bluuebunny/crossref_metadata_2025_split huggingface dataset:
CYTOCHEMICAL STUDIES OF MITOCHONDRIA
Authors: Watson Michael L. , Siekevitz Philip 
Published: May 2004

Mitochondria isolated from rat liver and suspended in 0.44 M sucrose were disrupted by treatment with 0.3 per cent Na deoxycholate. The treated suspension was fractionated by differential centrifugation into a number of fractions and the respective pellets were examined in sections in the electron microscope.
One of these fractions was found to consist of apparently membrane-bound (vesicular) elements.
The difference between interfaces and membranes was discussed and the material of this fraction was found to meet stated requirements identifying it as membranous.
A detailed study of the disruption process undergone by mitochondria in the presence of Na deoxycholate showed that the elements of this fraction were derived from structural elements assumed to be mitochondrial membranes.
The findings thus demonstrate that mitochondria do possess membranes as defined and that these membranes can be isolated in a relatively pure form.
DNA IN GAMETOGENESIS AND EMBRYOGENY IN TRADESCANTIA
Authors: Woodard John W. 
Published: May 2004

A microphotometric study of various Feulgen-stained gametophytic and sporophytic nuclei of Tradescantia paludosa was made to test the hypothesis that DNA is maintained in multiples of a basic unit within all cells of an organism.
A multiple relationship was found in all tissues analyzed. The lowest amount of DNA was found in gametophytic nuclei, approximately twice and four times this amount in sporophytic nuclei, and approximately three and six times this amount in endosperm nuclei. Intermediate amounts of DNA were found only in tissues presumably undergoing an interphase synthesis of DNA preceding either cell division or endomitosis.
It is concluded that within the limitations of present methods of measurement, DNA amounts show a quantitative behavior which supports the "constancy" hypothesis. Such quantitative stability of DNA gives support to the concept that DNA is associated with the stable elements of the gene.
FORMATION OF MYELIN IN THE CENTRAL NERVOUS SYSTEM OF MICE AND RATS, AS STUDIED WITH THE ELECTRON MICROSCOPE
Authors: Luse Sarah A. 
Published: May 2004

Sections of brain and spinal cord of mice and rats at 1, 3, 5, and 17 days after birth were examined with the electron microscope. In the early stages of myelinization only two to four lamellae surround the axon. These laminae are formed from the plasma membraces of glial processes, and in particular of oligodendroglial processes. In a later stage of myelinization a larger number of flattened glial processes surround the axon with enclosed cytoplasm trapped within some of the membranes. Multiple extensions of the membranes of the flattened glial processes to the lamellae of the myelinated sheath are evident at this stage, with a variable number of membranes within the sheath at various positions along the fiber.
Newly formed myelinated sheaths are sometimes larger than their enclosed fibers, extending as a projection of sheath which does not surround axoplasm. Loci are present in which the myelinated sheath is incomplete or interrupted.
ELECTRON MICROSCOPIC OBSERVATIONS ON THE SUBMICROSCOPIC MORPHOLOGY OF THE MEIOTIC NUCLEUS AND CHROMOSOMES
Authors: De Robertis E. 
Published: May 2004

Thin sections of the testicular follicles of the grasshopper Laplatacris dispar were studied under the electron microscope. In the primary spermatocytes, during meiotic prophase, three main regions can be recognized within the nucleus: (1) the nucleolus and associated nucleolar material; (2) the interchromosomal regions with the dense particles; and (3) the chromosomes.
The nucleolus is generally compact and is surrounded by nucleolar bodies that comprise aggregations of dense round particles 100 to 250 A in diameter. A continuous transition can be observed between these particles and those found isolated or in short chains in the interchromosomal spaces. Particles of similar size (mean diameter of 160 A) can be found associated with the nuclear membrane and in the cytoplasm.
The chromosomes show different degrees of condensation in different stages of meiotic prophase. The bulk of the chromosome appears to be made of very fine and irregularly coiled filaments of macromolecular dimensions. Their length cannot be determined because of the thinness of the section but some of them can be followed without interruption for about 1000 to 2000 A. The thickness of the chromosome filaments seems to vary with different stages of prophase and in metaphase. In early prophase, filaments vary between 28 ± 7 A and 84 ± 7 A with a mean of 47 A, in late prophase the mean is about 70 A. In metaphase the filaments vary between 60 and 170 A with a mean of about 100 A. Neither the prophase nor the metaphase chromosomes have a membrane or other inhomogeneities.
The finding of a macromolecular filamentous component of chromosomes is discussed in relation to the physicochemical literature on nucleoproteins and nucleic acids and as a result it is suggested that the thinnest chromosome filaments (28 ± 7 A) probably represent single deoxyribonucleoprotein molecules.
A SPECIAL FIBRIL OF THE DERMIS
Authors: Palade George E. , Farquhar Marilyn G. 
Published: May 2004

