Emerging Policy Issues and Research Priorities on Western Hemisphere Integration

International Relations/Trade,

GLOBAL CHALLENGES: LOCAL ISSUES

International Development,

HOW POLICY DECISIONS ARE MADE IN CANADIAN AGRICULTURE

Agricultural and Food Policy,

Subacute injective endocarditis: A bacteriological, serological and histological study

1.) Organisms can be isolated from the blood of many cases of subacute infective endocarditis but not from all. 2.) The organism most commonly isolated is a streptococcus of non-haemolytic type. 3.) Cultures made from the blood during the last few days of life may reveal organisms which have entered the blood stream as part of a terminal invasion. 4.) Pneumococci and other pyogenic organisms isolated from these cases are most frequently terminal invaders. 5.) Cultures made after death from the blood are unreliable as a means of studying diseases due to streptococci unless the observations are adequately controlled, as these organisms occur very commonly as terminal or agonal invaders of the blood stream. 6.) Failure to isolate streptococci from the blood in cases of this disease has not been due to defective technique. 7.) The technique of blood culture has been studied experimentally. Trypsinized media appear to be the best but satisfactory results can be obtained with media containing sodium citrate in a concentration of 0.2 per cent. 8.) The course of the septicaemia in this disease has been studied quantitatively. The number of organisms is usually small and the increase in numbers is slow and irregular. 9.) The serum of the patient contains agglutinins for the organism producing the disease. 10.) The blood of a patient with infective endocarditis can sterilize itself in vitro. 11.) The bacteria isolated from cases of this disease do not form a homogeneous group. 12.) There is evidence that the bacteria isolated are not in the same condition as those in a laboratory culture, but that they are less capable of active growth. 13.) Delay in growth in blood cultures is chiefly dependent upon the peculiarities of the organism present in the blood. 14.) Experimental production of endocarditis in rabbits is irregular and uncertain. 15.) Details of the progress of the septicaemia and production of antibodies in the experimental animal resemble closely those in the human disease. 16.) No evidence has been obtained of the existence of any property of elective localization in the organisms isolated from the human or the experimental disease. 17.) Experiments are recorded on the production of endocarditis by the inoculation of pneumococci into immunized rabbits. 18.) In most of the cases of infective endocarditis with a negative blood culture bacteria can be demonstrated in the vegetation but they appear to be in a degenerate condition. 19.) Attention is drawn to the resemblance between the lesions in the valves in this disease and that in the submiliary nodule in rheumatic fever. 20.) Submiliary nodules have not been found in the heart muscle of cases of subacute infective endocarditis. 21.) Attempts at specific therapy by means of a specially prepared serum and by means of transfusion of blood from an immunized donor have not produced any beneficial effect in the cases in which they have been tried. 22.) The significance of these findings in relation to certain features of the disease is discussed

A remote sensing method for resolving depth and subpixel composition of aquatic benthos

The problem of subpixel heterogeneity in cover types has been addressed in terrestrial environments by the application of linear spectral unmixing techniques. However, in aquatic systems the interceding depth of water causes the apparent reflectance of the substrate to diverge from a linear model, and if depth is unknown these methods cannot be applied. A new technique is presented in which the conventional spectral unmixing method has been modified to calculate depth at each pixel in addition to the proportions of substrate type. The technique requires knowledge of the reflectance spectra of m pure substrata in n (n > m) spectral bands at depth 0 and the water diffuse attenuation coefficients for the site in the same bands. Depth, z, can be entirely unknown. The method is comparable to "classical" spectral unmixing and proceeds by performing a Gaussian elimination for endmember quantities and then solving the remaining nonlinear function of z for f(z) = 0 by successive approximation. Computer-based models are used to test the technique with realistic water diffuse attenuation coefficients and random spectra and actual spectra of coral reef substrata. The robustness of the technique is assessed against three forms of introduced error: measurement errors on the spectra to be unmixed, differences between the true endmember spectra and those used in the analysis, and measurement error on the water diffuse attenuation coefficients. The results of these tests imply the technique is sufficiently robust for use on real data. Furthermore, spectral unmixing of aquatic systems appears to be relatively insensitive to inaccuracies in depth estimation and offers great utility for benthic mapping

Differential effects of depleting agents on cytoplasmic and nuclear non-protein sulphydryls: a fluorescence image cytometry study.

