the mature virus. These findings are discussed both in relation to different types of virus structure and to function in the endoplasmic reticulum and cell membrane.
STUDIES ON CARTILAGE
Authors: Sheldon H. , Kimball F. B.
Published: May 2004

Electron microscopic observations on chondrocytes from rabbit ear cartilage 72 hours after papain has been given intravenously show that many vacuoles in the Golgi apparatus contain a material with a speckled appearance. Some Golgi vacuoles also contain a material with a banded pattern which can be identified as a collagen. The significance of this observation is discussed.
THE FINE STRUCTURE OF THE MID-BODY OF THE RAT ERYTHROBLAST
Authors: Buck Robert C. , Tisdale James M.
Published: May 2004

The development of the mid-body has been studied in mitotic erythroblasts of the rat bone marrow by means of thin sections examined with the electron microscope. A differentiated region on the continuous spindle fibers, consisting of a localized increase in density, is observed at the equatorial plane. The mid-body seems to develop by the aggregation of such denser lengths of spindle fiber. Its appearance precedes that of the cleavage furrow. A plate-like arrangement of fibrillary material lies transversely across the telophase intercellular bridge. Later, this material becomes amorphous and assumes the form of a dense ring closely applied to a ridge in the plasma membrane encircling the middle of the bridge. Although the mid-body forms in association with the spindle fibers, it is a structurally distinct part, and the changes which it undergoes are not shared by the rest of the bundle of continuous fibers.
ORIENTATION AND LOCUS OF TROPIC PHOTORECEPTOR MOLECULES IN SPORES OF BOTRYTIS AND OSMUNDA
Authors: Jaffe Lionel , Etzold Helmut
Published: May 2004

Study of the tropic responses of Botrytis cinerea and Osmunda cinnamomea spores to blue light shows the photoreceptor molecules to be highly dichroic and oriented: in Botrytis their axes of maximum absorption lie perpendicular to the nearby cell surface; in Osmunda, parallel. The chief evidence lies in a comparison of their responses to plane polarized light—both germinate parallel to the vibration planes (defined by the axis of vibration of the electric vector and the axis of light propagation)—with those to partial illumination with unpolarized light: Botrytis grows from its brighter part; Osmunda, from its darker. The degree of orientation produced by polarized light corresponds, at high intensities, to that produced by the imposition of such large (about 100 per cent) intensity differences across a cell as to preclude all alternatives to oriented dichroic receptors. The photoreceptors of the Botrytis spore lie within the cell wall's inner half. The chief evidence lies in the component of its tropic responses to polarized light within the vibration plane: germination peaks about 10° off the vibration axis. This deviation arises from focusing which is effective only in the wall's inner half. At high intensities, anomalies appear in Botrytis which are interpreted as "centering," i.e., a tendency toward growth from the center of two or more equally illuminated points of a cell rather than from one of them.
ELECTRON MICROSCOPIC OBSERVATION OF SPECIMENS UNDER CONTROLLED GAS PRESSURE
Authors: Heide Hans Gunther
Published: May 2004

A technique for encasing specimens in a thin gas layer during their observation in the Siemens Elmiskop I is described. All gases can be employed at pressures up to one atmosphere. Destruction of specimens can occur in the beam; all organic specimens are particularly liable to decompose. The conditions under which this can be avoided are given. A useful application of the technique allows one to prevent specimens from drying out, as they normally do in vacuum. A further application uses the controlled removal of carbon for thinning organic layers and for selective etching of organic materials.
FUNCTIONAL EVIDENCE FOR THE EXISTENCE OF A THIRD CELL TYPE IN THE RENAL GLOMERULUS
Authors: Farquhar Marilyn G. , Palade George E.
Published: May 2004

Two types of cells can be recognized on the luminal side of the glomerular basement membrane: the superficial endothelial cells which directly line the lumen and are comparable to endothelia lining the capillaries of other tissues, and the deep cells, ordinarily not in contact with the lumen, which are distinguished by their long cytoplasmic arms extending for some distance in several directions along the capillary wall, numerous spinous processes, and occasional intraluminal pseudopodia. Experiments carried out with electron-opaque tracers indicated that a functional distinction, based on extent of phagocytosis, can be made between the superficial and deep cells, thus supporting the existence of a distinctive "third" cell (in addition to endothelium and epithelium) in the renal glomerulus.

