bluuebunny/crossref_metadata_2025 huggingface dataset:
AN ELECTRON MICROSCOPE STUDY OF CALF THYMUS NUCLEAR PREPARATIONS ISOLATED IN SUCROSE SOLUTIONS
Authors: Kodama Robert M. , Tedeschi Henry
Published: May 2004

This work was carried out with the intent of developing a method capable of routinely evaluating calf thymus nuclear preparations with the electron microscope. Examination of small random samples, pre-embedded in agar after fixation with permanganate, were found to give results comparable to those obtained with much larger samples withdrawn randomly from pellets and embedded and sectioned conventionally. Results obtained by this pre-embedding technique with acrolein, osmium tetroxide, or permanganate fixations were equivalent. Calf thymus nuclear preparations isolated in sucrose by the method prevalently used (see 1) are contaminated only slightly with intact cells, to a degree which varies with each preparation. However, intact cells, damaged cells, or nuclei with some cytoplasm constitute together about 30 per cent of the preparation. Particles other than intact cells are not readily distinguishable from one another by light or phase microscope techniques. These preparations can be purified further by centrifuging through a dense sucrose layer. In our hands, however, contamination with some cytoplasm still remains in approximately 10 per cent of the particles. Incubation of the particles prepared without purification procedures, under conditions frequently used, results in the extensive breakdown of particles. Under at least one set of conditions, nuclei are selectively disrupted, leaving primarily damaged cells in the preparation.
NON-IDENTICAL MECHANISMS OF MITOTIC ARREST BY RESPIRATORY INHIBITORS IN PEA ROOT TIPS AND SEA URCHIN EGGS
Authors: Amoore J. E.
Published: May 2004

The adenosine triphosphate (ATP) content of pea root tips is about 0.40 mmole/kg fresh weight. The effects of partial and complete anaerobiosis, and of carbon monoxide and hydrogen cyanide, on the ATP level are described. The ATP content was shown to correspond closely to the oxygen uptake under these conditions. However, there was no relation between the ATP level and the rate of mitosis, a situation which is in contrast with that in sea urchin eggs. In anaerobic conditions, mitoses in pea root tips could continue at a reduced rate, even though the ATP content had fallen to 1.5 per cent of the normal value in air The ATP level in anaerobic conditions corresponded closely to the expected rate of ATP regeneration from known anaerobic sources of energy. Calculations show that even this severely restricted supply of energy would be more than adequate to drive the anaphase chromosome movements, so it is suggested that the concept of a mitotic energy reservoir is superfluous in root tips. No evidence could be found for the involvement during mitosis in sea urchin eggs of a non-respiratory ferrous complex such as occurs in pea root tips. Hence the dilemma remains, that whereas mitoses in both sea urchin eggs and pea root tips are arrested by respiratory inhibitors, yet the biochemical mechanisms of the arrest in the two types of cell are totally distinct.
OBSERVATIONS ON THE FINE STRUCTURE OF PHARYNGEAL MUSCLE IN THE PLANARIAN DUGESIA TIGRINA
Authors: MacRae Edith Krugelis
Published: May 2004

Pharyngeal muscle of the planarian Dugesia tigrina was studied by electron microscopy after osmium tetroxide fixation. The muscle cell was observed to contain one myofibril or bundle of myofilaments parallel to its longitudinal axis. The myofilaments were of two types, different in size and distribution. No Z lines or myofilament organization into cross or helical striations were seen. Dense bodies were seen as projections from an invagination of the plasma membrane and as dense lines parallel to the myofilaments. The muscle cells are surrounded by a plasma membrane which is structurally associated with dense body projections, with vesicles and cisternae of sarcoplasmic reticulum, and with synaptic nerve endings. The cell has sarcoplasmic projections perpendicular to its long axis; these projections are seen to contain the nucleus or mitochondria and granules. Mitochondria and granules are also seen in a sarcoplasm rim around the fibril. The dense bodies may serve as attachment for thin myofilaments and function in transmission of stimuli from plasma membrane to the interior of the fibril.
THE DIFFERENTIATION OF WHITE ADIPOSE CELLS
Authors: Napolitano Leonard
Published: May 2004

Differentiating white adipose tissue from presumptive and developing fat pads of newborn and young rats was fixed in buffered osmium tetroxide, embedded in Vestopal W, and examined in an electron microscope. Pre-adipose cells were found to be fibroblasts characterized by their spindle shape, long tenuous cytoplasmic extensions, and profuse endoplasmic reticulum. The developmental stages traced from fibroblast to mature adipose cell show a gradual change in cell shape, an accumulation of cytoplasm and non-membrane-bounded lipid, a decrease in the endoplasmic reticulum, and a change in shape of mitochondria. Transitory glycogen appears at mid-differentiation. Numerous smooth-membraned vesicles occur in the cytoplasm throughout differentiation. Pinocytosis is constantly evident. Cells of the multilocular stage are shown to differ from brown fat cells, particularly with respect to cytoplasmic membrane systems and mitochondria. No transport of particulate lipid from the lumen of the capillary to, or within, the adipose cell was detected, nor could any cell organelle be demonstrated to be visibly related to lipid synthesis and/or deposition.
THE CELL ENVELOPES OF TWO EXTREMELY HALOPHILIC BACTERIA
Authors: Brown A. D. , Shorey C. D.
Published: May 2004

