Showing papers by "University College London published in 1969"
TL;DR: The structure of the human, but mainly of the rhesus monkey, retina as examined by Golgi-staining techniques is described and interpreted on evidence from both light and electron microscopy.
Abstract: The structure of the human, but mainly of the rhesus monkey, retina as examined by Golgi-staining techniques is described and interpreted on evidence from both light and electron microscopy. One type of rod bipolar cell and two types of cone bipolar cell are recognized. The rod bipolar is exclusively connected to rods. The midget bipolar is postsynaptic to only one cone but each cone is also presynaptic to a diffuse cone (flat) bipolar. Such flat bipolar cells are in synaptic relationship with about seven cones. No other bipolar cell types have been found. The brush bipolar of Polyak is interpreted as probably a distorted rod bipolar, while Polyak's centrifugal bipolar is a misinterpretation of the morphology of diffuse amacrine cells. When presumptive centrifugal bipolars were observed they appeared to be a developmental stage of amacrine cells. In the outer plexiform layer two types of horizontal cell have been defined. Each type of horizontal cell has a single axon and two kinds of horizontal cell axon terminals are recognized. In the inner plexiform layer there are two main classes of amacrine cells: the stratified amacrines and the diffuse amacrines. Each class of amacrine has a wide variety of shapes. Polyak's midget ganglion cell is confirmed and his five other kinds of ganglion cell are classified into diffuse and stratified ganglion cells according to the level at which their dendrites branch within the inner plexiform layer. A fuller summary is given by the diagram and in the legend of figure 98, p. 174. A new type of midget bipolar is described in the Appendix (p. 177).
552 citations
525 citations
TL;DR: In this paper, a rational theory is developed to explain the initial pressure rise and consequent separation of a laminar boundary layer when it interacts with a moderately strong shock, where the region of interest is divided into three parts: the major part of the boundary layer, which is shown to change under largely inviscid forces, the supersonic main stream just adjacent to the boundary surface, and a region close to the wall, on boundary-layer scale, in which the relative variation of the velocity is controlled by the incompressible boundary layer equations.
Abstract: A rational theory is developed to explain the initial pressure rise and consequent separation of a laminar boundary layer when it interacts with a moderately strong shock. In this theory, which is firmly based on the linearized theory of Lighthill (1953), the region of interest is divided into three parts: the major part of the boundary layer, which is shown to change under largely inviscid forces, the supersonic main stream just adjacent to the boundary layer in which the pressure variation is small; and a region close to the wall, on boundary-layer scale, in which the relative variation of the velocity is large but is controlled by the incompressible boundary-layer equations, together with novel boundary conditions. We find that the first two parts can be handled in a straightforward way and the problem of self-induced separation reduces, in its essentials, to the solution of a single problem in the theory of incompressible boundary layers. It is found that this problem has three solutions, one of which corresponds to undisturbed flow and another describes a boundary layer which, spontaneously, generates an adverse pressure gradient and a decreasing skin friction which eventually vanishes and then downstream a reversed flow is set up. The third solution generates a favourable pressure gradient and is not relevant to the present study. Although there has hitherto been no valid numerical method of integrating a boundary layer with reversed flow, we find that an ad hoc method seems to lead to a stable solution which has a number of the properties to be expected of a separated boundary layer. Comparison with experiment gives qualitatively good agreement, but quantitatively errors of the order of 20% are found. It is believed that these errors arise because the Reynolds numbers at which the experiments were carried out are too small.
504 citations
TL;DR: It is suggested that the coat in bloodstream trypanosomes constitutes a replaceable surface which, after being replaced, enables thetrypanosome to escape the effects of host antibodies.