Ferritin, colloidal gold, or thorotrast was administered intravenously to normal and, in the case of ferritin, to nephrotic rats. Kidney tissue was fixed at selected intervals from 1 hour to 10 days after the injection and studied by electron microscopy. Within 1 to 4 hours after tracer administration, the particles which did not traverse the glomerular capillary wall gradually accumulated in the less compact, inner strata of the basement membrane and the large spongy areas of axial regions. After 1 day the concentration of circulating tracer declined and the peripheral areas of the capillaries became relatively free of particles while large accumulations developed in the axial regions. During this period increasing quantities of ferritin were taken up by the deep cells and were found within large and small sized invaginations of their cell membrane or concentrated within cytoplasmic vesicles, vacuoles, multivesicular and dense bodies. At the same time the deep cells showed increased numbers of intraluminal pseudopodia. Within 2 to 4 days the deposits in the spongy areas were cleared and concomitantly increased quantities of tracer appeared in the deep cells within dense cytoplasmic bodies, some of which were more compact than before. When ferritin was given to nephrotic animals the sequence of events was generally the same except that the ferritin deposits at any given period were more massive, their incorporation into the deep cells occurred primarily by means of large pockets 1 to 2 µ in diameter and their clearance from the spongy areas was slower. In normal as well as in nephrotic animals, the phagocytic activity of the superficial endothelium was negligible when compared to that of the deep cells.
THE GRANA OF STARCH-FREE CHLOROPLASTS OF NICOTIANA RUSTICA
Authors: Weier T. Elliot , Thomson William W.
Published: May 2004

The grana of chloroplasts of starch-free leaves of Nicotiana rustica are described in detail. Leaf sections were fixed in 2.5 per cent KMnO4 and embedded in mixtures of butyl and ethyl methacrylate. Chain length of the polymer was modified by use of a transfer agent. The grana are composed of compartments consisting of electron-scattering partitions and electron-transparent loculi. Compartments are not open to the stroma so that the grana are distinct subplastid organelles. Adjacent grana are connected by an anastomosing fretwork system composed of flexuous channels bordered by electron-scattering membranes. Ten different kinds of granum margins are described. These marginal variations depend upon grana-fretwork connections and internal marginal connections between adjacent loculi. A study of serial sections suggests, at least in some plastids, the occurrence of a possible orderly spiral arrangement of compartment-fretwork connections. Adjacent grana may have common compartments. Grana may branch. Variations in shape may depend upon the angle the section bears to the axis of the cylinder. This should also influence the relative thickness and sharpness of the partitions. Since all shapes and variations in partition thickness and sharpness cannot be accounted for on the basis of the orientation of the grana, such variations probably occur naturally. Grana vary in size, ranging from those few which have a single partition to those having 50 or more compartments which extend completely through the width of a plastid. Relationships between grana of different sizes and between compartments and frets indicate the possibility of growth of grana from union or extension of compartments and formation of compartments from the union of frets.
CYTOCHEMICAL STUDY ON THE PANCREAS OF THE GUINEA PIG
Authors: Siekevitz Philip , Palade George E.
Published: May 2004