The cell envelope of Halobacterium halobium was seen in thin sections of permanganate-fixed cells to consist of one membrane. This membrane appeared mostly as a unit membrane but in a few preparations it resembled a 5-layered compound membrane. The cell envelope of Halobacterium salinarium at high resolution was always seen as a 5-layered structure different in appearance from the apparent compound membrane of H. halobium. The "envelopes" which were isolated in 12.5 per cent NaCl from each organism were indistinguishable from each other in the electron microscope and comprised, in each case, a single unit membrane with an over-all thickness of about 110 A. Some chemical analyses were made of isolated membranes after freeing them from salt by precipitating and washing with trichloroacetic acid. Such precipitated membranes consisted predominantly of protein, with little carbohydrate and no peptido-aminopolysaccharide (mucopeptide). Sectioned whole cells of H. halobium contained intracellular electron-opaque structures of unknown function.
THE OCCURRENCE OF A SUBUNIT PATTERN IN THE UNIT MEMBRANES OF CLUB ENDINGS IN MAUTHNER CELL SYNAPSES IN GOLDFISH BRAINS
Authors: Robertson J. David
Published: May 2004

Observations additional to those previously reported (34) on boutons terminaux and club endings on Mauthner cell lateral dendrites, primarily as seen in sections of permanganate-fixed material, are described. Certain new findings on OSO4-fixed endings are also included. The boutons terminaux are closely packed in the synaptic bed with ∼ 100 to 150 A gaps between their contiguous unit membranes and a few interspersed glial extensions. Their synaptic membrane complexes (SMC) appear as pairs of unit membranes separated by ∼ 100 to 150A clefts. They contain many vesicles and unoriented mitochondria, but no neurofilaments. The club endings after KMnO4 fixation are, as after OSO4 fixation (34), again seen surrounded by a layer of extracellular matrix material. These endings contain relatively few synaptic vesicles, a few unit membrane limited tubules ∼ 300 A in diameter, and mitochondria oriented perpendicular to the SMC. Neurotubules and neurofilaments are not clearly seen. These components are also virtually absent in the Mauthner cytoplasm. No ribosomes are seen in the KMnO4-fixed material. The unit membranes of the SMC of club endings show up clearly in essentially the same junctional relations described after formalin-OSO4 fixation (34). In addition, the synaptic discs in transverse section show a central beading repeating at a period of ∼ A associated with scalloping of the cytoplasmic surfaces. In oblique views, dense lines are seen repeating at a period of ∼ 90 A. In frontal views a hexagonal array of close-packed polygonal facets is seen. These repeat at a period of ∼ 95 A. Each has a central dense spot <25 A in diameter. Similar subunits are seen in the unit membranes of synaptic vesicles.
HALE STAIN FOR SIALIC ACID-CONTAINING MUCINS
Authors: Gasic Gabriel , Berwick Leonard
Published: May 2004

The feasibility of using the Hale stain to identify cellular sialic acid-containing mucins by electron microscopy was investigated. Three kinds of mouse ascites tumor cells were fixed in neutral buffered formalin, exposed to fresh colloidal ferric oxide, treated with potassium ferrocyanide, imbedded in Selectron, and sectioned for electron microscopy. Additional staining with uranyl acetate and potassium permanganate was done after sectioning in order to increase contrast. Those cells known to be coated with sialomucin showed deposits of electron-opaque ferric ferrocyanide crystals in the areas where sialomucin concentrations were expected. When these cells were treated with neuraminidase beforehand, these deposits did not appear. It was concluded that, with the precautions and modifications described, the Hale stain can be successfully combined with electron microscopy to identify sialomucin.
POPULATION DYNAMICS OF INTESTINAL EPITHELIA IN THE RAT TWO MONTHS AFTER PARTIAL RESECTION OF THE ILEUM
Authors: Loran M. R. , Crocker T. T.
Published: May 2004

Sprague-Dawley rats that had been subjected 2 months previously to partial resection (10 per cent) of the small intestine and an equal number of control rats were injected with tritiated thymidine and sacrificed at intervals during the subsequent 16 hours. Segments of duodenum, jejunum and ileum were prestained by the Feulgen technique and radioautographed. The proportion of crypt cells bearing labeled nuclei, the percentage of labeled crypt cells in mitosis and the appearance of labeled crypt cells on the villi were determined. Comparison of control and resected rats showed that (a) the proportion of intestinal crypt cells incorporating thymidine was considerably greater and uniformly high throughout the shortened intestine, (b) the life cycle of crypt cells was slightly reduced, and was uniform throughout the shortened intestine, and (c) the time during which cells were retained in crypts was markedly reduced. On the basis of persistent, generalized increase in the production of crypt cells, and on prior evidence that the epithelial cells of shortened intestine continue to have a brief life span and evidence of metabolic immaturity, the existence of a humoral factor, tentatively called "intestinal epithelial growth hormone," is postulated.
BRAIN MITOCHONDRIA
Authors: Stahl W. L. , Smith J. C. , Napolitano L. M. , Basford R. E.
Published: May 2004

Two methods of preparing a mitochondrial fraction from beef brain cortex are described. Data are presented on the rate of oxidation of substrates, P/O and respiratory control ratios, cholinesterase activity, and DNA content. Electron micrographs of isolated mitochondria and mitochondria in situ are shown. Comparisons are drawn between these preparations and mitochondria prepared in 0.25 M sucrose. The data on enzymic properties and contamination by non-mitochondrial material indicate that mitochondrial fractions which compare favorably with those from other tissues can be prepared from brain tissue.
ROLE OF THE GAMETE MEMBRANES IN FERTILIZATION IN SACCOGLOSSUS KOWALEVSKII (ENTEROPNEUSTA)
Authors: Colwin Laura Hunter , Colwin Arthur L.
Published: May 2004