Abstract: Pathogenic trypanosomes in their bloodstream phase have a smooth and compact coat 12-15 nm thick enveloping the entire surface membrane of the body and flagellum. In the sleeping-sickness trypanosome Trypanosoma rhodesiense this coat is absent from the stages of development in the midgut of the tsetse-fly vector and from their counterparts obtained by cultivation of the trypanosome in vitro. In the salivary glands of the vector, however, the coat is reacquired as the trypanosomes transform from epimastigote forms into the metacyclic stage which is infective to the mammalian host. This loss and acquisition of the surface coat can be correlated with the cyclical changes in net surface charge on the trypanosome which have been observed by other workers. The trypanosome populations of successive relapses in the blood are known to differ in their surface antigens (agglutinogens) and the loss of antigenic identity detected when any of these populations are put into culture indicates that these variable antigens are located in the surface coat. It is suggested that the coat in bloodstream trypanosomes constitutes a replaceable surface which, after being replaced, enables the trypanosome to escape the effects of host antibodies. The coat is therefore an adaptation to life in the bloodstream. Reacquisition of the surface coat by the metacyclic trypanosome after development in the vector may reflect reversion to a ‘basic’ antigenic type at this stage, preparatory to invading the blood of the mammalian host. The surface coat may be removed by the wide-spectrum proteolytic enzyme pronase, and this fact together with evidence from pH/mobility relationships and chemical analysis of the variable antigens suggest that the coat is basically proteinaceous. The coat may facilitate pinocytosis by binding proteins at sites within the pocket surrounding the base of the flagellum. In the non-pathogenic trypanosome T. lewisi a more diffuse filamentous coat is present in bloodstream forms and absent from culture forms. This trypanosome is said to carry a negative charge in both bloodstream and culture phases, so it seems likely that the nature of the coat in T. lewisi is different from that found in the pathogenic trypanosomes. In all these trypanosomes the flagellar membrane adheres to the surface membrane of the body throughout the life-cycle. Along the zone of adhesion lies a regular row of junctional complexes of the macula adherens type which, it is argued, serve in attachment. These attachments persist regardless of changes in the intervening cell surfaces.
428 citations
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TL;DR: The ene reaction is defined as the indirect substituting addition of a compound with a double bond (enophile) to an olefin with an allylic hydrogen (ene) as discussed by the authors.
Abstract: The ene reaction is defined as the indirect substituting addition of a compound with a double bond (enophile) to an olefin with an allylic hydrogen (ene). For a long time the reaction has been neglected and has remained overshadowed by the related Diels-Alder addition. It is shown that the ene reaction possesses wide scope and applicability ranging from industrial to biosynthetic processes. Preparative aspects are summarized and current views on the mechanism are discussed.
396 citations
TL;DR: This paper was delivered as a lecture to the Conference of The Prehistoric Society on 'The Interpretation of Funerary Evidence' held in London on 2I-3 March 1969 and is essentially unchanged from the lecture delivered on that occasion except for the addition of references.
Abstract: (1969). Ethnography and archaeological interpretation of funerary remains. World Archaeology: Vol. 1, Techniques of chronology and excavation, pp. 262-280.
365 citations
TL;DR: Microtubules in the cytoplasm of a small amoeba are described, believed to be a new species of the genus Hartmannella.
Abstract: INVESTIGATIONS of a wide range of cells have shown that microtubules, acting as skeletal elements, are associated with cytoplasmic movements1–3 Here I describe microtubules in the cytoplasm of a small amoeba, believed to be a new species of the genus Hartmannella4
341 citations
TL;DR: The rationalization of scientific library systems might be greatly facilitated by the application of Bradford's law, formulated more than twenty years ago.
Abstract: The rationalization of scientific library systems might be greatly facilitated by the application of Bradford's law, formulated more than twenty years ago.
312 citations
TL;DR: In this paper, an analytically simple self-consistent description of the modes of a circular dielectric structure is presented, resulting in an asymptotic technique.
Abstract: An asymptotic technique is presented, resulting in an analytically simple self-consistent description of the modes of a circular dielectric structure. When the dielectric difference between the rod and surrounding medium is small, the asymptotic expressions are valid for all frequencies. Even when the inside dielectric constant is twice the outside, less than a 10 percent error is usually involved. A simple functional expression for the eigenvalues of both the circular rod and the dielectric slab results from the analysis, thus eliminating the need for numerical or graphical methods.
295 citations
TL;DR: Examination of cutaneous receptive fields of lamina 5 cells in the lumbar spinal cord of decerebrate cats shows them to have three distinct zones with respect to mechanical and electrical stimulation, consistent with a model in which high and low threshold fibres correspond approximately to the small and large diametre fibres whose balance is the basis for the coding of pain in the theory of melzack and wall.