A new type of extracellular fibril is described in the dermis of Bufo marinus, Rana pipiens, and Amblystoma punctatum. It is restricted in distribution to the dermal micropapillae and the region immediately below them in the stratum spongiosum. The fibrils (diameter = 200 to 750 A) are lateral aggregates of fine filaments and have a unique banding pattern characterized by absence of recognizable periodicity and by polarization in respect to the basement membrane. Their distal1 ends are anchored in the basement membrane, and their proximal ends converge in knots located in the middle region of the micropapillae. These anchoring fibrils seem to secure the minute outfoldings of the basement membrane along the dermal-epidermal junction.
Comparable, but less frequent, fibrils are also encountered along the proximal aspect of the basement membrane in the skin, lingual mucosa, and mucosa of the gastric fundus in the rat.
AN ELECTRON MICROSCOPE STUDY OF THE EMBRYOLOGY OF THE INTERCALATED DISC IN THE HEART OF THE RABBIT
Authors: Muir Alan R. 
Published: May 2004

Prenatal and postnatal cardiac muscle from rabbits has been studied by electron microscopy, after osmium fixation and methacrylate embedding. The observations showed that
1. Cell membranes divide the muscle into cellular units from the youngest embryo which was studied (9½ days after coitus) until the adult state.
2. The embryonic muscle cells contain only one nucleus, whereas the adult cell may be multinucleated.
3. At all stages of development, wherever a myofibrillar axis crosses a cellular boundary, the myofilaments are interrupted by an intercalated disc.
4. With age, increase in size and complexity of the discs render them recognisable by the light microscope.
EFFECT OF GAMMA IRRADIATION ON THE DESOXYRIBONUCLEASE II ACTIVITY OF ISOLATED MITOCHONDRIA
Authors: Okada Shigefumi , Peachey Lee D. 
Published: May 2004

1. Exposure of isolated liver mitochondria to high doses of gamma rays from a Co60 source causes the level of DNase II activity to increase. Treatment of the mitochondria with sonic vibration causes a further elevation of the activity to a level which is independent of the prior radiation dose.
2. Such increased mitochondrial DNase II activity appears to be due to the "structural damage" of the subcellular particulates caused by the ionizing radiation. Other methods of disrupting the mitochondrial structure also cause increased DNase II activity. A causal relationship between the structural alteration and the increased enzymatic activity is postulated.
3. The DNase II activity appears to be closely associated with the structural elements of the mitochondria and remains associated with the fragments after irradiation.
4. Upon irradiation, the mitochondrial suspension releases ultraviolet-absorbing materials which are probably nucleotide in nature.
5. The possibility of localization of DNase activity in the lysosome fraction of de Duve (15) is discussed. It is felt that DNase II is at least in part a mitochondrial enzyme and that probably the conclusions drawn here would be applicable to any DNase II present in the lysosomes as well.
6. Irradiation of whole liver homogenate causes no increased DNase II activity. The experiments do not provide any information on the presence or action of protective substances in the homogenate.
EXPERIMENTALLY INDUCED CHROMOSOME ABERRATIONS IN PLANTS
Authors: Kihlman B. A. 
Published: May 2004