Pancreatic ribosomes (guinea pig) aggregate and lose upon treatment with polyamines, particularly spermine, their bound secretory enzymes. Spermine, at 0.5 mM, for example, causes the release of about 85 per cent of the chymotrypsinogen and RNase, and from 85 to 100 per cent of the ribosomal amylase. At the same time, the particles lose about 10 per cent of their RNA, 7 to 24 per cent of their total protein, and from 75 to 100 per cent of their Mg++. Observations with the electron microscope confirm the heavy agglutinating of the ribosomes but otherwise show little change in the structure of the particles. Using radioactive spermine it was found that, concomitant with the loss of bound enzymes and Mg++ from the ribosomes, spermine became bound to the particle. The extent of binding ranged from 0.29 to 1.49 µmoles per 10µmoles RNA-P. The bound radioactive spermine can be removed by subsequent treatment of the ribosomes with GTP, ATP, or P-P, which treatment also removes most of the RNA of the particles, leaving behind ribosomes with a much lower RNA/protein ratio. From this evidence it was inferred that spermine, in releasing the Mg++ of the particle, becomes salt-linked to the free phosphate hydroxyl groups of the RNA. Freshly isolated pancreatic and hepatic ribosomes contain very little spermine, about 0.1 to 0.2 µmoles polyamine/10 µmoles RNA-P. The results are discussed in terms of the linkages between the structural protein, the bound secretory enzymes, and the RNA of the ribosomes.
ELECTRON MICROSCOPY OF LYSOSOME-RICH FRACTIONS FROM RAT THYMUS ISOLATED BY DENSITY-GRADIENT CENTRIFUGATION BEFORE AND AFTER WHOLE-BODY X-IRRADIATION
Authors: Rahman Y. E.
Published: May 2004

Fractions from rat thymuses were isolated by sucrose density-gradient centrifugation, before and after 1000 r whole-body x-irradiation, and examined by electron microscopy. Cytochrome oxidase and acid phosphatase activities of these fractions were tested as well. Electron-opaque bodies with diameters ranging from 0.10 to 0.35 µ, with a mean of 0.25 µ, were found in fractions having high acid phosphatase activity, while the fractions rich in cytochrome oxidase consisted mostly of mitochondria. After irradiation, there was an increased ratio of dense bodies to mitochondria. These particles are considered to be lysosomes similar to those identified in other rat tissues. Their relationship to the mitochondria is discussed.
ULTRASTRUCTURE OF DNA-CONTAINING AREAS IN THE CHLOROPLAST OF CHLAMYDOMONAS
Authors: Ris Hans , Plaut Walter
Published: May 2004

The chloroplast of Chlamydomonas moewusii was examined by electron microscopic and cytochemical methods for the possible presence of DNA. Both the Feulgen reaction and acridine orange indicated the presence within the chloroplast of one or more irregularly shaped DNA-containing bodies generally in the vicinity of the pyrenoid. Electron micrographs revealed 25 A microfibrils in these areas which correspond to DNA macromolecules with respect to their location, morphology, and sensitivity to deoxyribonuclease digestion. The possibility that this material is the genetic system of the chloroplast and the hypothesis that the chloroplast represents an evolved endosymbiont are discussed.
A NEW EPOXY EMBEDMENT FOR ELECTRON MICROSCOPY
Authors: Freeman James A. , Spurlock Ben O.
Published: May 2004

A new epoxy embedding mixture has been developed utilizing Maraglas 655 and Cardolite NC-513 with benzyldimethylamine (BDMA) as a curing agent. This epoxy mixture permits cellular preservation comparable to that obtained with Epon 812, ease of preparation of tissues, a wide range of miscibility, low viscosity, and, most important, ease of sectioning on a Porter-Blum microtome. In contrast to Epon-812-embedded tissues, Maraglas-Cardolite-embedded tissues can be sectioned in large dimensions with ease and consistent results without "chatter." No background granularity is detectable with high magnification study of Maraglas-Cardolite-embedded tissues. This epoxy is readily stained with lead hydroxide and is relatively stable in the electron beam.
AUTORADIOGRAPHIC STUDY OF DNA SYNTHESIS AND THE CELL CYCLE IN SPERMATOGONIA AND SPERMATOCYTES OF MOUSE TESTIS USING TRITIATED THYMIDINE
Authors: Monesi Valerio
Published: May 2004