Abstract: Examination of cutaneous receptive fields (RFs) of lamina 5 cells in the lumbar spinal cord of decerebrate cats shows them to have three distinct zones with respect to mechanical and electrical stimulation. The mean response rate to both mechanical and electrical stimulation in zone 1 increases steadily up to the highest strengths used; in zone 2, surrounding zone 1 mainly proximally, mild stimuli reduce the mean rate, stronger stimuli increase it; in zone 3, mainly proximal to zone 2, all stimuli reduce the rate.
274 citations
TL;DR: In the fish, CNS aldehyde fixation reveals a dramatic and easily distinguishable difference in axonal knobs with round and those with flat vesicle wall changes, which is possible to distinguish excitatory from inhibitory terminals, to a limited extent, simply on the difference of round orflat vesicles after alde Hyde fixation.
Abstract: Publisher Summary This chapter discusses three categories of morphological configurations of neuro-neuronal and neuro-muscular synapses: (1) nonserial cleft synapses, (2) nonserial synapses with tight junctions, and (3) serial synapses with no tight junctions. Initial fixation of the central nervous system (CNS) is done by perfusion with buffered aldehyde solutions, such as formaldehyde, glutaraldehyde, or a mixture of both. The treatment with aldehyde affects the vesicles containing excitor in one way and inhibitor in another. This may be caused by the tonicity changes or molecular changes in the vesicle wall or a combination of both due to the aldehyde reaction. It is possible to distinguish excitatory from inhibitory terminals, to a limited extent, simply on the difference of round or flat vesicles after aldehyde fixation. In the fish, CNS aldehyde fixation reveals a dramatic and easily distinguishable difference in axonal knobs with round and those with flat vesicles.
TL;DR: This paper contains further family data and more extensive population data on the ADA polymorphism and also a description of a new phenotype.
Abstract: In a study of human red cell adenosine deaminase (ADA) three different types of isozyme patterns were identified (Spencer, Hopkinson & Harris, 1968). One phenotype designated ADA 1 was found in about 89 % of the English population, the second phenotype, ADA 2-1, was found in about 11 yo of the population and the third phenotype, designated ADA 2, was seen only once in a survey of 580 unrelated English people. Sixty-seven families were studied and the family data suggested that the three ADA phenotypes were determined by two autosomal alleles ADA1 and ADA2; phenotypes ADA 1 and ADA 2 corresponding to the homozygous genotypes ADAlADAl and ADAaADA2 respectively and phenotype ADA 2-1 corresponding to the heterozygous combination ADA1ADA2. This paper contains further family data and more extensive population data on the ADA polymorphism and also a description of a new phenotype.
TL;DR: The effect of sympathomimetic amines on antigen-induced histamine release in passively sensitized human lung tissue is investigated and it is found that, in concentrations less than 1/1,000th of those of the most active inhibitors hitherto reported, they can prevent anaphylactic Histamine release.
Abstract: THE release of histamine after the application of antigen to a sensitized tissue provides a readily measurable index of the occurrence of a cellular anaphylactic reaction, while inhibition of the release in these conditions provides a measure of inhibition of the anaphylactic reaction. Various substances, including metabolic inhibitors, anaesthetics and antipyretics, have been found to inhibit anaphylactic histamine release1; their 50 per cent inhibitory concentrations vary from 2 × 10−5 M to 10−1 M (for example, in the actively sensitized guinea-pig lung it is 10−4 M for iodoacetate and 4 − 10−3 M for phenylbuta-zone). An early finding2 was that adrenaline, as well as inhibiting bronchoconstriction, prevents the release of histamine during the anaphylactic reaction of isolated guinea-pig lung. Large doses of adrenaline (1 rng injected into the perfusate) were used to obtain this effect. It has also been shown3 that isoprenaline inhibits antigen-induced histamine release from actively sensitized human leucocytes, with concentrations of 2–6 × 10−4 M required for 50 per cent inhibition. We have investigated the effect of sympathomimetic amines on antigen-induced histamine release in passively sensitized human lung tissue and found that, in concentrations less than 1/1,000th of those of the most active inhibitors hitherto reported, they can prevent anaphylactic histamine release.