An earlier paper showed that in Saccoglossus the acrosomal tubule makes contact with the egg plasma membrane. The present paper includes evidence that the sperm and egg plasma membranes fuse to establish the single continuous zygote membrane which, consequently, is a mosaic. Contrary to the general hypothesis of Tyler, pinocytosis or phagocytosis plays no role in zygote formation. Contact between the gametes is actually between two newly exposed surfaces: in the spermatozoon, the surface was formerly the interior of the acrosomal vesicle; in the egg, it was membrane previously covered by the egg envelopes. The concept that all the events of fertilization are mediated by a fertilizin-antifertilizin reaction seems an oversimplification of events actually observed: rather, the evidence indicates that a series of specific biochemical interactions probably would be involved. Gamete membrane fusion permits sperm periacrosomal material to meet the egg cytoplasm; if an activating substance exists in the spermatozoon it probably is periacrosomal rather than acrosomal in origin. The contents of the acrosome are expended in the process of delivering the sperm plasma membrane to the egg plasma membrane. After these membranes coalesce, the sperm nucleus and other internal sperm structures move into the egg cytoplasm.
CORRELATION OF FINE STRUCTURE AND PHYSIOLOGY OF THE INNERVATION OF SMOOTH MUSCLE IN THE GUINEA PIG VAS DEFERENS
Authors: Merrillees Neil C. R. , Burnstock Geoffrey , Holman Mollie E.
Published: May 2004

An electron microscope study of the innervation of smooth muscle of the guinea pig vas deferens was undertaken in order to find a structural basis for recent electrophysiological observations. The external longitudinal muscle coat was examined in transverse section. Large areas of the surfaces of adjacent muscle cells were 500 to 800 A apart. Closer contacts were rare. A special type of close contact suggested cytoplasmic transfer between neighbouring cells. Groups of non-myelinated axons from ganglia at the distal end of the hypogastric nerve ramified throughout the muscle. Some small axon bundles and single axons lay in narrow fissures within closely packed muscle masses. Many axons contained "synaptic vesicles." About 25 per cent of the muscle fibres in the plane of section were within 0.25 µ of a partly naked axon; of these 15 per cent were within 500 A of the axon, and about 1 per cent made close contact (200 A) with a naked axon. It is unlikely that every muscle fibre is in close contact with an axon, and it is not possible for every fibre to have many such contacts. Muscle fibres are probably activated by both diffusion of transmitter from naked portions of axons a fraction of a micron distant, and electrotonic spread of activity from neighbouring cells.
ULTRASTRUCTURAL STUDIES ON THE BLUE-GREEN ALGAL SYMBIONT IN CYANOPHORA PARADOXA KORSCHIKOFF
Authors: Hall William T. , Claus George
Published: May 2004

Studies conducted on the ultrastructure of Cyanophora paradoxa Korschikoff (a cryptomonad) have shown that its intracellular symbiont is closely related to unicellular blue-green algae. Due to its peculiar habitat, the intracellular symbiont lacks the characteristic cyanophycean double-layered cell wall, but is surrounded by a thin protoplasmic membrane. The protoplasm itself is differentiated into a lamellated chromatoplasm containing photosynthetic pigments, polyphosphate granules, and possible oil droplets, and a non-lamellar centroplasm with a large centrally located electron-opaque body surrounded by a fibril-containing halo. This halo-central body complex may be nuclear in nature. Binary fission of the organism is described. Since this cyanelle has not yet been classified, we name it Cyanocyta korschikoffiana nov. gen. nov. sp.; and because of its structural peculiarities, we find it necessary to create a new family for it, Cyanocytaceae, in the order Chroococcales.
INTRAMITOCHONDRIAL FIBERS WITH DNA CHARACTERISTICS
Authors: Nass Margit M. K. , Nass Sylvan
Published: May 2004

Chick embryo mitochondria, studied with the electron microscope, show crista-free areas of low electron opacity. These areas are observable after fixation with osmium tetroxide, calcium permanganate, potassium permanganate, formaldehyde, acrolein, acrolein followed by osmium tetroxide, uranyl acetate followed by calcium permanganate, and acetic acid-alcohol. Staining of sections with lead hydroxide or uranyl acetate, or with both, resulted in an increased density of a fibrous material within these areas. The appearance of the fibrous structures varied with the fixative employed; after fixation with osmium tetroxide the material was clumped and bar-like (up to 400 A in diameter), whereas after treatment of osmium tetroxide-fixed tissues with uranyl acetate before dehydration the fibrous structures could be visualized as 15 to 30 A fibrils. Treatment with ethylenediaminetetraacetate (EDTA) in place of uranyl acetate coarsened the mitochondrial fibrils. After fixation with calcium permanganate or potassium permanganate, or a double fixation by uranyl acetate followed by calcium permanganate, the fibers appeared to have a pattern and ultrastructure similar to that observed after the osmium tetroxide-uranyl acetate technique, except that some of them had a slightly greater diameter (up to 50 A). Other fixatives did not preserve the fibers so well. The fibers appeared strongly clumped by formaldehyde fixation, and were difficult to identify after fixation with acrolein or acetic acid-alcohol. The staining of nucleic acid-containing structures by uranyl acetate and lead hydroxide was improved by treatment of osmium tetroxide-fixed sections with hydrogen peroxide, and the mitochondrial fibers also had an increased density in the electron beam after this procedure. The staining characteristics suggest the fibrous material of chick embryo mitochondria to be a nucleic acid-containing structure, and its variable appearance after different fixations parallels that previously reported, or described in this paper, for the nucleoplasm of bacteria and blue-green algae. The results, in addition to those described in the accompanying communication, indicate that these mitochondria contain DNA.
INTRAMITOCHONDRIAL FIBERS WITH DNA CHARACTERISTICS
Authors: Nass Sylvan , Nass Margit M. K.
Published: May 2004