The finding of Lilly and Thoday that potassium cyanide produces structural chromosome changes in root tips of Vicia faba was confirmed. Like mustards, diepoxides, and maleic hydrazide, potassium cyanide seems to act on cells at early interphase. A tendency of cyanide breaks to be concentrated in heterochromatic segments of the chromosomes was evident. The production of chromosome aberrations by cyanide proved to be practically unaffected by the temperature during treatment. In agreement with Lilly and Thoday, the effect of potassium cyanide was found to be dependent on oxygen tension during treatment. The effect of potassium cyanide increases with increasing oxygen concentration up to 100 per cent oxygen. In the absence of oxygen, potassium cyanide was not completely inactive, but produced a low, though significant frequency of aberrations. Pretreatments with 2.4-dinitrophenol did not influence the effect of potassium cyanide.
When bean roots were treated with potassium cyanide before a treatment with 8-ethoxycaffeine, or at the same time as they were treated with 8-ethoxycaffeine, the effect of 8-ethoxycaffeine was almost completely suppressed.
The effects of a number of other heavy metal complexing agents were also tested. Sodium fluoride, potassium thiocyanate, carbon monoxide, o-phenanthroline, 2.2-bipyridine, and sodium azide were without radiomimetic effect under the conditions employed, and so was a mixture of sodium azide and sodium fluoride. A low, but quite significant, radiomimetic effect was obtained after treatments with sodium diethyldithiocarbamate, cupferron, and 8-hydroxyquinoline. Under anaerobic conditions, the effects of cyanide and cupferron were both quantitatively and qualitatively indistinguishable. Unlike the effect of cyanide, the effect of cupferron was not enhanced by the presence of oxygen.
The effects of the same heavy metal complexing agents were tested on the activities of the enzymes catalase and peroxidase. The activities of both of these enzymes were found to be totally inhibited only by potassium cyanide. In the other cases, little correlation was found between ability to inhibit the activities of these enzymes and ability to produce chromosome aberrations.
In a number of experiments, hydrogen peroxide was found to be without radiomimetic effect, whether alone or in combination with potassium cyanide. t-Butyl hydroperoxide proved to be active. The effect of t-butyl hydroperoxide was substantially increased by pretreatments with 2.4.-dinitrophenol.
The results are discussed, and it is concluded that the observations made do not support the hypothesis that hydrogen peroxide is involved in the production of chromosome aberrations by potassium cyanide. The possibility that organic peroxides are involved cannot be excluded on the bases of the experimental results. As an alternative hypothesis, it is suggested that iron or other heavy metals are present in the chromosomes and that cyanide and other heavy metal complexing agents produce chromosome aberrations by reacting with these metals.
STRUCTURE AND DEVELOPMENT OF THE CHLOROPLAST IN CHLAMYDOMONAS
Authors: Sager Ruth , Palade George E. 
Published: May 2004

The cytoplasmic organization of a normal green strain of the alga Chlamydomonas reinhardi has been investigated with the electron microscope using thin sections of OsO4 fixed material.
The detailed organization of the chloroplast has been of special interest. The chloroplast, a cup-shaped organelle, surrounded by a double membrane, consists of: (1) discs about 1 micron in diameter, considered to represent the basic structural unit of the chloroplast, and each composed of a pair of membranes joined at their ends to form a flat closed vesicle; the discs are grouped into stacks resembling the grana of higher plants; (2) matrix material of low density in which the discs are embedded; (3) starch grains; (4) the pyrenoid, a non-lamellar region associated with starch synthesis, and containing tubules which connect with the lamellae; (5) the eyespot, a differentiated region containing two or three plates of hexagonally packed, carotenoid-containing granules, located between discs, and associated with phototaxis.
In addition to the chloroplast, the cytoplasm contains various membranous and granular components, including mitochondria, endoplasmic reticulum, and dictyosomes, identified on the basis of morphological comparability with structures seen in animal cells. The nucleus, not investigated in detail in this study, contains a large, granular nucleolus and is surrounded by a nuclear envelope which is provided with pores and exhibits instances of continuity with the endoplasmic reticulum of the cytoplasm.
A STUDY OF THE STRUCTURE OF SPLENIC SINUSES IN MAN AND IN THE ALBINO RAT WITH THE LIGHT MICROSCOPE AND THE ELECTRON MICROSCOPE
Authors: Weiss Leon 
Published: May 2004