Mice were injected intraperitoneally with 15 µc of H3-thymidine. The time course of the labeling in spermatogonia and spermatocytes was studied by using autoradiography on 5 µ sections stained by the periodic acid-Schiff method and hematoxylin over a period of 57 hours after injection. Four generations of type A (called AI, AII, AIII, and AIV), one of intermediate, and one of type B spermatogonia occur in one cycle of the seminiferous epithelium. The average life span is about the same in all spermatogonia, i.e., about 27 to 30.5 hours. The average pre-DNA synthetic time, including the mitotic stages from metaphase through telophase and the portion of interphase preceding DNA synthesis, is also not very different, ranging between 7.5 and 10.5 hours. A remarkable difference exists, however, in the duration of DNA synthesis and of the post-DNA synthetic period. The average DNA synthetic time is very long and is highly variable in type B (14.5 hours), a little shorter and less variable in intermediate (12.5 hours) and AIV (13 hours) spermatogonia, and much shorter and very constant in AIII (8 hours), AII and AI (7 to 7.5 hours) spermatogonia. Conversely, the average post-DNA synthetic time, corresponding essentially to the duration of the prophase, is short and very constant in type B (4.5 hours), longer and variable in intermediate (6 hours) and AIV (8 hours) spermatogonia, and much longer and much more variable in AIII (11 hours), AII and AI (14 hours) spermatogonia. The premeiotic synthesis of DNA takes place in primary spermatocytes during the resting phase and terminates just before the visible onset of the meiotic prophase. Its average duration is 14 hours. No further synthesis of DNA takes place in later stages of spermatogenesis.
ELECTRON MICROSCOPIC OBSERVATIONS OF RAT AND MOUSE CEREBELLUM IN TISSUE CULTURE
Authors: Ross Leonard L. , Bornstein Murray B. , Lehrer Gerard M.
Published: May 2004

Closely ordered stages of myelin formation in cultures of newborn rat and mouse cerebellum, selected by direct light microscopy, were studied with the electron microscope. Electron micrographs of these cultures reveal the presence of neurons, axons, neuroglia, microglia, and ependymal cells. The appearance of the neuron is identical to that previously described in vivo. The neuroglial cell has long, branching processes, and its cytoplasm is characterized by packets of long, narrow fibrils. During myelin formation, a glial cell process surrounds the axon. This process may form an internal mesaxon and may spiral for several turns around the axon. Other glial cell processes may interdigitate with or overlay the innermost process to contribute to the multilamellated structure. The glial processes flatten and the cytoplasmic surfaces of the cell membrane come into contact to form the lamellae of the myelin sheath. These adhesions may be temporarily incomplete as evidenced by sequestered islands of glial cytoplasm among the myelin lamellae. Ultimately, a compact, apparently spiral, myelin sheath is formed. These findings are discussed in relation to in vivo central myelin formation.
ELECTRON MICROSCOPY OF THE UTERINE EPITHELIUM IN THE RABBIT
Authors: Larsen Jørgen Falck
Published: May 2004

The ultrastructure of the uterine epithelium has been studied in estrous, ovariectomized, pregnant, and pseudopregnant rabbits. Tissue for light microscopy was fixed in Bouin's solution and stained with hematoxylin and eosin, by the periodic acid-Schiff (PAS) method, and with methylene blue. Tissue for electron microscopy was fixed in 1 per cent osmium tetroxide in White's saline and embedded in Araldite. The uterine epithelium in estrus is comprised of ciliated and non-ciliated cells. After ovariectomy the epithelium becomes reduced in height and PAS-positive material disappears. Multinucleated cells are formed in the epithelium in pregnancy, pseudopregnancy, and in the non-pregnant horn in unilateral pregnancy. They degenerate during the 3rd week of pseudopregnancy and during the 4th week of pregnancy in the non-pregnant horn. The formation of multinucleated cells is believed to be under hormonal control. The uterine epithelium in contact with the blastocyst changes into a "symplasma," presumably under the influence of a local (chemical?) effect produced by the blastocyst. This change is not seen in pseudopregnancy nor in the non-pregnant horn in unilateral pregnancy. A complex infolding of the basal cell membrane of the epithelium accompanies the "symplasmic" change. The remaining uterine epithelium in pregnancy shows a well developed ergastoplasm suggesting a production of secretion materials, some of which may be available for absorption by the fetus through the yolk sac or paraplacental chorion.
THE INFLUENCE OF ENVIRONMENT ON THE SHELL STRUCTURE OF STARCH GRANULES
Authors: Buttrose M. S.
Published: May 2004