TL;DR: Observations of fibroblasts by time lapse and still microphotography clarify the nature of the “ruffling” phenomenon, and suggest a mechanism for locomotion and contact inhibition.
Abstract: Observations of fibroblasts by time lapse and still microphotography clarify the nature of the “ruffling” phenomenon, and suggest a mechanism for locomotion and contact inhibition.
TL;DR: In this paper, a novel technique has been developed for measurement of dispersion and wavelength in microstrip transmission line laid down on an Al2O3 substrate, which can be satisfactorily used at far higher frequencies.
Abstract: A novel technique has been developed for measurement of dispersion and wavelength in microstrip transmission line laid down on an Al2O3 substrate. The frequency range so far investigated has been 4-12GHz, although the method could be satisfactorily used at far higher frequencies. The measurement accuracy is better than within 1%. Techniques for producing well matched transitions to any thickness substrate have also been established.
TL;DR: The results suggest either that Piaget's theory of ‘formal operations’ requires modification, or that some of the subjects may have temporarily regressed to more primitive modes of thinking.
Abstract: This investigation is concerned with the effects of two kinds of contradiction on the correction of errors in a structurally simple but deceptively difficult logical problem. The task was to choose from partially concealed material those stimuli which were necessary to evaluate the truth or falsity of a general statement. Hypothetical contradiction is assumed to occur when the subject makes an inference which is inconsistent with a previous incorrect choice. Concrete contradiction is assumed to occur when the subject's current choice is shown to be inconsistent with the fully revealed material. Of the 32 subjects, two were substantially correct in their initial choices, 14 were correct after encountering two hypothetical contradictions, 12 were correct after encountering a concrete contradiction, and four failed altogether. The results suggest either that Piaget's theory of ‘formal operations’ requires modification, or that some of the subjects may have temporarily regressed to more primitive modes of thinking.
TL;DR: In this paper, a quasi-optical expression for mode Iaunching on a semi-infinite rod was derived for small angles of incidence /spl theta/ = 0.
Abstract: A technique similar to that of Kirchhoff is used to obtain an analytic expression for mode Iaunching on a semi-infinite rod. The approximation is quasi-optical and only valid for small angles of incidence /spl theta/. When /spl theta/ = 0 only HE/sub 1M/ modes are excited; however, for /spl theta/<<1 many modes can be launched. The effect on HE/sub 11/ mode propagation of small imperfections in a dielectric waveguide is analyzed. At the frequency of interest for optical communication (cutoff for the TM/sub 01/ mode) the radiated power is 160 times larger than that scattered into the HE/sub 11/ mode.
TL;DR: Pigeons were trained on a two-link concurrent chain schedule in which responses on two keys were reinforced according to independent variable-interval schedules by the production of a change in key color.
Abstract: Pigeons were trained on a two-link concurrent chain schedule in which responses on two keys were reinforced according to independent variable-interval schedules by the production of a change in key color. Further responses on the key on which the stimulus change had been produced gave a single food reinforcement and a return to concurrent variable-interval conditions. On one key the terminal link was a two-valued mixed-interval schedule, while on the other, the terminal link was a fixed-interval schedule. When the mixed-interval values were kept constant and the fixed-interval values varied, relative response rates in the initial concurrent links matched relative reinforcement rates in the terminal links when these were computed from cubic transformations of the reciprocals of the intervals comprising the terminal link schedules.
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TL;DR: In this article, ausammenstellung der praparativen Aspekte folgte eine Diskussion des Reaktionsmechanismus, das das Anwendungsgebiet der En-Reaktion von industriellen bis zu biosynthetischen Prozessen reicht.
Abstract: Unter „En-Reaktionen” versteht man die indirekte substituierende Addition einer Verbindung mit Doppelbindung (Enophil) an ein Olefin mit allylischem Wasserstoff (En). Lange Zeit stand die En-Reaktion im Schatten der verwandten Diels-Alder-Addition. In diesem Aufsatz wird gezeigt, das das Anwendungsgebiet der En-Reaktion von industriellen bis zu biosynthetischen Prozessen reicht. Einer Zusammenstellung der praparativen Aspekte folgte eine Diskussion des Reaktionsmechanismus.