The splenic sinuses in the spleens of 5 human beings and 7 albino rats have been studied in the light microscope and electron microscope after fixation in Dalton's fluid and Palade's fluid and embedding in n-butyl methacrylate.
Splenic sinuses are tortuous vascular channels of large but variable diameter which represent the first venous vessels in the spleen and make up almost the entire red pulp in man and in rats. These vessels are composed of reticulo-endothelial cells flattened to endothelial form and sheathed by a netted reticulum. The luminal surface of the endothelium is made highly irregular by delicate and variable cytoplasmic protrusions, slender corridors separating adjacent endothelial cells, anastomotic openings to other sinuses, bulgings of entire cells, and even thrusts of endothelium spanning the sinai lumen. The supporting reticulum presents a well developed latticed appearance in tangential sections of sinuses, but in most cuts is punctate or linear.
The reticulum is composed of strands without limiting membranes, which, in substance, are amorphous and resemble basement membrane. Material identical in appearance to the substance of the reticulum may be present in the endothelium, suggesting that the reticulum is formed by endothelial cells. The endothelium also contains deposits of presumed ferritin and hemosiderin. The extreme luminal bulgings of endothelium suggest production of circulating monocytes or lymphocytes by detachment of endothelial cells.
Sinuses are patent and collapsed to varying degrees. Patent sinuses are separated by collapsed sinuses and these collapsed sinuses appear to constitute splenic (Billroth) cords.
TOPOGRAPHY OF THE ORGANIC COMPONENTS IN MOTHER-OF-PEARL
Authors: Grégoire Charles 
Published: May 2004

1. The topography of the organic components (conchiolin) has been investigated on positive, postshadow-cast, formvar, and carbon replicas of mother-of-pearl from shells of a Cephalopod, of two Gastropods, and of six Pelecypods. All these shells are characterized by a true nacreous inner shell layer.
2. The material included normal shell surfaces, fragments of cleavage obtained by fracture, and surfaces polished tangentially and transversally to the inner surface of the shells. Replicas of these surfaces were prepared before and after etching of graded heaviness, induced by a chelating agent (sequestrene NA 2, titriplex III). Micrographs of the successive steps of the process of corrosion have been recorded.
3. Corrosion unmasked, on the nacreous surfaces, organic membranes or sheets, running as continuous formations in between adjacent mineral lamellae, and separating the individual crystals of aragonite which are aligned in rows and constitute each lamella.
4. The interlamellar sheets of material exhibit a reticulated structure, which is especially visible in preparations orientated tangentially to the lamellae and to the tabular surface of the aragonite crystals. The pattern of this lace-like structure, different in the various species studied, appeared in the same species as closely similar to that reported previously in leaflets of thoroughly decalcified mother-of-pearl, dissociated by ultrasonic waves. The present results support former conclusions with regard to the existence of taxonomic differences between Cephalopods, Gastropods, and Pelecypods in the morphological organization of the organic phase within mother-of-pearl.
The Spermatid Cell Membrane in Melanoplus differentialis
Authors: Roth L. E. 
Published: May 2004

1. The cell membrane of the spermatid of the grasshopper Melanoplus differentialis is shown to be composed of a double-layered membrane 10 mµ thick. Closely applied to this is an additional outer covering 25 to 35 mµ thick which has a regular geometrical pattern.
2. Models of cell membrane structure are discussed briefly. It is suggested that the pattern results from preferential adsorption of material onto a particular component of the double-layered membrane.
ARCHITECTURE AND NERVE SUPPLY OF MAMMALIAN SMOOTH MUSCLE TISSUE
Authors: Caesar Rudolf , Edwards George A. , Ruska Helmut 
Published: May 2004

