The Royal Society
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* Dữ liệu chỉ mang tính chất tham khảo
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Unstalked crinoids of the antarctic continental shelf, notes on their natural history and distribution An account is given of the natural history, distribution and relative abundance of the comatulids of the Antarctic continental shelf. On the whole they form a distinctive geographical assemblage, that, cut off from northern influence, has evidently evolved in isolation since at least from the beginning of the Pleistocene or Quaternary Period. Where large enough numbers have been encountered the distribution of six of the seventeen known shelf species has been shown to be circumpolar, and at least one of the six, the largest and most mobile, appears to have spread, or perhaps even now is spreading, northwards to lower latitudes via the submarine ridges that radiate outwards from Antarctica.
The Royal Society - Tập 246 Số 734 - Trang 327-379 - 1963
A memory system in the monkey A neural model is presented, based largely on evidence from studies in monkeys, postulating that coded representations of stimuli are stored in the higher-order sensory (i.e. association) areas of the cortex whenever stimulus activation of these areas also triggers a cortico-limbo-thalamo-cortical circuit. This circuit, which could act as either an imprinting or rehearsal mechanism, may actually consist of two parallel circuits, one involving the amygdala and the dorsomedial nucleus of the thalamus, and the other the hippocampus and the anterior nuclei. The stimulus representation stored in cortex by action of these circuits is seen as mediating three different memory processes: recognition, which occurs when the stored representation is reactivated via the original sensory pathway; recall, when it is reactivated via any other pathway; and association, when it activates other stored representations (sensory, affective, spatial, motor) via the outputs of the higher-order sensory areas to the relevant structures.
The Royal Society - Tập 298 Số 1089 - Trang 85-95 - 1982
Ultrastructural features of the sensori-motor cortex of the primate cooled to 2°K or lower. Rollin (1936) found that the thermal insulation of vessels containing liquid helium was much worse below than above the A point. He explained his observation by assuming the existence of a thin layer of liquid helium on the inside wall of the connecting tube, and thought it probable that the change in thermal conductivity of this film at the A point gave rise to the anomalous effects observed. As the result of more recent (unpublished) experiments Rollin and Simon* have put forward the other explanation that the film creeps up the tube and evaporates eventually. It is obvious that all these phenomena may have a common explanation and it was the object of the experiments described in this paper and the following paper to investigate the behaviour of He 11 in contact with solid surfaces systematically. The phenomena had to be investigated from various aspects and this made experiments necessary which varied in purpose and character to some extent. For simplicity’s sake we will therefore give, together with the description of each experiment, a short discussion and summarize at the end of the second paper all results in a general discussion on the whole phenomenon. All experiments were carried out in the same cryostat; and for different experiments only the experimental chamber and the experimental arrangement in it were altered.
The Royal Society - Tập 285 Số 1006 - Trang 123-139 - 1979
Agricultural Development and Advisory Service (A. D. A. S. ) recommendations to farmers on manure disposal and recycling Farm animal excreta may fall directly on grazed crops or be collected from housed animals as semi-liquid slurry or more solid manure. Estimates are given of the total amounts of N in animal excreta in the U. K. and in the various forms in which it may be collected from housed animals. The factors affecting the losses of N from stored manures and the availability to crops of the N content of manures are reviewed. The optimum use of the N content of manures as a crop nutrient is discussed in relation to practical farming problems including the costs to farmers of storing manures and slurries, the difficulties of applying these materials to land at particular times of the year, and the risks of causing pollution of water.