The effects of proteolytic enzymes, ribonuclease, and deoxyribonuclease upon a fibrous component of chick embryo mitochondria, which was previously shown to have many fixation and staining properties characteristic of the bacterial nucleoplasm, are reported. Pepsin digestion of formaldehyde-fixed tissues removed the membranes and matrices of mitochondria, but a pepsin-resistant fibrous material remained which was heavily stained by uranyl and lead ions. Experiments on a DNA "model system" showed that DNA treated with osmium tetroxide can be depolymerized by deoxyribonuclease. Zinc ions strongly inhibited the depolymerization of DNA. Digestion of osmium tetroxide-fixed tissues (fixed only briefly) with deoxyribonuclease for 1 hour greatly reduced the Feulgen staining of the nuclei, and after 4 hours the Feulgen reaction was completely abolished. The reduction and the disappearance of the Feulgen reaction in nuclei was paralleled by partial to complete digestion of the mitochondrial fibers in the regions studied (after 1 and 4 hours, respectively), without any other obvious changes in cellular structures. When deoxyribonuclease was inhibited by the addition of zinc ions, the nuclear Feulgen reaction was not diminished, nor were the mitochondrial fibers removed. Buffer control incubations for deoxyribonuclease and ribonuclease did not alter the structure or staining properties of the mitochondrial fibers, nor did incubation with ribonuclease. The latter reaction digested the cytoplasmic and nucleolar ribosomes after a 4-hour incubation period, in parallel with the abolishment of toluidine blue staining. The results contribute further evidence that these mitochondria contain deoxyribonucleic acid.
CENTRIFUGAL, BIOCHEMICAL, AND ELECTRON MICROSCOPIC ANALYSIS OF CYTOPLASMIC PARTICULATES IN LIVER HOMOGENATES
Authors: Kuff Edward L. , Hogeboom George H. , Dalton Albert J.
Published: May 2004

A combined centrifugal, biochemical, and electron microscopic study of the cytoplasmic particulates present in 0.88 M sucrose homogenates of rat liver has been carried out. Size distribution analyses of particles containing pentose nucleic acid (PNA) and exhibiting several types of enzymatic activity revealed three major size groups within the range of particle radius between 10 and 500 mµ. A different array of biochemical properties was associated with each size group. The largest particles, with an average radius (assuming spherical shape) in the region of 220 to 260 mµ, contained all of the succinic dehydrogenase activity of the cytoplasmic extract, 29 per cent of the diphosphopyridine nucleotide (DPN)-cytochrome c reductase activity, and minor amounts of PNA and acid phosphatase activity. Cytologically, this group of particles was identified with the mitochondria. All of the uricase activity, 58 per cent of the acid phosphatase activity, and 26 per cent of the PNA was apparently associated with a second size group of particles (average radius 120 mµ) which were tentatively identified by electron microscopy with vesicular structures derived from the ergastoplasm of the intact cell. The third particle group demonstrated by centrifugation exhibited a major size distribution peak at 25 mµ and a second smaller peak at 55 mµ. Over 50 per cent of the total cytoplasmic PNA and DPN-cytochrome c reductase activity was associated with particles in this size group. Electron microscopy revealed a morphologically heterogeneous population of particles within this size range.
THE STRUCTURE OF ACTIN-RICH FILAMENTS OF MUSCLES ACCORDING TO X-RAY DIFFRACTION
Authors: Selby Cecily Cannan , Bear Richard S.
Published: May 2004

From analysis of moderate- to small-angle x-ray diffraction patterns, in the light of similar experience with paramyosin, has been derived the following description for the structure of actin-rich filaments in "tinted" portions of the adductor muscle of the clam, Venus mercenaria:

1. Some 11 diffraction maxima, widely streaked along layer lines and occurring at moderate diffraction angles (spacings 7 to 60 A) appear to be accounted for as (hk) reflections of a net whose cell elements are, for dry material: a ≑ 82 A, b = 406 A (filament axis identity period), and γ ≑ 82° (angle between a and b axes). These reflections follow a selection rule which indicates that the net cell is non-primitive and contains 15 equivalent locations (nodes) arranged as shown in Fig. 5. An alternative net has b' = 351 A and 13 nodes per cell.

2. Another interpretation rolls the net into a large-scale helix and places the 15 (or 13) nodes along 7 (or 6) turns of a helical locus projecting 406 (or 351) A along the filament axis. Whether considered to be built of planar-net or helix-net cells, the individual filament contains a single cell width transverse to its axis. Transverse filament dimensions are, therefore, in either case similar (50 to 100 A).

3. Consideration of existing electron-optical, physicochemical, and x-ray diffraction data regarding isolated actin suggests that the net cell is built of rods, each containing in cross-section from one to four actin molecules which run parallel to or twisted about rod axes that extend at 12° to the filament axis along the (21) diagonals of the cell. Depending on monomer shape, 2 to 15 monomers furnish length to reach across two cells, and the actin molecules are built into each rod in such a way as to repeat (or nearly repeat) structure 15 (or 13) times along the double cell length. Further details of intra-rod structure cannot be suggested because of lack of wide-angle diffraction information.