The intracellular distribution of glutathione (GSH) was measured by a quantitative image cytometry method, using the sulphydryl-reactive agent mercury orange. This readily forms fluorescent adducts with GSH and other non-protein sulphydryls (NPSH), but reacts much more slowly with protein sulphydryls. Under optimum staining conditions mean integrated mercury orange fluorescence per cell was closely correlated with a standard biochemical assay for GSH. Use of the DNA dye DAPI as a counterstain allowed measurement of nuclear NPSH. The mean nuclear-cytoplasmic ratio was 0.57 +/- 0.05. Isolation of nuclei under aqueous conditions resulted in the loss of approximately 90% of mercury orange fluorescence, compared with nuclear fluorescence from intact cells, suggesting that background labelling of protein sulphydryls or other macromolecules is low. Depletion of GSH with N-ethylmaleimide or diethylmaleate decreased mercury orange fluorescence in the nucleus and cytoplasm to a similar extent. In contrast, mercury orange fluorescence in the nucleus was much more resistant to DL-buthionine-S,R-sulphoximine (BSO) depletion than that in the cytoplasm. This finding is compatible with a distinct pool of GSH in the nucleus that is comparatively resistant to BSO depletion. Alternatively, the retention of fluorescence in the nucleus following GSH depletion by BSO treatment might be due to accumulation of cysteine. These findings have implications for cancer treatment since the level of NPSH in the nucleus might be a more important determinant of resistance to DNA-damaging agents than that in cytoplasm. The image cytometry method described here is quantitative, allows a measure of tumour cell heterogeneity and can be applied to small biopsy samples obtained by fine-needle aspiration. Thus it appears suitable for prospective clinical studies in cancer patients, and for monitoring the effects of GSH-depleting agents used as adjuncts to cancer chemotherapy or radiotherapy

Short-term effects of deep ploughing on soil C stocks following renewal of a dairy pasture in New Zealand

In New Zealand’s high producing permanent pastures the topsoil constitutes a large reservoir of soil organic carbon (SOC), which shows a marked stratification with depth. As consequence, sub-surface layers can contain 10 times less carbon than the surface soil. In permanent pastures with high carbon inputs, the formation and decomposition of these surface SOC stocks are often at equilibrium and C storage shows little change over time. Pastoral based dairy systems utilising ryegrass plus clover cultivars require renewal every 7-10 years to avoid reversion to less productive grasses. This may involve spring cultivation (either no-till, shallow till or full cultivation), summer forage cropping and autumn re-grassing. It has been hypothesised that SOC stocks can be increased by inverting the soil profile at pasture renewal through infrequent (once in 25-30 years) deep mouldboard ploughing (up to 30 cm depth). Increased C sequestration occurs when the new grass quickly rebuilds SOC stocks in the new topsoil (exposed low C sub-soil) at a rate faster than the decomposition of SOC in the rich former topsoil transferred to depth (now below 15 cm). However, benefits form accelerated C storage may be offset if crop and pasture production is adversely affected by the ploughing event (e.g., as result of compaction or excessive drainage). Hence, the aim of this work was to assess the short-term effects of infrequent inversion tillage of long-term New Zealand pastoral-based dairy soils under summer crop management and autumn re-grassing. An imperfectly drained Typic Fragiaqualf under dairy grazing was deep ploughed (approx. 25 cm) and re-sown with turnip in October 2016; other treatments included were shallow (< 10 cm) cultivation and no-till. The site was core sampled (0-40 cm) before cultivation and after 5 months of turnip growth to assess changes in SOC. Plant growth, herbage quality, and nutrient leaching were monitored during the 5-month period; root growth was assessed at the end of the crop rotation. Full cultivation transferred SOC below 10 cm depth, as expected. Soil bulk density decreased whereas root mass increased (10-20 cm depth; P < 0.05) under deep cultivation only. Besides, losses of mineral N were attenuated under deep tillage, resulting in a relative increase in crop yield. The potential for infrequent inversion tillage increasing soil C sequestration as a greenhouse gas (GHG) mitigation tool is currently being tested at other sites in New Zealand

Structural complexity governs seagrass acclimatization to depth with relevant consequences for meadow production, macrophyte diversity and habitat carbon storage capacity

Analyses of the integrated seagrass response to depth support the previously documented low plasticity and consistent shade-adapted leaf physiology of a habitat-builder that dominates well-illuminated reef environments. Two structural responses, "canopy-opening" and "below-ground-mass-depletion", govern the photoacclimatory response and facilitate, respectively, light penetration within the canopy and functional adjustments in whole-plant carbon balances. Conversely, "canopy-closing" may also explain dense canopies formed close to the waterline, as they provide shade and photoprotection to a susceptible leaf physiology under high-light. Canopy light attenuation is primarily regulated by the leaf area index (LAI), which is governed by changes in shoot size and density. Shoot density diminishes non-linearly with depth, while shoot size increases to a maximum followed by a decline. The initial increase in shoot size, which resembles a self-thinning response, increases LAI and meadow production in shallow depths. These seagrass structural adjustments have relevant ecological implications. Canopy-thinning allows macrophyte diversity to increase with depth, while seagrass production and carbon storage diminish exponentially, and are maximal only in a shallow coastal fringe. The results support the universality of plant self-thinning, from phytoplankton to complex canopies, likely the consequence of simple physical laws related to light limitation and pigment self-shading within photosynthetic structures and communities