It is well known from light microscope studies of potato starch that the granules formed in a constant environment (of light and temperature) have a ring formation indistinguishable from that of granules formed under field conditions. Electron microscope studies have confirmed that normal potato starch granules have a fine shell structure not usually resolved by the light microscope, and also that shells do not develop in barley granules grown in a constant environment. The paper presented here reports a further study of the dependence of shell formation on environment. Potatoes were grown in a constant environment and starch granules from the newly formed tubers were examined in the light microscope, and in the electron microscope after corrosion by acid. No difference between these granules and normal granules was observed; both wide (light microscope) rings and fine lamellae developed in both granules. Parallel studies were made on wheat starch granules. In this case, shells were not differentiated in granules that developed in a constant environment, but they could be produced at will by imposing a dark period. Thus, shell formation in potato granules must be controlled by an endogenous rhythm, whereas in wheat granules it must be controlled by external environment.
THE EFFECT OF LIGHT INTENSITY AND SUCROSE FEEDING ON THE FINE STRUCTURE IN CHLOROPLASTS AND ON THE CHLOROPHYLL CONTENT OF ETIOLATED LEAVES
Authors: Eilam Yael , Klein S.
Published: May 2004

Changes in the fine structure of proplastids of etiolated leaves exposed to various conditions of light and darkness for 24 and 48 hours were investigated, and the chlorophyll content of the leaves so treated was determined in vivo. The light treatments were given while the leaves were floated on tap water or on a 0.2 M sucrose solution. Leaves floated on water under low light intensity (2 foot-candles) were low in chlorophyll and contained plastids with concentric rows of vesicles. Transferring the leaves back to darkness resulted in the disappearance of the concentric rigs and re-formation of vesicular centers together with straight rows of vesicles and tubules, evenly spaced throughout the stroma. Chloroplasts of leaves floated on a sucrose solution under low light showed large vesicular centers together with stacks of rows of elongated tubules. The same chloroplast structure was found in leaves floated on a sucrose solution in the dark, after having been exposed to weak light for 24 hours. Chlorophyll content in these leaves was the same as in leaves floated on water under high light intensity, where the chloroplasts had normal grana and lamellae. The effect of the investigated factors on plastid development is discussed.
OBSERVATIONS ON THE FINE STRUCTURE OF THE DEVELOPING SPERMATID IN THE DOMESTIC CHICKEN
Authors: Nagano Toshio
Published: May 2004

The kinetic apparatus, the acrosome and associated structures, and the manchette of the spermatid of the domestic chicken have been studied with the electron microscope. The basic structural features of the two centrioles do not change during spermiogenesis, but there is a change in orientation and length. The proximal centriole is situated in a groove at the edge of the nucleus and oriented normal to the long axis of the nucleus and at right angles to the elongate distal centriole. The tail filaments appear to originate from the distal centriole. The plasma membrane is invaginated along the tail filaments. A dense structure which appears at the deep reflection of the plasma membrane is identified as the ring. The fine structure of the ring has no resemblance to that of a centriole and there is no evidence that it is derived from or related to the centrioles. The tail of the spermatid contains nine peripheral pairs and one central pair of tubular filaments. The two members of each pair of peripheral filaments differ in density and in shape: one is dense and circular, and the other is light and semilunar in cross-section. The dense filaments have processes. A manchette consisting of fine tubules appears in the cytoplasm of the older spermatid along the nucleus, neck region, and proximal segment of the tail. The acrosome is spherical in young spermatids and becomes crescentic and, finally, U-shaped as spermiogenesis proceeds. A dense granule is observed in the cytoplasm between acrosome and nucleus. This granule later becomes a dense rod which is interpreted as the perforatorium.
ELECTRON MICROSCOPY OF THE HUMAN SYNOVIAL MEMBRANE
Authors: Barland Peter , Novikoff Alex B. , Hamerman David
Published: May 2004