4. The actin system is sensitive to treatment of the muscle with ethanol. Concentrations of 5 per cent or greater abolish the net reflections. Other solvents—water, benzene, ether, pyridine, acetone—do not alter the pattern materially.

5. Two other reflections, occurring at the first and second layer lines of an axial periodicity of about 400 A, do not clearly belong to the actin-net system. They represent either a superstructure built upon the filaments by parts of the actin molecules themselves or by incorporated other molecular species, or they arise from an additional macromolecular component (possibly myosin, or its homologues or fractions) of similar axial periodicity.
THE CYTOCHEMICAL LOCALIZATION OF ASCORBIC ACID IN ROOT TIP CELLS
Authors: Jensen William A. , Kavaljian Leroy G.
Published: May 2004

The intracellular distribution of ascorbic acid was studied in frozen-dried root tips of Allium cepa and Vicia faba by the silver nitrate procedure. The sites of the ascorbic acid as indicated by the deposited silver appear as spherical (0.2 to 0.6 µ in diameter) cytoplasmic particles. The site appears to have small amounts of lipides and to be rich in ribonucleic acid. These particles are concluded to be submicroscopic in size and associated, in the elongating cell, with the cell surface. In the meristematic cells they appear fewer in number and are distributed throughout the cytoplasm.
ELECTRON MICROSCOPY OF BASOPHILIC STRUCTURES OF SOME INVERTEBRATE OOCYTES
Authors: Rebhun Lionel I.
Published: May 2004

Highly basophilic plate-shaped regions from oocytes of the surf clam have been examined with the electron microscope. The regions are composed of flat, hollow vesicles perforated by pores arranged, in surface view, in a hexagonal pattern. Cross-sections of this structure show a periodicity consisting of loops (cross-sections of the continuous space within the vesicle) alternating with spaces partly filled with dense material (pores). These structures are shown to resemble closely, the nuclear envelope.

Similarities to and differences from basophilic regions of other cells are discussed and it is suggested that the small granules of Palade (38) are represented by granules composing the walls of the annuli of the nuclear envelope and assumed to be present in the annuli of the vesicles. Because of differences in the structure of these regions from basophilic regions of other cells, the name periodic lamellae is suggested since the structures show periodically repeating substructures (annuli) in both cross-sections and surface views.
A COMPARISON OF NUCLEAR DRY WEIGHTS DETERMINED BY CHEMICAL AND BY INTERFEROMETRIC METHODS
Authors: Hale Arthur J. , Kay Ernest R. M.
Published: May 2004

1. The nuclei of cells from the thymus of the calf were isolated by three different techniques; the citric acid, the sucrose-calcium chloride, and the non-aqueous.

2. The mean dry weights of the nuclei were determined by chemical methods and by microscopic interferometry. There was a close correlation between the results from the interferometric and chemical methods.

3. The range of values about that mean was determined in each sample: the nuclei isolated in aqueous media contained approximately 45 per cent less material than those isolated in non-aqueous media.

4. The variations in dry weight with varying nuclear type are discussed.

5. The possible relationship between DNA content and dry weight is discussed.
ELECTRON MICROSCOPY OF BASOPHILIC STRUCTURES OF SOME INVERTEBRATE OOCYTES
Authors: Rebhun Lionel I.
Published: May 2004

RNA containing yolk nuclei from the surf clam Spisula solidissima have been studied with the light microscope and with the electron microscope. A variety of structures can be seen with both and a correlation can be made between bodies studied with the electron microscope and those studied with the light microscope. The electron microscope shows many of these structures to be composed of double walled lamellae arranged in space, in various ways. The variety of patterns seen with the electron microscope can be satisfactorily explained on the basis of a hypothetical model. The presence of yolk platelets within the yolk nuclei lends support to classical observations on the synthesis of yolk within yolk nuclei or yolk nuclei derivatives. Small granules (about 100 A) are included within the double walled lamellae and their presence probably accounts for the basophilic nature of the entire body. The presence of small granules attached to electron-dense layers relates the yolk nuclei described here to ergastoplasm discussed by others.
LIVER MICROSOMES
Authors: Palade G. E. , Siekevitz P.
Published: May 2004

Rat liver, liver homogenates, and microsome fractions separated therefrom were examined systematically in the electron microscope in sections of OsO4-fixed, methacrylate-embedded tissue and pellets.

It was found that most microsomes are morphologically identical with the rough surfaced elements of the endoplasmic reticula of hepatic cells. They appear as isolated, membrane-bound vesicles, tubules, and cisternae which contain an apparently homogeneous material of noticeable density, and bear small, dense particles (100 to 150 A) attached to their outer aspect. In solutions of various osmolar concentrations they behave like osmometers. The findings suggest that they derive from the endoplasmic reticulum by a generalized pinching-off process rather than by mechanical fragmentation.

The microsome fractions contain in addition relatively few vesicles free of attached particles, probably derived from the smooth surfaced parts of the endoplasmic reticula. Dense, peribiliary bodies represent a minor component of the same fractions.

The microsomes derived from 1 gm. wet weight liver pulp contained (averages of 10 experiments) 3.09 mg. protein N, 3.46 mg. RNA (RNA/protein N = 1.12), and 487 µg. phospholipide P. They displayed DPNH-cytochrome c reductase activity and contained an alcohol-soluble hemochromogen.