Smooth muscle tissue from mouse urinary bladder, uterus, and gall bladder has been studied by means of the electron microscope. The smooth muscle cells are distinctly and completely separated from each other by a cytolemma comparable to the sarcolemma of striated muscle. The tissue is thus cellular and not syncytial. With this evidence, supported by electron microscopy of other tissues, we question the existence of true syncytia in animal tissues. Individual cell membranes necessary for the electrophysiologic events exist in smooth muscle, and its nerve and conduction in a tissue such as uterus or bladder can occur at the cellular level as well as at the tissue area level.
The smooth muscle cell contains myofilaments, nucleus, endoplasmic reticulum, mitochondria, Golgi complex, centrosome, and pinocytotic vesicles. These structures are described in some detail, and their probable interrelations and functions are discussed.
The autonomic nerves innervating smooth muscle cells are composed of axons and lemnoblasts. The axon is suspended by the mesaxon formed by the infolded plasma membrane of the lemnoblast. The respective plasma membranes separate axon and lemnoblast from each other and from surrounding muscle cells. The axons of autonomic nerves never penetrate the plasma membrane of the muscle cell, but pass or intrude into muscle cell pockets, forming a contact between axonal plasma membrane and smooth muscle plasma membrane. The lemnoblast shows well developed endoplasmic reticulum with Palade granules, mitochondria, and a long, elliptical nucleus. The axon contains neurofilaments, mitochondria, and synaptic vesicles; the quantity of the latter two being significantly greater in the periphery of lemnoblasts and near axon-muscle contact regions. We regard the contact regions as the synapses between the autonomic nerves and the smooth muscle cells.
STUDIES ON THE BIOSYNTHESIS OF COLLAGEN
Authors: Jackson Sylvia Fitton , Smith R. H. 
Published: May 2004

1. A tissue culture method was devised in which suspensions of osteoblasts, obtained directly from frontal bones of fowl embryos, were grown in a fluid, fibrin-free medium.
2. Maximum growth of the tissue, as measured by dry weight, with the formation of collagen protein, based on the estimation of hydroxyproline, was obtained in periods of up to 6 days.
3. Appreciable amounts of protein-bound hydroxyproline were formed during the first 24 hour growth period, but electron microscopy of portions of the same cultures failed to demonstrate the presence of any typical collagen fibrils.
4. The subsequent formation of many characteristic collagen fibrils was not associated with a significant rise in the mean hydroxyproline content of the tissue.
5. The cytoplasmic granules of the osteoblasts stained intensely with the P.A.S. technique when the collagen fibrils were being formed.
6. It is suggested that collagen-forming cells synthesise and secrete a hydroxyproline-rich precursor of protein or large peptide nature, which subsequently becomes directly transformed into typical collagen fibrils.
STUDIES ON THE BIOSYNTHESIS OF COLLAGEN
Authors: Smith R. H. , Jackson Sylvia Fitton 
Published: May 2004

1. Fowl osteoblasts grown in bulk tissue cultures in the presence of 14C-(L)-proline incorporated this amino acid into peptide linkage. A significant amount of the incorporated radioactivity was found in the hydroxyproline, glutamic acid, and aspartic acid fractions of the cultures.
2. The rate of formation of protein-bound 14C-hydroxyproline from 14C-(L)-proline was maximal in cultures grown for 15 hours and fell exponentially with the increasing age of the cultures.
3. 14C-(L)-glutamic acid was incorporated by the osteoblast cultures, but no significant amount was converted to hydroxyproline.
THE ULTRASTRUCTURE OF THE VITELLINE BODY IN THE OOCYTE OF THE SPIDER TEGENARIA PARIETINA
Authors: André Jean , Rouiller Charles 
Published: May 2004

The vitelline body in the mature oocyte of the spider Tegenaria parietina is composed of 4 different zones.
1. The central zone contains granular areas, vesicles, and a few lamellae.
2. The lamellar zone consists of numerous concentric lamellae. These sheets, 45 A in thickness, are stacked in groups. The fine structure and the regular arrangement recall those of myelin sheets, retinal rods, and chloroplasts. Between the stacks of lamellae, finely granular masses and various vesicles are to be found.
3. The "zone of transition" consists of a finely granular substance accumulated in abundant masses. This substance is composed of very closely packed granules about 50 to 60 A in diameter. Very often, near the lamellae, the granules show alignment giving a gradual transition from grains to lamellae.
4. The vesicular zone contains ergastoplasm, dense particles, mitochondria, and Golgi material. It is suggested that the peculiar ultrastructure of these cytoplasmic components may be related to an intense metabolic activity.