The Royal Society - Tập 296 Số 1082 - Trang 329-332 - 1982
Nitrogen cycling in United Kingdom forests: the relevance of basic ecological research
Following recent reviews on nutrient cycling in temperate and British forests, two aspects of N cycling are selected for examination because of their fundamental importance and their relevance to management—ecosystem research and mobilization of N during decomposition. Despite the early work by J. D. Ovington and P. J. Rennie, only two major forest ecosystem studies have been developed in Britain. Summaries from these ecosystems show that they span the range of temperate forests in the N cycling characteristics. The
Pinus nigra
plantation on Culbin Sands is functioning on a low capital with low rates of transfer and shows N deficiency after 40 years. In contrast, the mixed deciduous Meathop Wood has a much larger capital of N and higher rates of transfer. The
Pinus
ecosystem retained a high proportion of added fertilizer N in the biomass and forest floor, and increased growth rates can be explained through N recycling within the trees. Basic concepts of N mineralization are reviewed and it is shown that they need to be modified for application to forests. Uptake by saprophytic and mycorrhizal fungi from the pool of soluble organic N can short-circuit the ammonification pathway and N can be released from substrates with a high C:N ratio by lysis of microbial tissues and faunal feeding. Some examples of evidence of these processes are given, stressing the spatial and temporal mosaic of substrates acting as sinks and sources of N. Management practices can have a marked effect, not only on the quantity of N returned in residues, but on its availability as a result of variation in the associated carbon. However, growth experiments have shown that substrates with C:N ratios above 35 can release significant amounts of N to tree seedlings. A final examination of the recycling processes in the four nutritional stages of a forest emphasizes the importance of the effects of management on the short- and long-term balance of mobilization processes in the forest soil.
The Royal Society - Tập 296 Số 1082 - Trang 427-444 - 1982
An anomaly in the response of the eye to light of short wavelengths
Adaptation of the human eye to long-wavelength light leaves it insensitive to short-wavelengths: a blue flash that is visible in the presence of a yellow adapting field may remain invisible for several seconds after the field has been turned off (see experiment 1 and Appendix). This ‘transient tritanopia’ occurs for a large range of adapting intensities, but is abolished if the adapting field is very bright (experiment 2). The loss of sensitivity is primarily confined to the blue-sensitive cone mechanism (experiments 2
a
, 3 and 4 ; and Appendix) and can be produced by small attenuations of the adapting field (experiment 5). It occurs in both foveal and parafoveal vision (experiment 6) but is absent when adapting and test stimuli are presented to opposite eyes (experiment 7). It was found in a protanope (experiment 9
a
) and, in a modified form, in a deuteranope (experiment 9
b
). No differences in sensitivity were found for blue flashes presented in the light and dark phases of a field flickering at a rate above the fusion frequency (Appendix). The sensitivity of the blue-sensitive mechanism of the eye appears to be controlled not only by quanta absorbed by the blue receptors but also by a mechanism with a different spectral sensitivity
The Royal Society - Tập 278 Số 960 - Trang 207-240 - 1977
Anion-dependent cation transport in erythrocytes A selective survey of the literature reveals at least three major anion-dependent cation transport systems, defined as Na+ + Cl- , K+ + Cl- and Na+ + K+ + Cl- respectively. In human red cells, kinetic data on the fraction of K+ and Na+ influx inhibitable by bumetanide are presented to indicate an Na+ :K+ stoichiometry of 1:2. For LK sheep red cells the large Cl- -dependent K+ leak induced by swelling is shown to share many characteristics with that induced by A-ethyl maleimide (NEM) treatment. NEM has complex effects, both inhibiting and then activating Cl “-dependent K+ fluxes dependent on NEM concentration. The alloantibody anti-L can prevent the action of NEM. In human red cells NEM induces a large Cl- -dependent specific K+ flux, which shows saturation kinetics. Its anion preference is Cl- > Br- > SCN- > I- > NO- >3 MeSO- 4 . This transport pathway is not inhibited by oligomycin or SITS, although phloretin and high concentrations of furosemide and bumetanide (over 0.3 mM) do inhibit. Quinine (0.5 mM) is also an inhibitor. It is concluded that at least two distinct Cl- -dependent transport pathways for K+ are inducible in mammalian red cells, although the evidence for their separation is not absolute.
The Royal Society - Tập 299 Số 1097 - Trang 483-495 - 1982
The temporal context of spatial memory Foraging strategies provide an effective and convenient means of investigating some characteristics of animal intelligence. The temporal and spatial distributions of food in the environment are not entirely random, and animals that use information about these patterns can gain an adaptive advantage over animals that do not. For some types of strategies to be effective, the animal must remember the temporal context of a visit to a spatial location and use this memory to make decisions about the current distribution of food in the environment. Experiments with different species (rat, Hawaiian honeycreeper, Marsh tit, Clark’s nutcracker) have used variations of a delayed conditional discrimination to examine the cognitive processes influencing this type of memory. These include: primacy, recency, proactive interference, retroactive interference, decay, consolidation, and chunking. The results of these experiments provide information about the types of memory processes that animals use when searching for food, and illustrate the usefulness of combining psychological and ethological approaches when studying animal intelligence.