The microsome preparations proved resistant to washing and "aging." Treatment with versene and incubation with ribonuclease (30 minutes at 37°C.) resulted in appreciable losses of RNA and in partial or total disappearance of attached particles.

Treatment with deoxycholate (0.3 to 0.5 per cent, pH = 7.5) induced a partial clarification of the microsome suspensions which, upon centrifugation, yielded a small pellet of conglomerated small, dense particles (100 to 150 A) with only occasionally interspersed vesicles. The pellet contained ∼80 to 90 per cent of the RNA and ∼20 per cent of the protein N of the original microsomes. The supernatant accounted satisfactorily for the materials lost during deoxycholate treatment.

The findings suggest that the microsomal RNA is associated with the small particles whereas most of the protein and nearly all of the phospholipide, hemochromogen, and DPNH-cytochrome c reductase activity are associated with the membrane or content of the microsomes.
MORPHOLOGICAL AND CYTOCHEMICAL IDENTIFICATION OF THE GOLGI APPARATUS
Authors: Chu C. H. U. , Swinyard C. A.
Published: May 2004

1. A modification of Elftman's direct silver method reveals both the lipochondria of Baker and the network of Golgi in the same cell. For purpose of distinction, it is proposed to call Baker's lipochondria the nucleopetal fraction, the Golgi network the nucleofugal fraction of the Golgi apparatus.

2. The nucleopetal fraction is located closer to the nucleus. It is spherical in shape and appears black in color. The nucleofugal fraction is located farther away from the nucleus. It is reticular in form and appears brown in color after silver impregnation by the modified Elftman's method.

3. These two fractions are separate entities. The network of Golgi is not due to deposition of silver on lipochondria. Lipochondria do not represent Golgi apparatus in living cells.

4. Aldehydes facilitate the demonstration of the nucleofugal fraction. Based on the circumstantial evidence presented, it appears that aldehyde dehydrogenase composed of a specific protein bound to a prosthetic group of flavin-adenine dinucleotide may be concentrated in this fraction.

5. Aldehyde dehydrogenase also functions as xanthine oxidase. It is suggested as a working hypothesis that under physiological condition, one of the functions of the nucleofugal fraction (Golgi network) is concerned with purine metabolism of nucleoproteins.
OXIDATIVE PHOSPHORYLATION IN MITOCHONDRIA FROM LIVERS SHOWING CLOUDY SWELLING
Authors: Fonnesu Alberto , Severi Clara
Published: May 2004

Using succinate and α-ketoglutarate as substrates, oxidative phosphorylation has been measured in mitochondria isolated from livers showing cloudy swelling. This cellular change was obtained by injecting rats with S. typhi murium toxin and guinea pigs with diphtheria toxin. It has been found that phosphorylation associated with the oxidation of either of these substrates was partially inhibited in mitochondria from livers showing cloudy swelling, while the oxygen consumption was unchanged. Thus, the P:O ratios for both succinate and α-ketoglutarate were lower in mitochondria from treated animals than they were in normal mitochondria. Dephosphorylation of ATP was not significantly modified in mitochondria from livers showing cloudy swelling as compared with normal controls. No dephosphorylation of AMP and G-6-P was observed either in normal mitochondria or in mitochondria from treated animals.
ELECTRON MICROSCOPE OBSERVATIONS ON SYNAPTIC VESICLES IN SYNAPSES OF THE RETINAL RODS AND CONES
Authors: De Robertis Eduardo , Franchi Carlos M.
Published: May 2004

The submicroscopic organization of the rod and cone synapses of the albino rabbit has been investigated with the use of the electron microscope. The most common rod synapse consists of an enlarged expansion of the rod fiber (the so called spherule) into which the dendritic postsynaptic fiber of the bipolar cell penetrates and digitates. The membrane surrounding the terminal consists of a double layer, the external of which is interpreted as belonging to the intervening glial cells. The synaptic membrane has a pre- and a postsynaptic layer with a total thickness of 180 to 300 A. The presynaptic layer is frequently denser and is intimately associated with the adjacent synaptic vesicles. The synaptic membrane shows processes constituted by foldings of the presynaptic layer. The entire spherule is filled with synaptic vesicles varying in diameter between 200 and 650 A with a mean of 386 A. In addition, the spherule contains a few large vacuoles near the rod fiber, interpreted as endoplasmic reticulum, and a matrix in which with high resolution a fine filamentous material can be observed. The postsynaptic fiber is homogeneous and usually does not show synaptic vesicles.

In animals maintained in complete darkness for 24 hours vesicles appear to accumulate near the synaptic membrane and its processes. After 9 days there is a sharp decrease in size of the synaptic vesicles.

A special rod synapse in which the dendritic postsynaptic expansion penetrates directly into the rod cell body has been identified. In line with Cajal's classification this type of synapse could be considered as a somatodendritic one.

The cone synapse has a much larger terminal with a more complex relationship with the postsynaptic fiber. However, the same components recognized in the rod synapse can be observed. In animals maintained for 9 days in complete darkness there is also a considerable diminution in size of the synaptic vesicles.
ELECTRON MICROSCOPE OBSERVATIONS ON THE SUBMICROSCOPIC ORGANIZATION OF THE RETINAL RODS
Authors: De Robertis Eduardo
Published: May 2004

The submicroscopic organization of the retinal rods of the rabbit has been studied with high resolution electron microscopy in thin longitudinal and cross-sections. The outer rod segment consists of a stack of flattened sacs or cisternae each of them limited by a thin homogeneous membrane of about 30 A. The membrane of the rod sacs is attached to the surface membrane and is also in continuity with short tubular stalks of about 100 to 150 A which apparently end in relation with the connecting cilium.