TL;DR: A technique for the short-term measurement of the rate of human ageing is now both necessary and possible and would offer a method of attacking the real possibility that drugs and environmental agents already current may affect that rate.
TL;DR: The fine structure of 2 isolates of Trypanosoma congolense maintained in laboratory rodents has been studied from thin sections of osmium- and aldehyde-fixed flagellates and it is suggested that the secretion is transported for discharge into the flageLLar pocket by way of multivesicular bodies and smooth-walled tubules or vesicles.
Abstract: SYNOPSIS. The fine structure of 2 isolates of Trypanosoma congolense maintained in laboratory rodents has been studied from thin sections of osmium- and aldehyde-fixed flagellates. The pellicular complex, nucleus, and flagellar apparatus are all similar to those of other African trypanosomes. Aberrant intracellular differentiation of the flagellum is occasionally found.
As in bloodstream forms of other salivarian trypanosomes the single mitochondrion forms an irregular canal running from one end of the body to the other, with a shallow bowl-shaped expansion forming a capsule for the fibrous kinetoplast (mitochondrial DNA). A connexion between the mitochondrial envelope of the kinetoplast and the basal body of the flagellum is not evident, and sometimes the flagellum base is not even apposed to the kinetoplast but lies behind it. Tubular cristae are present in the mitochondrial canal and, by light microscopy, this structure gives a positive reaction for NAD diaphorase suggesting at least some activity in electron transport, even tho at this stage in its life cycle respiration is doubtfully sensitive to cyanide and cytochrome pigments are in all probability absent.
The region of the cytoplasm between the nucleus and the flagellar pocket has all the trappings associated with secretory cells in higher animals, or with the secretion of surface structures in phytoflagellates. just behind the nucleus a limb of granular reticulum subtends a Colgi stack of flattened saccules with attendant vesicles. Close to the distal pole of the Golgi complex is a network of smooth-membraned cisternae, termed here the agranular or secretory reticulum, which undergoes localized swelling with the accumulation of a secretory product to form large spherical sacs or vacuoles. These network-linked vacuoles probably correspond to the post nuclear vacuole complex visible by light microscopy. From its apparent secretory function this complex is regarded here as being possibly an extension or derivative of the Golgi complex, the smooth-membraned tubules lying alongside the 2 structures possibly representing a link between them.
By analogy with phytoflagellates and the secretory cells of higher animals, it is suggested that the secretion is transported for discharge into the flagellar pocket by way of multivesicular bodies and smooth-walled tubules or vesicles. Spiny pits in the wall of the flagellar pocket, and similar-sized vesicles in the nearby cytoplasm, could be stages in either exocytosis of secretion or endocytosis (pinocytosis). It is tentatively suggested that the secretion may be the material from which the surface coat is formed.
Neither a cytostome nor a contractile vacuole has been observed in T. congolense.
TL;DR: It is concluded that during hypertrophy the number of actin and myosin filaments is increased and that a few weeks after denervation the muscle fibres are greatly reduced in size.
Abstract: (1) An electron-microscopic study was made of normal and denervated muscle fibres in the rat diaphragm. (2) Early after denervation muscle fibres become hypertrophic. The cross-sectional area of the fibres and the number of myofibrils within them are increased. Since filament spacing is not significantly altered, it is concluded that during hypertrophy the number of actin and myosin filaments is increased. (3) A few weeks after denervation the muscle fibres are greatly reduced in size. This atrophy is mainly a consequence of two processes: fragmentation of the muscle fibre, with subsequent degeneration of the fragments; and disintegration of myofilaments.
TL;DR: Significant levels of all five enzymes were detected in most of species investigated and the implication of these findings for the concept of ureotelism is discussed.
TL;DR: The severed axons show a characteristic mode of degeneration and at three months some appear to be phagocytosed by oligodendroglia which also contain lamellated inclusion bodies.
