Showing papers by "University of St Andrews published in 1968"
TL;DR: The standard appearances of negatively and positively stained fibrils are shown and the correlation between the two staining patterns in that figure is based on the findings of Nemetschek5.
Abstract: THE length of the tropocollagen (TC) molecule is about 44 times that of the native collagen period (D) (refs 1–4) The standard appearances of negatively and positively stained fibrils are shown in Fig 1 and the correlation between the two staining patterns in that figure is based on the findings of Nemetschek5
309 citations
TL;DR: In this paper, a new interatomic potential for helium is proposed of the form: with a=0·675 a, α=4·390 a -1, β=3·746 × 10-4 a -6 and A=398·7 ev.
Abstract: A new interatomic potential for helium is proposed of the form: with a=0·675 a, α=4·390 a -1, β=3·746 × 10-4 a -6 and A=398·7 ev. The long-range attraction has the correct theoretical dependence on the separation with the terms having the coefficients as calculated by Dalgarno and Kingston and by Davison. The short-range repulsive part of the potential was fitted to the calculated potential energy values of Phillipson and the experimentally determined values of Amdur and his co-workers. In addition the parameters were adjusted so that the potential reproduces the experimentally determined second virial coefficient for helium.
268 citations
175 citations
TL;DR: There is compelling evidence in amphibia and in the insect Tipula that this DNA is derived from the chromosomal nucleolar organizer region which contains the ribosomal cistrons, and this conclusion is supported by the recent finding that in ovarian tissue of Xenopus there is a disproportionately greater synthesis of ribosomes.
Abstract: DURING the development of the amphibian oocyte, the germinal vesicle becomes enlarged and can be seen to contain very many nucleoli1,2 instead of the four which would be expected from the tetraploidy of the egg nucleus. The RNA of these nucleoli is similar in base composition to ribosomal RNA3 and each nucleolus contains a small amount of DNA4–6. Amphibian oocyte nucleoli can be hypotonically disrupted to reveal DNP rings in the shape of beaded circles or necklaces2,6. There is compelling evidence in amphibia2,6,7 as well as in the insect Tipula8 that this DNA is derived from the chromosomal nucleolar organizer region which contains the ribosomal cistrons9,10. This conclusion is supported by the recent finding that in ovarian tissue of Xenopus there is a disproportionately greater synthesis of ribosomal cistrons11 which leads eventually to a higher proportion of them than that found in DNA of somatic tissues11,12. In Bufo, the nucleolar DNA migrates as granules from the chromosomal bouquet to the periphery of the nucleus where, at later stages, the granules give rise to nucleoli5. A similar process occurs in Xenopus where Feulgen-positive material appears in the oocyte nucleus as a “nuclear cap” at leptotene13. After zygotene this cap disperses and numerous nucleoli are formed which contain one or several DNA cores or rings14.
133 citations
TL;DR: The measuring device enables slow movements of small objects, such as arthropod eyes, to be detected without placing a significant load on the moving system.
100 citations
TL;DR: In this article, the authors discuss the use of an inert liquid as a seal in preventing the loss of volatile components from dissociable compounds or their melts, with particular reference to the growth of compounds having dissociation pressures in excess of one atmosphere.
87 citations
TL;DR: The ovaries of newly metamorphosed Xenopus females contain oocytes in all stages of early meiotic prophase and it is proposed that primary replicas of the chromosomal nucleolar organizer undergo a series of post-detachment replications.
Abstract: SUMMARY The ovaries of newly metamorphosed Xenopus females contain oocytes in all stages of early meiotic prophase. In pachytene nuclei extrachromosomal nucleolar DNA appears in the form of a thin cap covering one side of the nucleus. During pachytene this cap of DNA enlarges to occupy half the nucleus. After pachytene the nucleus grows rapidly and the cap of DNA disperses into numerous tiny granules which become scattered throughout the nucleoplasm. Autoradiographs of cells which have been incubated with PHJthymidine, and microspectrophotometric measurements of the Feulgen dye contents of nuclei in various stages of meiosis, show that the extrachromosomal nucleolar DNA is synthesized during the pachytene and immediate post-pachytene stages. Microspectrophotometric comparison of the Feulgen dye contents of post-pachytene nuclei in which the DNA cap has dispersed, and similarly prepared mouse liver nuclei, show that the post-pachytene nuclei have about 30 fifig of extrachromosomal pachytene nucleolar DNA. In PHJthymidine autoradiographs early pachytene nuclei are less heavily labelled than late pachytene and early diplotene nuclei. Consequently it is proposed that primary replicas of the chromosomal nucleolar organizer undergo a series of post-detachment replications.