The bundle of filaments that constitute the connection between the outer and the inner segments is described under the name of connecting cilium. This fibrous component has a structure that is very similar to that of the cilium. It shows 9 pairs of peripheral filaments of about 160 A in diameter, a matrix material, and a surface membrane. Very infrequently two central single filaments are observed. The connecting cilium has a typical basal body in the inner segment; its distal end penetrates the outer segment, where it establishes some structural relation to the rod sacs. The relationships and submicroscopic organization of the connecting cilium were studied in longitudinal and in cross-sections passing at different levels of the rod segments.

The inner rod segment shows two distinct regions: a distal and a proximal one. The distal region, corresponding to the ellipsoid of classical histology is mainly composed of longitudinally packed mitochondria. It also contains the basal body of the cilium, vacuoles of the endoplasmic reticulum, dense particles, and intervening matrix with very fine filaments.

In the proximal region of the inner segment the mitochondria are lacking and within the matrix it is possible to recognize elements of the Golgi complex, vacuoles of the endoplasmic reticulum, dense particles and numerous neuroprotofibrils of 160 to 200 A in diameter which collect and form a definite bundle at the exit of the rod fiber.

The interpretation of the connecting fibers as a portion of a cilium and of the outer segment as a differentiation of the distal part of a primitive cilium are discussed. The importance of the continuity of the surface membranes of the outer segment, connecting cilium, and inner segment is emphasized and its possible physiological role is discussed.
STRUCTURE AND DEVELOPMENT OF VIRUSES OBSERVED IN THE ELECTRON MICROSCOPE
Authors: Morgan Councilman , Howe Calderon , Rose Harry M. , Moore Dan H.
Published: May 2004

Representative viruses of the RI-APC group were observed with the electron microscope in thin sections of infected HeLa cells. The viral particles varied in density, were approximately 60 mµ in diameter and had a center to center spacing when close packed of about 65 mµ. Many of the less dense particles exhibited an internal body averaging 24 mµ in diameter. It was suggested that within the nucleus the virus differentiated from dense granular and reticular material and formed crystals. Disintegration of the crystals and disruption of the nuclear membrane with release of virus into the cytoplasm appeared to occur at any stage. No evidence to suggest development of the virus in the cytoplasm was obtained.

It was possible to deduce the structure of the viral crystal from the electron micrographs. The viral particles are packed in a cubic body—centered lattice.

Correlative histochemical observations in the light microscope which are now in progress revealed that the crystals and non-crystalline aggregates of virus were strongly Feulgen-positive.
THE FINE STRUCTURE OF STRIATED MUSCLE
Authors: Hodge A. J.
Published: May 2004

The available evidence from phase contrast, polarization optical, and electron microscopic studies on vertebrate skeletal muscle, insect skeletal muscle, and dipteran flight muscle is interpreted as favoring the following general structure of striated muscle.

A continuous array of filaments (actin) runs through all bands of the sarcomere. These are linked by an axially periodic system of transverse filamentous bridges. Myosin (and probably other substances) are localized in the A bands. The system of transverse bridges compensates the birefringence of actin and is thus responsible for the isotropy of the I band. Myosin is responsible for the birefringence of the A bands. On strong contraction, A band material migrates to the Z bands to form contraction bands. It is not yet certain whether this migration involves myosin or another A band component.
COMPARATIVE CYTOPHYSIOLOGY OF STRIATED MUSCLE WITH SPECIAL REFERENCE TO THE ROLE OF THE ENDOPLASMIC RETICULUM
Authors: Edwards George A. , Ruska Helmut , de Souza Santos Persio , Vallejo-Freire Aristides
Published: May 2004

1. The structure and distribution of the components of striated muscle cells vary with the species and with the specialization of muscle fiber function.

2. There appear to be two, easily distinguishable, general categories of striated muscle structure.

A. High frequency muscle (represented by flight muscle of higher insects and hummingbird, and cicada tympanal muscle) is characterized by widely spaced, non-branching fibrils of large diameter and short period, little endoplasmic reticulum, and large quantities of large mitochondria (low fibril-sarcoplasm ratio). This structure is correlated with heavy tracheolization or vascularization, high oxidative activity, and dark color as compared with other muscles of the same species.

B. Low frequency muscle is characterized, in general, by high fibril-sarcoplasm ratio, relatively long period, few mitochondria increasing with activity and decreasing with absolute power of the fiber. Oxidative capacity and color are proportional to the quantity of mitochondria. These fibers are further differentiated into (a) fibrillar arrangement of contractile material which permits a regular pattern of interfibrillar and segmental reticulum, and (b) afibrillar arrangement of contractile material leading to an unsystematic distribution of reticulum.

3. The endoplasmic reticulum appears as a complex coordination system in the muscle fiber. Peripherally, it links the Z and M lines of the fibrils to the sarcolemma and between the fibrils it links the cross-bands, forming the Grundmembran of earlier authors. By longitudinal linkage, it connects with the sarcolemma at the muscle extremity to form a digital arrangement into which the tendon fibrils are spliced. The extent of its development and its position have a definite relationship to the degree and site of fiber shortening. At present the reticulum is the only structure that one can consider to be an internal conducting system. It may distribute the excitation transversely from fibril to fibril, and lengthwise saltatorially to the symmetry centers of the sarcomeres.