Abstract: The synaptic organization of the plexiform layer of the prepyriform cortex in the rat has been studied with the electron microscope both in the normal and after ipsilateral olfactory bulb removal. Survival times ranged from six hours to three months. In normal preparations synaptic contacts occur mainly on dendritic branches, spines or lateral projections. Gray's Type I contacts are most frequent and Type II contacts usually contain flattened vesicles after formalin fixation. Degeneration of the presynaptic bags begins within 24 hours after the lesion and some degenerated bags are still seen after three months survival. During this time degenerated bags are apparently removed by astroglia but the spine tips appear to be unaffected by the phagocytosis. Glia or other processes may come to occupy the denervated sites. The evidence for possible reestablishment of new contacts is considered. The severed axons show a characteristic mode of degeneration and at three months some appear to be phagocytosed by oligodendroglia which also contain lamellated inclusion bodies.
TL;DR: The authors presented a revised version of a paper presented to the Conference of Teachers in Approved Schools on "Language, life and learning", organised by the Home Office Children's Departmer t Development Group and the Programme in Linguistics and English Teaching (University College London) at Sunningdale, 1969.
Abstract: ∗ This is a revised version of a paper presented to the Conference of Teachers in Approved Schools on “Language, life and learning”, organised by the Home Office Children's Departmer t Development Group and the Programme in Linguistics and English Teaching (University College London) at Sunningdale, May 1969. I am much indebted to Professor Basil Bernstein for his very helpful comments on the paper, which already owes a lot to the inspiration of his work.
TL;DR: The properties of β‐galactosidase attached to cellulose and DEAE‐cellulose sheets arc described and the results of long‐term stability tests are given.
Abstract: The properties of β-galactosidase attached to cellulose and DEAE-cellulose sheets arc described. Those insoluble enzyme derivatives obey the Michael-Menten relationship but, the measured kinetic parameters are very dependent on the flow conditions. The results of long-term stability tests are given.
TL;DR: In this paper, a theoretical study of the free periods of oscillation of an incompressible inviscid fluid, bounded by two rigid concentric spheres of radii a, b (a > b), and rotating with angular velocity Ω about a common diameter, is made.
Abstract: A theoretical study is made of the free periods of oscillation of an incompressible inviscid fluid, bounded by two rigid concentric spheres of radii a, b (a > b), and rotating with angular velocity Ω about a common diameter. An attempt is made to use the Longuet-Higgins solution of the Laplace tidal equation as the first term of an expansion in powers of the parameter e = (a − b)/(a + b), of the solution to the full equations governing oscillations in a spherical shell. This leads to a singularity in the second-order terms at the two critical circles where the characteristic cones of the governing equation touch the shell boundaries.A boundary-layer type of argument is used to examine the apparent non-uniformity in the neighbourhood of these critical circles, and it is found that, in order to remove the singularity in the pressure, an integrable singularity in the velocity components must be introduced on the characteristic cone which touches the inner spherical boundary. Further integrable singularities are introduced by repeated reflexion at the shell boundaries, and so, even outside the critical region the velocity terms contain what may reasonably be described as a pathological term, generally of order e½ compared to that found by Longuet-Higgins, periodic with wavelength O(ea) in the radial and latitudinal directions.Some consequences of this result are discussed.
TL;DR: Optimum conditions for the enzyme assay suggest that the dimer contains the essential requirements for the catalytic function of the protein, and the implications of these findings are discussed.
Abstract: Glucose-6-phosphate dehydrogenase from human erythrocytes shows successive aggregation-dissociation equilibria. The effects of salt concentration and pH show that a molecule of 210,000 molecular weight and s20,w of 9.0 S dissociated to a half-molecule of 105,000 molecular weight and s20,w of 5.6 S. Evidence for this being a discrete dissociation was provided by molecular weight determinations, relation between sedimentation coefficients and molecular weights, and the occurrence of skew patterns at a particular degree of dissociation.
Some aggregation of the molecule to give apparent molecular weights above 210,000 occurred at low salt concentrations in the pH range 6–7.
Reaction with maleic anhydride gave a species of molecular weight 53,000 and s20,w 3.4 S, indicating that in the native protein the predominant molecular species (210,000) was a tetramer.
The nature of the dissociations indicate the dissimilarities between the subunit contacts in the tetrameric molecule. Optimum conditions for the enzyme assay suggest that the dimer contains the essential requirements for the catalytic function of the protein, and the implications of these findings are discussed.