The structure of the lining cells at the surface of the synovial membrane facing the joint cavity has been studied by electron microscopy. The long cytoplasmic processes of these cells appear to be oriented toward the surface of the membrane, where they overlap and intertwine. The matrix of the lining cells contains dense material but no fibers with the periodicity of collagen. The lining cells are divided into two cell types or states of activity on the basis of their cytoplasmic contents. Type A is more numerous and contains a prominent Golgi apparatus, numerous vacuoles (0.4 to 1.5 microns in diameter) containing varying amounts of a dense granular material, many filopodia, mitochondria, intracellular fibrils, and micropinocytotic-like vesicles. Type B contains large amounts of ergastoplasm with fewer large vacuoles, micropinocytotic-like vesicles, and mitochondria. The probable functions of these cells are discussed in the light of current knowledge of the metabolism and function of the synovial membrane.
THE ORIGIN OF PROTEIN AND FATTY YOLK IN RANA PIPIENS
Authors: Ward Robert T.
Published: May 2004

Study of living frog oocytes with the phase microscope has shown that the early yolk appears in two forms. One of these, the protein yolk, consists of thin, dense, plate-like bodies which in face view are almost always regular hexagons. The other form, the fatty yolk, occurs as clusters of globules of varying sizes. The plate-like bodies occur both singly and in clusters. As the oocytes mature these plate-like bodies grow in size while retaining their hexagonal outline. Mitochondria have been observed to increase in length and numbers as the oocytes mature; they are rods or filaments at all stages of growth up to an oocyte diameter of 300 microns. The oocyte cytoplasm gradually becomes packed with long mitochondria, plate-like bodies, and clusters of globules.
CELL PROLIFERATION AND SPECIALIZATION DURING ENDOCHONDRAL OSTEOGENESIS IN YOUNG RATS
Authors: Young Richard W.
Published: May 2004

Endochondral osteogenesis was studied autoradiographically in ribs and tibiae of 32 Long-Evans rats injected with 1 µc/gm H3-thymidine at 6 days of age and sacrificed at intervals between 1 hour and 2 weeks later. Proliferation and specialization of bone cells were studied by analyses of (a) the percentage of mitoses which were labeled, (b) the percentage of labeled nuclei in bone cells, and (c) grain counts. The following conclusions were derived: The various types of bone cells represent different functional states of the same cell. Cell division is usually restricted to cells in the morphologically unspecialized "osteoprogenitor" state. Specialized bone cells arise by modulation of osteoprogenitor cells. The average cell generation time is shortest in the metaphysis, longest in the periosteum, and intermediate in the endosteum. The average duration of DNA synthesis is relatively constant (about 8 hours). With increasing length of generation time there is a slight increase in G2 + mitosis, but the major change is a lengthening of G1. After dividing, cells in the osteoprogenitor state may remain within the progenitor pool or undergo modulation of cell type, specializing as osteoblasts or becoming incorporated in osteoclasts.
ELECTRON MICROSCOPY AND X-RAY SCANNING MICROANALYSIS OF NEEDLE BIOPSY MATERIAL FROM HUMAN LIVER
Authors: Yasuzumi G.
Published: May 2004

A study has been made of the fine structure of hepatic parenchymal cells of human biopsy material in a case of pancreatic tumor with obstructive jaundice. Dense particles about 60 A in diameter have been found in the cytoplasm, which are considered to be ferritin molecules by electron microscopy. They are encountered throughout the cytoplasmic matrix and are often aggregated in electron-transparent areas, most of which are enclosed by an apparently single-layered membrane. Identification of the elemental iron has been pursued by the application of the x-ray scanning microanalyser which reveals a quantitative value within 1.0 per cent of the pure iron sample. The use of x-ray scanning microanalysis enables one to obtain accurate data from extremely small and precisely defined volumes of biological specimens.
THE VARIATION IN THE STRUCTURE OF ERYTHROCYTE NUCLEI WITH FIXATION
Authors: Davies Howard G. , Spencer Michael
Published: May 2004

