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SYNOPSIS. The effect of H. gallinacea infection on the phagocytic activity of the reticulo-endothelial system in chicks has been investigated. Changes occurring in the pattern of R.E. activity show that there is initial stimulation of phagocytosis within 24 hr and that this increases up to the 4th and 5th days after which time parasites appear in the blood. Thereafter there is a rapid drop in R.E. activity with a proportional increase in parasitaemia following which death ensues. The importance of the protective value of the reticulo-endothelial system is indicated and it is suggested that a toxin produced by the parasites or by their break-down products is the likely cause of phagocytic depression. 相似文献
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RICHARD W. STOFFLE MICHAEL W. TRAUGOTT JOHN V. STONE PAULA D. MCINTYRE FLORENCE V. JENSEN and CARLA C. DAVIDSON 《American anthropologist》1991,93(3):611-635
The concept of a "risk perception shadow" (RPS) has been suggested to describe the geocultural area in which a locally affected population perceives itself to be at risk from a proposed project. Generally such projects involve potentially dangerous substances or activities. The initial conceptualization of an RPS was developed during the social assessment of a proposed Superconducting Super Collider (SSC) in Michigan. This article describes an effort at mapping and analyzing an RPS produced by a proposal to site a low-level radioactive waste (LLRW) storage facility in Michigan. A unique sampling technique was used to define the boundary of the generally concentric RPS. Risk perception mapping (RPM) is suggested as a rapid and efficient method for defining locally affected populations for social impact studies. 相似文献
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Impacts of ozone on forests: a European perspective 总被引:8,自引:1,他引:8
LENA SKÄRBY HELGE RO-POULSEN FLORENCE A. M. WELLBURN & LUCY J. SHEPPARD 《The New phytologist》1998,139(1):109-122
In comparison with the effects of extended drought periods or severe nutrient stress, those of ozone are generally much milder, at least with respect to growth. However, there is substantial evidence from experiments, in the main using young saplings, that O3 does impose a stress on forest trees under European conditions. Decreased chlorophyll contents and photosynthetic rates, changes in carbon allocation, increased antioxidant activity, and reductions in biomass due to O3 have often been recorded, particularly in fast-growing species. Furthermore, 3 appears to weaken the trees' resilience to a range of biotic and abiotic stresses. Interactions between O3 and climatic stress, in particular drought and frost hardiness, are likely to result in potentially detrimental effects.
A link between the occurrence of O3 and forest damage is not unequivocally established in Europe, and the problem remains of extrapolating and/or scaling up from studies on seedlings to predict responses to O3 of mature trees and forest stands, because we know so little about acclimation to O3 . An accurate assessment is also lacking of the magnitude of the O3 effect on European trees both in terms of the forest areas affected and its extent. In this review we suggest that C allocation is the key factor underlying the responses of trees to O3 . Stomata also play a key role, since the acquisition of C must be achieved while an effective control over water consumption is retained. 相似文献
A link between the occurrence of O
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Cryphonectria cubensis, recorded for the first time in India, is responsible for causing severe stem cankers in Eucalyptus grandis in Kerala. Disease outbreaks are localised and vary in severity with host species, at times affecting up to 30% of the trees in a stand. Infection usually occurs on the main stem 1 to 1 ·5 m above ground and occasionally near ground level. There is evidence of tree to tree spread of the disease from the primary infection foci. The disease also affects coppicing by stumps after harvest. Details on the incidence and epidemiology of the disease are presented. 相似文献
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LOÏC HARRAULT BEATRICE ALLARD MICHAEL DANGER FLORENCE MAUNOURY‐DANGER ALEXIS GUILPART GERARD LACROIX 《Freshwater Biology》2012,57(11):2390-2400
1. Sediment plays a key role in internal nutrient cycling and eutrophication in lakes. However, studies focusing on the efficiency of the biomanipulation techniques for improving the control of primary producers have rarely examined the effects of changes in food‐web structure on the sediment biochemical composition and biodegradability. 2. In a 1‐year experiment conducted in large replicated mesocosms, we tested how the absence or presence of a zooplanktivorous fish (roach, Rutilus rutilus) affected the elemental composition and the potential biodegradability of recently deposited sediment in a eutrophic system. The potential biodegradability of these sediments was assessed in laboratory microcosms by measuring the production of CO2 during 44‐day incubations. 3. The potential biodegradability of recently deposited sediment from the fish treatment was 60% higher than that from the fishless treatment. This higher biodegradability was corroborated by a higher annual loss of sediment in fish enclosures (36%) than in fishless ones (16%). Annual losses of carbon, nitrogen and organic phosphorous were higher for sediment from fish enclosures. 4. Carbon and nitrogen contents of sediment were higher for the fish treatment. In contrast, the sediment C/N ratio, one of the proxies used to estimate sediment biodegradability, did not differ between treatments. No relationship was observed between elemental composition of sediment and its potential biodegradability. This latter appeared to be more probably dependent on the biochemical composition of the sediment and especially on the content of labile compounds such as proteins, sugars and polyunsaturated fatty acids. The use of sterols as biomarkers revealed an important degradation by microorganisms of 1‐year‐old sediment from both fish and fishless treatments. 5. Our results revealed that fish biomanipulations might favour clear water states not only through a stronger top–down control on phytoplankton but also through a lower biodegradability of sediment reducing internal nutrient cycling. 相似文献
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