86 citations
TL;DR: The trisodium salt of nitrilotriacetic acid (NTA) seems to be a promising “anti-pollutant”, to prevent fish-kills in case of short-term breakdown of normal pollution controls.
Abstract: COPPER and zinc are surprisingly widespread pollutants of water. In wilderness areas they may endanger fish in otherwise clean rivers as the result of mining operations1. In British industrial areas, they commonly contribute an average of 23 per cent of total toxicity of mixed pollution for fish, and in some rivers a much higher proportion2. Furthermore, trace concentrations, one-tenth to one-twentieth of accepted standards for drinking water, can be lethal for fish in regions where surface water is very soft1. In such circumstances, year-round prevention of “spills” of metal pollution can be difficult. The trisodium salt of nitrilotriacetic acid (NTA) seems to be a promising “anti-pollutant”, to prevent fish-kills in case of short-term breakdown of normal pollution controls.
82 citations
TL;DR: Staining with fast green before and after treatment with Van Slyke reagent indicates a change from lysine- rich to arginine-rich histone in the maturing spermatid.
Abstract: The testis of Nucella consists of numerous tubules, all directed inwards and joining to form a common testicular duct. In a single tubule the spermatogonia lie round the periphery. Mature sperm line the lumen of the tubule. Cells in the same stage of spermatogenesis are grouped together and all members of a group pass through spermatogenesis in phase. Staining with fast green before and after treatment with Van Slyke reagent indicates a change from lysine-rich to arginine-rich histone in the maturing spermatid. Sperm of Nucella are motile throughout their length. The sperm are thread-like and about 80 µ long. The head is Feulgen-positive and about 40 µ long. The mid-piece lies behind the head and is about 8 µ long. The flagellum runs from the front end of the head to the tip of the tail; in the head it is completely surrounded by the nucleus. The spermatogonia contain two centrioles situated near the nucleus and a conspicuous Golgi complex. There are synaptinemal complexes in spermatocyte nuclei in the synapsis stage. In the early spermatid the centriole pushes a tube through the nucleus. This tube is lined by nuclear membrane and is occupied by the anterior portion of the flagellar shaft. The nucleus elongates and the nucleoprotein condenses into strands arranged helically along the long axis of the nucleus. These strands fuse to form lamellae, which disappear in the mature sperm. Mitochondria aggregate at the base of the early spermatid nucleus and form a loose spiral around the flagellar shaft. The outer mitochondrial membranes fuse. The mid-piece of the mature sperm consists of a large tubular mitochondrion enclosing a portion of the flagellar shaft. At the early spermatid stage a pro-acrosomal granule is formed from a large Golgi complex. From this the acrosome develops; it consists of a cone and an acrosome granule. There are two sets of microtubules associated with the acrosome, one lying within the cone, the other outside the cone and separated from it by a ‘ragged membrane’. The microtubules of the outer set extend backwards along the head for two-thirds of its length. The centriole which gives rise to the flagellar shaft lies at the anterior end of the head and is separated from the acrosome by a thin layer of nucleoprotein and a double layer of nuclear envelope. There is no second centriole or derivative thereof in the mature sperm. In the tail groups of coiled fibres are associated with each pair of the peripheral flagellar fibrils.
80 citations
TL;DR: Evidence is presented that the chemoreceptors of the Decapod (Crustacea) walking leg are located in rows of branched hairs and experiments indicate that the funnel canal organ is a dually innervated mechanoreceptor which responds to strain applied to the cuticle.
78 citations
TL;DR: Rainbow trout (Salmo gairdnerii Richardson) showed strong avoidance reactions to sub-lethal concentrations of zinc sulphate as mentioned in this paper, with threshold avoidance level 5.6 μg/l of zinc added to laboratory water.
TL;DR: In this article, the thermal degradation of thermally and anionically prepared polystyrenes was studied at temperatures where volatile formation is negligible, and it was shown that these weak links are distributed predominantly at random within the polymer chains, although the possibility that a small proportion are sited at chain ends cannot be entirely excluded.
TL;DR: In this paper, the effect of sinusoidal temperature fluctuations in the melt on the growth of a crystal is investigated by solving the concentrationdiffusion and heat-conduction equations for both solid and liquid phases in a linear approximation.
