Biomedical subjects
R A Lewin
Publications and source records attributed to R A Lewin.
More on Merde.
Whereas food has always received much attention in conversation, commerce, and the literature, the subject of feces has been comparatively neglected. To fill this lacuna, a small book on comparative coprology was recently published (Lewin 1999). The present article aims to supplement this book with a review of overlooked or new items relating to biological and medical aspects of coprology, notably chemical and microbial components of human and animal feces, their uses as fertilizers, and a few other sociological impacts.
Boundaries in clinical psychiatry.
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On chronic suicidality.
Chronically suicidal patients with serious personality disorders present their therapists with clinical problems that are subtle, intense and complicated. Therapists need to tolerate a great deal of uncertainty, to recognize both the interpersonal and the intrapsychic complexities of the functions and meanings of suicidality, and, above all, to keep in view the fact that the suicidality is both a hindrance and a help to the patient. Suicidality, in fact, may be central to a patient's search for a degree of dignity and autonomy as well as connectedness worth staying alive to enjoy.
Characterization of gliding motility in Flexibacter polymorphus.
Motility of the marine gliding bacterium Flexibacter polymorphus was studied by using microcinematographic techniques. Following adhesion to a glass surface, multicellular filaments and individual cells usually began to glide within a few seconds at a speed of approximately 12 micron per second (at 23 degrees C). Adhesion to the glass surface was evidently mediated by multitudes of extremely fine extracellular fibrils. Gliding velocity was independent of filament length but directly related to electron-transport activity and substratum temperature in the range 3-35 degrees C. The rate of gliding was inversely related to medium viscosity, suggesting that the locomotor apparatus functions at constant torque. Forward motion was occasionally interrupted by direction reversals, somersaults (observed primarily in single cells of short filaments), or spinning of filaments tethered by one pole. The frequency of direction reversal was found to be an inverse function of filament length. Translational motility was invariably accompanied by sinistral revolution about the longitudinal axis of a filament. The sense and pitch of revolution were constant among filaments of different length. Polystyrene microspheres or India ink particles adsorbed to gliding cells were actively displaced in either direction, their movement tracing either a regular zigzag or helical path along the filament surface. Because microspheres were also observed to move on nonmotile filaments, particle translocation was evidently not obligatorily linked to gliding locomotion. Multiple particles adsorbed to a single filament often moved independently. The data are consistent with a motility mechanism involving limited motion in numerous mechanically independent (yet functionally coordinated) domains on the cell surface.
A mental health worker's vocation.
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Prochloron--a status report.
Prochloron is a genus of prokaryotic algae with photosynthetic pigments like those of chlorophytes. Prochlorophytes are almost invariably found associated as symbionts with marine protochordates (didemnid ascidians), and so far none has been successfully grown in sustained culture away from in host. Based on materials collected from nature, information of various sorts (biochemical, physiological, cytological and fine-structural) has been obtained, indicating many resemblances (and probably close phylogenetic affinities) between prochlorophytes and cyanophytes. Nevertheless they are distinguished by certain unique combinations of characters. Some of the data support the symbiogenesis theory for the origin of green-plant chloroplasts. Other possibilities are briefly discussed.
Subunit composition of goblet-shaped particles from the cell wall of Flexibacter polymorphus.
Submicroscopic goblet-shaped particles ( goblets ) were released from the cell envelope of the marine gliding bacterium Flexibacter polymorphus when treated with the nonionic detergent Triton X-100 followed by sonication. The goblets were purified by cesium chloride density gradient centrifugation and exhibited an equilibrium buoyant density of 1.30 g/mL at 23 degrees C. They were composed of protein and a small amount of carbohydrate (approximately 3.4% by weight). Aqueous suspensions exhibited an absorption maximum in the ultraviolet at a wavelength of 276 nm and a smaller shoulder at 281 nm. Phospholipids were not detected in purified preparations of goblets , though they are known to be prominent constituents of the intact membranes of this microbe. Polyacrylamide gel electrophoresis of goblets solubilized in sodium dodecyl sulfate and 2-mercaptoethanol indicated four major polypeptide components ranging in molecular weight from 13 000 to 80 000. This number of different protein subunits corroborates earlier ultrastructural observations indicating a multisubunit composition.
Effects of various agents on flagellar activity, flagellar autotomy and cell viability in four species of Chlamydomonas (chlorophyta: volvocales).
Over 200 strains of green algal flagellates, representing about 100 species, were examined for their suitability as experimental organisms for studies of flagellar activity. The cells of all species shed their flagella under unfavourable conditions of temperature or pH, or in the presence of alcohols, detergents or toxic agents of various kinds. For further studies of flagellar activity, motility and autotomy (biologically induced shedding) in particular, we selected four species of Chlamydomonas: C. dysosmos Moewus, C. moewusii Gerloff, C. monoica Strehlow and C. reinhardtii Dangeard. Agents found to inhibit motility without inducing death or flagellar autotomy included azide, arsenite, thiosulphate, cyanide, ferricyanide, hydroxylamine, chloral hydrate, malonate, p-chloro-mercury benzoate and cytochalasin-B, each in a limited range of concentrations which differed according to species and strain. Higher concentrations of these agents caused the flagella to be shed. Since flagellar autotomy is a means by which a cell can quickly reduce the area of its permeable surface, it may have a positive survival value for species liable to be subjected to unfavourable physicochemical conditions.
Prochloron and the theory of symbiogenesis.
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The greening of polar bears in zoos.
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Polonium and plutonium in an intertidal food chain.
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Prochlorophyta as a proposed new division of algae.
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Lead uptake in two marine phytoplankton organisms.
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Fine structure of the cell envelope layers of Flexibacter polymorphus.
Electron microscopy of the filamentous gliding marine bacterium Flexibacter polymorphus demonstrated that the cell envelope consists of an electron-dense intermediate layer located between two unit-type membranes: an outer membrane, presumably of lipopolysaccharide, and an inner cytoplasmic membrane. Separation of living filaments into single cells by lysozyme suggests that a peptidoglycan moiety, possibly corresponding to the intermediate layer, might be situated between the two membranes. Cell division proceeds by invagination of the cytoplasmic membrane and intermediate layer forming a transverse septum. Cells generally fail to separate after the division process, so that a common outer membrane encloses all of the cells in a single filament. There is a continuous layer of macromolecular cup-shaped elements ('goblets') attached to the outermost surface of the lipopolysaccharide membrane. Tangential thin sections, as well as negatively stained preparations of envelope fragments (produced by sonication of autolyzed cells), showed that the goblets are arranged in a close-packed hexagonal array. The presence of electron-dense structures located between the outer and inner membranes, and exhibiting the same periodicity as the goblets, suggests that some part of the goblets penetrates the outer membrane and extends across the periplasmic space to the dense intermediate layer or cytoplasmic membrane. Spontaneous autolysis in aging cultures is accompanied by the formation and release into the culture medium of large numbers of outer membrane vesicles coated with globlets. A tentative reconstruction of the envelope of F. polymorphus, based on the fine-structural data, is presented.
Fluidisation as a feeding mechanism in beach flies.
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Pollution is a dirty word.
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Preservation of viable flexibacteria at low temperatures.
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