Observations have been made on the role of a divalent cation (calcium ion) during OsO4 fixation of nuclei of frog erythrocytes, mainly after isolation from cells. The volume of the nucleus depends partly on the molecular interaction of charged macromolecules, is controlled by the ionic strength of the medium, and hence may be used as a guide in attempts to preserve structure. When the isolation and fixation media contain 0.01 M calcium at pH 6.3 the volume changes, in the light microscope, during processing are small. When the fixative does not contain these ions, reversible volume changes occur during fixation and dehydration. The chromatin of nuclei processed with minimal volume change appears, in the electron microscope, to contain fine dots and lines about 20 to 40 A in diameter, relatively close together. The chromatin structure of nuclei in which volume changes have occurred consists of dense irregularly shaped patches, relatively far apart, and ranging in diameter from about 200 A down to the limits of visibility (20 to 30 A). It is suggested that the latter structure is a precipitation artefact.
SOME STRUCTURAL AND FUNCTIONAL ASPECTS OF THE MITOTIC APPARATUS IN SEA URCHIN EMBRYOS
Authors: Harris Patricia
Published: May 2004

The mitotic figures in dividing cells of sea urchin embryos, from first division to the onset of cilia formation, were studied with regard to the filament system and its relation to kinetochores, chromosomes, and poles, as well as to fixation conditions which would best preserve these structures. With regard to fixation, variations in the salt concentration and pH of the fixative indicated that an extraction effect on the chromosomes noted in earlier work was probably due to a combination of neutral pH and salt concentration equivalent to sea water. The presence of the 15 mµ filaments depended on the presence of either of two stabilizing conditions: pH 6.1 or presence of the salts of sea water, presumably the divalent cations of Ca and Mg. Kinetochores and centrioles were unaffected by the fixative variations. The 15 mµ filaments, reported earlier in the central spindle, are also found in great numbers in the asters of early cleavage divisions. However, with successive divisions and reduction in cell size, the aster disappears at about the 32 to 64 cell stage, and the 15 mµ filaments are entirely associated with the central spindle. This disappearance of the aster suggests that it may be, in fact, merely a specialization of large cells for cytokinesis.
METABOLIC PROPERTIES OF CELLS ISOLATED FROM ADULT MOUSE LIVER
Authors: Berry M. N.
Published: May 2004

Suspensions of isolated cells were prepared from mouse livers that had been perfused via the portal vein with a buffered medium containing sucrose. The demonstration of metabolic activities in these cells was found to be critically dependent on the composition of the suspending medium. The cells showed considerable metabolic activity in a simple medium containing 0.06 to 0.20 M sucrose, but did not respire in 0.30 M sucrose medium. Endogenous respiration was greatest when the sucrose concentration of the medium was 0.10 M or lower and was associated with the formation of acetoacetate. The cells oxidized citric acid cycle intermediates, glutamate, lactate, pyruvate, ß-hydroxybutyrate, α-glycerophosphate, and fatty acids and synthesized urea from ammonium chloride, but carbohydrate substrates did not stimulate oxygen uptake. Cells incubated in Krebs' phosphate-saline did not respire. The lack of respiration in this medium is thought to be related to increased permeability of the cell membrane with penetration of calcium ions and orthophosphate into the cells causing mitochondrial swelling and destruction. Further evidence for the loss of cellular permeability barriers is provided by the demonstration of leakage of certain soluble enzymes into the preparative media.
SYNTHETIC CAPACITIES OF CHROMOSOME FRAGMENTS CORRELATED WITH THEIR ABILITY TO MAINTAIN NUCLEOLAR MATERIAL
Authors: Das Nirmal K.
Published: May 2004