TL;DR: Label distribution at first metaphase in spermatocytes stemming from sperMatogonia which incorporated [ 3 H]thymidine during the penultimate intermitotic S shows that random segregation and assortment of labelled and unlabelled chromatids took place at the ultimate sper matogonial mitosis.
Abstract: In male Triturus vulgaris at 16 °C the pre-meiotic synthesis of DNA ( S -phase) takes 9-10 days. The S -phase starts 1-2 days after completion of the ultimate spermatogonial mitosis, and extends into leptotene. Heterochromatic regions, most of which lie close to the centromeres, start and finish replicating about 1 day later than other parts of the chromosomes. Synapsis starts 6 days after the end of pre-meiotic S and is completed 8 days later. Pachytene lasts for 4 or 5 days, diplotene for 1 or 2 days, and first metaphase occurs 20 or 21 days after the end of pre-meiotic S . Label distribution at first metaphase in spermatocytes stemming from spermatogonia which incorporated [ 3 H]thymidine during the penultimate intermitotic S shows that random segregation and assortment of labelled and unlabelled chromatids took place at the ultimate spermatogonial mitosis.
TL;DR: From 1960 to 1966, the activity of Oldoinyo Lengai took the form of quiet extrusion of carbonatite lava, but the style of activity changed abruptly and violent ash eruptions took place.
Abstract: From 1960 to August, 1966, the activity of Oldoinyo Lengai took the form of quiet extrusion of carbonatite lava. In August, 1966, the style of activity changed abruptly and violent ash eruptions took place. The activity varied from minor emissions of ash to major Plinian and Vulcanian type eruptions. A new ash-cone built up within the crater and ash was widely distributed on the slopes of the volcano and over the surrounding countryside. The ash consists of sodium carbonate mixed with crystals of nepheline, pyroxene, wollastonite, apatite, melanite and pyrite. Also blocks of ijolite and melteigite were ejected during the activity.
TL;DR: In this paper, a linear sweep voltammetric study of thin layer semiconducting tin oxide layers on glass substrates revealed three regions of electrochemical interest: the anodic region, oxygen or chlorine evolution occurs without disruption of the surface.
Abstract: Linear sweep voltammetric studies of thin layer semiconducting tin oxide layers on glass substrates revealed three regions of electrochemical interest. In the anodic region, oxygen or chlorine evolution occurs without disruption of the surface. In the intermediate region of potentials, cathodic‐anodic processes attributable to charging and discharging of positive surface states occur. The charging‐discharging process is most pronounced in the presence of high concentrations of hydrogen ions and chloride ions and is closely related to the specific adsorption of chloride ion. In the cathodic region, hydrogen ion discharge is accompanied by a disruption of the tin oxide layer, which is reduced to metallic tin.
TL;DR: In this paper, a more general comparison equation theory for difference equations is developed, exploiting the fact that a difference equation can be considered as a differential equation of infinite order, and applying the theory to first order difference equations a useful generalization of the Euler-Maclaurin summation formula is found.
Abstract: In a previous paper [1] it was shown how to develop solutions to difference equations analogous to WKB solutions to differential equations. In the work now reported a much more general “comparison equation” theory [2] is developed for difference equations, exploiting the fact that a difference equation can be considered as a differential equation of infinite order. Second order difference equations are considered in the main; by applying the theory to first order difference equations a useful generalization of the Euler-Maclaurin summation formula is found.
TL;DR: In this article, a triad of gravity waves in a uniform shear flow is considered, and a remarkably powerful second-order resonant interaction may take place, characterized by large growth rates of waves which propagate in directions oblique to that of the primary flow.
Abstract: Among a triad of gravity waves in a uniform shear flow, a remarkably powerful second-order resonant interaction may take place. This interaction is characterized by large growth rates of waves which propagate in directions oblique to that of the primary flow, and by a systematic transfer of energy from the primary flow to such waves. Most of the energy transfer takes place in the vicinity of a ‘critical layer’, where viscous forces are dominant. Provided the resonance condition may be satisfied, a uniform shear flow which is perturbed by a two-dimensional wave of small but finite amplitude may be unstable, owing to the growth of two initially infinitesimal oblique waves which complete the resonant triad.
TL;DR: In optokinetic nystagmus the exact form of the impulse sequences are described for each muscle, which are the consequence of a visually driven central programme which takes no account of the movement which it generates.