The Royal Society - Tập 308 Số 1135 - Trang 79-86 - 1985
The existence during gestation of an immunological buffer zone at the interface between maternal and foetal tissues In mammalian pregnancy the trophoblast normally constitutes an uninterrupted boundary of foetal tissue in immediate contact with maternal tissue, including blood in some species, and is the decisive immunological barrier to rejection of the foetus as an allograft. The ability of the trophoblast to function as a barrier evidently results from its capacity to resist immunological attack by either alloantibody or alloimmune cells and to prevent immunocompetent cells from reaching and damaging the foetus but, as yet, there is no general agreement regarding the means by which it exercises these functions. In view of the dramatic hormonal changes that occur during pregnancy and the undisputed involvement of trophoblast in these endocrine events, the possibility exists of an interaction between the hormones of pregnancy and the immunological phenomena. The present account furnishes evidence that endocrine activity at the maternal surface of the trophoblast, the presumptive site of the immunological frontier between foetus and mother, may be a factor in its local survival at implantation. The placental hormones so far known that are capable of blocking the antigen receptor sites of the mother’s lymphocytes and thus preventing the latter from reacting with the foetal antigens are the glycoprotein, human chorionic gonadotrophin (HCG) and the polypeptide hormone, human chorionic somatomammotrophin (HCS) or human placental lactogen (HPL), both of which are specific to the human placenta. The origin of these hormones, their spatial distribution and their probable interaction with placental steroid hormones are discussed. It is argued that the place of highest concentration of these hormones is on the surface of the syncytial microvilli and the adjacent caviolae of the apical plasma membrane, as well as on the surfaces of the persisting cytotrophoblastic cells of the basal plate (cytotrophoblastic shell), the cell islands and the septa - precisely where the immunological challenge of the foetal allograft to the maternal host occurs. An explanation is offered for the continuing production of the voluminous quantities of these hormones during human pregnancy.
The Royal Society - Tập 271 Số 912 - Trang 343-361 - 1975
Macromolecules in mollusc shells and their functions in biomineralization
Mollusc shells are used as a model for studying ‘organic-matrix -mediated’ biomineralization, in which crystals are nucleated and grow in a pre-formed structural framework composed of proteins and polysaccharides. In particular, the possibility that the organic matrix functions as a template for crystal formation by epitaxial growth, is examined. In general, individual organic matrix sheets are composed of a thin layer of β-chitin sandwiched between layers of proteins adopting the antiparallel β-sheet conformation. The protein polypeptide chains are oriented perpendicular to the chitin fibrils. The matrix surfaces contain acidic proteins and polysaccharides. X -ray and electron diffraction patterns of matrices and mineral crystals from the nacreous layers of a bivalve, a gastropod and the cephalopod,
Nautilus
, show that the chitin fibres and the protein polypeptide chains are aligned with the
a
and
b
aragonite crystallographic axes, respectively. This strongly suggests that the mineral formed epitaxially upon the matrix surface. However, as the degree of orientation of the organic constituents is much less than the mineral constituents, it is postulated that the site of nucleation of the mineral crystals comprises only a small part of the matrix structure and is itself composed of well oriented macromolecules, probably acidic proteins. Two acidic proteins, which may constitute part of the nucleation site for calcite in a bivalve, were identified by comparing all the acidic proteins in the calcite layer with those in the aragonite layer. The two proteins were present in the calcite layer only, and in addition were found to have an aspartic-acid -containing amino acid sequence, not present in any of the other soluble matrix proteins. The concept of a matrix composed of a structural core coated with acidic macromolecules, some of which constitute a nucleation site, may well be applicable to other mineralized tissues.
The Royal Society - Tập 304 Số 1121 - Trang 425-434 - 1984
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