Onion (Allium cepa) and bean (Vicia faba) root tip cells containing many micronuclei, derived from x-ray-induced chromosome fragments, were exposed to H3-thymidine and H3-cytidine to determine the ability of such fragments to undergo DNA and RNA synthesis. Only a few micronuclei in onion and many in bean roots synthesize nucleic acid simultaneously with their main nuclei. A few micronuclei labeled with H3-thymidine undergo mitotic chromosome condensation along with the main nuclei, while the unlabeled ones never do so. The onset of nucleic acid synthesis as well as mitosis in micronuclei appears to be under generalized cellular control. Although all chromosomes and chromosome fragments at telophase give a positive reaction for a silver stainable nucleolar fraction, in the subsequent interphase only some micronuclei, derived from such chromosome fragments, are found to maintain nucleoli; others lose them with time. Those micronuclei which maintain nucleoli, perhaps due to the presence of specific chromosomal regions, are also active in DNA and RNA synthesis. These results are compatible with the concept that nucleoli and associated chromosome regions play an important role in the primary biosynthetic processes of the cell.
SPECULATIONS BASED ON THE MORPHOLOGY OF THE GOLGI SYSTEMS IN SEVERAL TYPES OF PROTEIN-SECRETING CELLS
Authors: Zeigel R. F. , Dalton A. J.
Published: May 2004

Electron microscopical observations on the relationship of the Golgi region to other intracellular organelles in certain protein-secreting cells have substantiated and extended existing hypotheses. In micrographs of several cell types, the juxtanuclear Golgi regions were observed to be closely associated with nuclear "pores." The "transition elements" of the ergastoplasmic membranes possess "blebs" which may represent a transport process facilitating the movement of intracisternal contents into the Golgi zone. A "blebbing" process of this nature may be one source of the small variety of Golgi vesicles. Zymogen granules of different densities were observed and their significance was postulated. Light Golgi vacuoles were observed. It is suggested that these vacuoles represent accumulations of relatively fluid material segregated from the secretory product in these cell types. These hypotheses from inferential evidence are discussed and extended.
LOCALIZED AREAS OF HIGH ALKALINE PHOSPHATASE ACTIVITY IN THE TERMINAL ARTERIAL TREE
Authors: Romanul Flaviu C. A. , Bannister Roger G.
Published: May 2004

Fresh frozen skeletal muscles of rats, rabbits, and humans were sectioned in a cryostat. Sections 12 to 32 micra thick were incubated in a substrate solution for the histochemical demonstration of non-specific alkaline phosphatase activity. A modified azo dye coupling technique was used at pH 9.5. Localized areas of high enzymatic activity were found in specific and well defined areas along the terminal arterial tree, in addition to the activity which has been previously described in capillary endothelium. Arterial branches with luminal diameters of 25 micra or less showed staining of their endothelium starting abruptly at their origin from the parent vessel and fading distally. Smaller arterial branches showed the same localization of enzymatic activity and stained more intensely. Other organs of rats surveyed showed arterial branches with the same pattern of staining. Identical results were obtained using the Gomori technique for alkaline phosphatase. Extensive saline perfusion of the vascular tree did not affect the observed localization of enzymatic activity. The enzymatic activity described may be part of the mechanism regulating the blood flow.
HIGH-RESOLUTION AUTORADIOGRAPHY
Authors: Caro Lucien G. , van Tubergen Robert P.
Published: May 2004

Methods used in obtaining high resolution in autoradiography, with special emphasis on the technique of electron microscopic autoradiography, are described, together with control experiments designed to establish the optimum conditions or procedures. On the basis of these experiments the emulsion selected was Ilford L-4, with a crystal size slightly larger than 0.1 micron. It is applied to the specimen in the form of a gelled film consisting of a monolayer of silver halide crystals. Background, when present, can be eradicated by a simple method. The preparations can be stored, in presence of a drying agent, at room temperature or in a refrigerator. Photographic development is done in Microdol, or in a special fine grain "physical" developer. For examination in the electron microscope the sections are stained with uranyl or lead stains. These methods give a good localization of the label, at the subcellular level, and good reproducibility in relative grain counts.