4. The nucleus is the mediating element between the cytoplasmic phases within and without the tubular system of the endoplasmic reticulum. A possible mechanism which correlates nucleus, adenylic acid system, ion exchange, and reticulum with the initiation of contraction is postulated.
SYNAPSES IN THE CENTRAL NERVOUS SYSTEM
Authors: Palay Sanford L.
Published: May 2004

A number of different synapses have been described in the medulla, cerebellar cortex, and cerebral cortex of the rat. All of these possess the same fundamental fine structure as follows:

1. Close apposition of the limiting membranes of presynaptic and postsynaptic cells without any protoplasmic continuity across the synapse. The two apposed membranes are separated by a cleft about 200 A wide, and display localized regions of thickening and increased density.

2. The presynaptic expansion of the axon, the end-foot or bouton terminal, contains a collection of mitochondria and clusters of small vesicles about 200 to 650 A in diameter.

Although the significance of these structures in the physiology of the synapse is still unknown, two suggestions are made: that the mitochondria, by means of the relation between their enzymatic activity and ion transport, participate in the electrical phenomena about the synapse; and that the small synaptic vesicles provide the morphological representation of the prejunctional, subcellular units of neurohumoral discharge at the synapse demanded by physiological evidence.
MORPHOGENESIS OF THE RETINAL RODS
Authors: De Robertis E.
Published: May 2004

The morphogenesis of the retinal rods has been studied with the electron microscope in white mice from birth up to the 16th day of age. Observations have been mainly concentrated on specimens of the 8th and 12th days and on the differentiation of the inner and outer segments of the retinal rods. In the morphogenesis of the outer segment three main stages have been considered.

The first stage consists in the development of a primitive cilium projecting from a bulge of protoplasm which constitutes the primordium of the inner segment. A basal body, nine pairs of peripheral filaments, a surface membrane, and a matrix filled with a fine vesicular material have been recognized as components of the primitive cilium. The vesicles are called "morphogenetic material" because it is believed that they represent the macromolecular primordium of the rod sacs of the future outer segment.

The second stage corresponds to the great enlargment of the apical region of the primitive cilium due to the rapid building up of the lamellar material of the rod sacs. The primitive rod sacs appear to be connected with the ciliary filaments. The basal portion of the primitive cilium remains undifferentiated and constitutes the connecting cilium of the adult rod (1).

The third stage consists in the remodelling and reorientation of the rod sacs into their permanent transverse disposition. This process starts in the middle portion of the outer segments and proceeds towards both extremities which can be considered as zones of growth of the outer segment.

The inner segment is at the beginning a bulge of protoplasm containing unoriented mitochondria, a basal body, a small Golgi zone, and numerous dense particles. Then this region becomes elongated and the different components assume the stratified disposition found in the adult (1).

The demonstration that the entire outer segment of the rod cell is the result of the differentiation of a primitive cilium is discussed in view of the conflicting interpretations found in the literature.

The possible macromolecular mechanisms that may be involved in the submicroscopic morphogenesis of the rod sacs are discussed and the possible role of the morphogenetic material is considered.

The results described in this paper confirm and extend the interpretation of the submicroscopic morphology of the adult rod cell as presented in a previous paper (1).
EFFECTS OF THE PHYSICAL ENVIRONMENT ON SOME LIPOPROTEIN LAYER SYSTEMS AND OBSERVATIONS ON THEIR MORPHOGENESIS
Authors: Hodge A. J.
Published: May 2004

Lipoprotein membrane systems such as chloroplasts and the endoplasmic reticulum exhibit a generalized swelling response. The initial effect is an increase in interlamellar spacing, but as swelling proceeds, the membranes are transformed into closed thin-walled spherical vesicles.

Available evidence suggests that morphogenesis of the endoplasmic reticulum of Nitella and the lamellar system of the Zea chloroplasts involves fusion of small spherical vesicles to yield closed double membrane structures, which subsequently undergo further differentiation.

It is suggested that the vesicles comprise a convenient "micellar" form by which lipides may be transported within the cell from the sites of lipide synthesis to regions of lamellar growth. The characteristic formation of vesicles in swelling and the apparent fusion of vesicles in morphogenesis appear to represent two aspects of a fundamental plasticity of lipoprotein layer systems.
THE BASEMENT LAMELLA OF AMPHIBIAN SKIN
Authors: Weiss Paul , Ferris Wayne
Published: May 2004

The basement lamella under the epidermis of amphibian larvae shows a sub-microscopic architecture of remarkable geometric regularity: It consists of about twenty layers of ground substance in which cylindrical fibers (presumably collagenous) of about 500 Angström diameter are embedded parallel to one another, but with the fiber directions alternating by 90° from layer to layer. The repair of this membrane after wounding was studied electronmicroscopically in ultrathin sections. The sequence of events is as follows: (1) Epidermal cells cover the wound exudate by migration. (2) Rather uniform fibers of small size (<200 A) appear in the space between the epidermal underside and the subjacent fibroblasts; these fibers are sparse and oriented at random. (3) Proceeding from the epidermal surface downward, a wave of organization spreads over this primitive fiber tangle, resulting in the fibers becoming (a) straightened; (b) oriented; (c) packed into the characteristic layered structure; and (d) brought up into the 500 A diameter class.