Signal Duration as a Factor in Vigilance Tasks

Short signals in a vigilance test generated an inferior initial performance, as compared with longer signals, and resulted in a steeper decrement in performance. A short (1-minute) and a long (2-hour) vigilance task was undertaken by each subject.     

Effects of drill coulter design and soil moisture status on emergence of wheat seedlings

A field experiment is described where three contrasting direct drilling coulters (seed groove openers) were used for a total of twelve drillings at fortnightyly intervals. Wheat was drilled into an undisturbed silt loam soil in a temperate climate during a spring-summer-autumn period in the southern hemisphere. An experimental chisel coulter promoted significantly larger counts of seedling emergence than a triple disc coulter in two of the drillings, and was also superior to a hoe coulter in one of the drillings. In very dry conditions, where in 3 weeks no seedling emergence occurred with any of the coulters, sub-surface seedlings in the grooves made by the chisel coulter had survived in a further two of the drillings than was the case with the triple disc and hoe coulters.These results confirmed that the biological effect of the coulters was largely a function of the physical geometry of the grooves which determined their ability to retain and utilize the liquid and vapour moisture present in the seed micro-environment.     

Experimental acidification of Little Rock Lake,Wisconsin

The controlled acidification of a two-basin lake is described. The lake was divided by a vinyl curtain in 1984; acidification of one basin began in 1985. Target pH values of 5.5, 5.0 and 4.5 are planned for 2-yr increments. Biotic and chemical responses and internal alkalinity generation are being studied. Baseline studies, initial results at pH 5.5, and predictions of lake responses to acidification are described.     

Simulated acid rain effects on fine roots,ectomycorrhizae, microorganisms,and invertebrates in pine forests of the southern United States

A 2-yr study evaluated the effects of acid precipitation on the forest floor community. Throughfall was collected at weekly intervals, acidified to pH 4.3 and 3.6, and applied to throughfall excluded 1 m² plots in a stand of loblolly pine (Pinus taeda L.) in south Mississippi, and in a longleaf pine (P. palustris Mill.) plantation in east Texas. Control plots received ambient throughfall which ranged from pH 3.7 to 6.2 in Mississippi and pH 3.8 to 6.7 in Texas. Five plots of each treatment at each location were destructively sampled after 1 yr and the 5 remaining plots were sampled after 2 yr. Chemical analyses were conducted for all collections of throughfall and litter leachate, and for the fermentation layer, rhizosphere, and mineral soil. After 2 yr, comparisons of the pH 3.6 plots with the controls indicated significant decreases in the number, length and biomass of lateral roots, and the percent and number of ectomycorrhizae. Decreases in these root characteristics for plots subjected to applications of throughfall acidified to near-ambient pH 4.3 were also significant or bordered on significance. Numbers of herbivorous mites increased significantly with decreasing pH, but the predaceous mites appeared insensitive. Treated plots had fewer numbers of some groups of the larger invertebrates, especially earthworms, but variation was generally too great to show significance. The acid treatments had little effect on numbers of nematodes, saprophytic fungi or endomycorrhizal fungi.     

A retrospective study of 11 cases of lungworm (Didelphostrongylus hayesi) infection in opossums (Didelphis virginiana).

A juvenile, female North American opossum (Didelphis virginiana) died of verminous pneumonia caused by Didelphostrongylus haysei despite aggressive treatment with oral fenbendazole, corticosteroids, and antibiotics. This prompted a retrospective study of lungworm infection in opossums, during which 19 additional necropsy reports from opossums were reviewed. Including the subject of this report, a total of 11 (55%) of these cases included a diagnosis of lungworm infection. This diagnosis was considered to have contributed to death in eight out of the 11 cases (73%). Histologically, 10 of the 11 (91%) opossums had granulomatous bronchopneumonia with small to moderate numbers of adult nematodes in the airways and parenchyma. Four of the 11 (36%) opossums had free larvae within the parenchyma or terminal airways. Inflammation was usually associated with larvae, degenerating parasites, and nonintact adult nematodes. Superimposed bacterial pneumonia was evident in three animals, and sections of lung examined from all the opossums were characterized by moderate to severe smooth-muscle hyperplasia in airways, including terminal respiratory bronchioles and alveolar ducts. Nine animals had prominent medial smooth-muscle hyperplasia in small- and medium-sized arterioles. Lesions in other organs, particularly in liver, heart, and gastrointestinal tract, were frequently identified. Three animals had concomitant septicemia or bacterial bronchopneumonia (or both), which contributed to the cause of death. Seven animals had gastric nematodosis (Physaloptera sp.), although three of them had been treated with a 14-day course of fenbendazole.     

Granulocyte plasma membrane damage by leukotoxic supernatant from Pasteurella haemolytica A1 and protection by immune serum.

Bovine respiratory disease caused by Pasteurella haemolytica may be partially mediated by a leukotoxin secreted by the microorganism. We examined the effect of leukotoxic Pasteurella supernatants on leakage of the cytosol enzyme lactate dehydrogenase and the lysosomal enzyme arylsulfatase from bovine granulocytes. Lactate dehydrogenase release (94%) was much higher than arylsulfatase release (38%) over 30 minutes of incubation. The Pasteurella supernatants inhibited superoxide production by stimulated granulocytes at concentrations which also caused substantial cell death as measured by failure to exclude trypan blue. Both toxic effects were prevented by serum from aerosol-immunized calves, and protection appeared to be antibody-specific by comparison with fetal bovine serum or with serum absorbed against intact P. haemolytica. These findings suggest that the leukotoxin may selectively disrupt the granulocyte plasma membrane, and that antibody directed against a surface component of the microorganism is also capable of protecting against the leukotoxin effect.     

Density gradients in a rotating stratified fluid: experimental evidence for a new instability

Velocity gradients induced in a rapidly rotaiting, density-stratified saltwater solution by a slowly rotating disk produce sharp vertical gradients of density, which appear as regularly spaced, curved horizontal sheets when the ratio of angular velocities exceeds a critical value. The existence of the sheets is apparently a finite amplitude manifestationl of a recently proposed viscous instability.