Abstract: 1. The actions of the nine eyecup muscles of the crab during horizontal optokinetic movements are described. 2. Each muscle includes a wide spectrum of fibre types, ranging from phasic, with sarcomere lengths of 3-4 µ m., through intermediate, to tonic fibres with sarcomeres of 10-12 µ m. Each muscle receives at least one slow and one fast motoneuron, but no inhibitory supply. The slow axons predominantly innervate the tonic muscle fibres while the fast axons innervate the phasic ones. 3. Slow movement and the position of the eyecup in space are controlled by the frequency of slow motoneuron discharges. All muscles collaborate at every position. The phasic system is recruited during rapid eyecup movements of large amplitude. 4. In optokinetic nystagmus the exact form of the impulse sequences are described for each muscle. They are the consequence of a visually driven central programme which takes no account of the movement which it generates. Movements in opposite directions involve different central programmes; the one is not merely the reverse of the other. There is no effective proprioceptive feedback from the eyecup joint or from muscle tension receptors.
TL;DR: In this article, the cis octadecenoic esters have been converted to cyclopropane compounds by reaction with zinc-copper couple and di-iodomethane.
TL;DR: In this paper, the authors compared the experimental results of Mollard and Flemings [Trans. AIME 239 (1967) 1526, 1534] on the breakdown of the Pb-Sn system.
TL;DR: In this paper, an alternative constitutive relation, which takes account of the entire strain-history of the motion, leads to the more reasonable result that the equilibrium is stable whenever the fluid has a "fading memory".
Abstract: A recent analysis by Gupta (1967) suggests that a layer of elastico-viscous fluid at rest between parallel plane boundaries may be in unstable equilibrium. This surprising result is attributable to the inadequacy of the constitutive equation adopted by Gupta as the basis for his analysis. An alternative constitutive relation, which takes account of the entire strain-history of the motion, leads to the more reasonable result that the equilibrium is stable whenever the fluid has a ‘fading memory’.
TL;DR: The component acids of seed oils from over fifty legumes and over fifty other species are reported, and their potential value is discussed.
Abstract: The component acids of seed oils from over fifty legumes and over fifty other species are reported, and their potential value is discussed.
TL;DR: The following account points to the conclusion that the superposition theory is applicable only to a cleaned cornea because the actual anatomy suggests quite a different optical system.
Abstract: THE compound eye of the firefly is the one outstanding example which shows evidence of an image which is formed by the combination of rays that have entered by several facets. The original account by Exner1 includes a description and photograph of the erect image that can be found behind the cleaned cornea of the firefly Lampyris. This image has been confirmed by others2 and a theoretical explanation of it supposes that an inverted first image is formed within each corneal cone by the curvature of its front surface and that an erect second image is then formed by the curved surface of the proximal tip of the corneal cone3. The erect superposition image, however (which undoubtedly exists if the cornea is well cleaned), does not lie in the place of the receptors4 and there is no evidence that it has a functional significance. In fact, the superposition theory depends on the unlikely existence of an optically homogeneous and transparent region between the cornea and the layer of receptors. Despite its importance to the theory, the anatomy of the firefly retina remains unknown. The following account, based on Photuris versicolor, points to the conclusion that the superposition theory is applicable only to a cleaned cornea because the actual anatomy suggests quite a different optical system.
TL;DR: During imposed tilt the eyecup or the crab tends to preserve an absolute position which depends upon the tonic activity of eight of the nine eyec up muscles, but in neither case is there a correlation between individual impulses to the muscles of the right and left eyecups which are active at the same time.
Abstract: 1. During imposed tilt the eyecup or the crab tends to preserve an absolute position which depends upon the tonic activity of eight of the nine eyecup muscles. The detailed activity of all these muscles during imposed tilt in different planes has been recorded intracellularly. 2. The slow- and fast-motoneurone discharges to the eyecup muscles differ in that the former have intervals which are more variable at lower frequencies but the latter are more variable at higher frequencies. 3. The standard deviation of the interval between impulses is 20-30% of the mean interval for a wide range of frequencies of the tonic motoneurones. This large scatter is tolerable because the slow muscle fibres are sluggish and because the eyecup is also visually stabilized by a system of long time-constant. 4. In roll the two eyecups move in opposite directions relative to the midline of the animal. In pitch the two eyecups move in the same direction relative to the body of the animal, but in neither case is there a correlation between individual impulses to the muscles of the right and left eyecups which are active at the same time. 5. Possible mechanisms of linkage between the two eyecups are discussed.