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The eclipse phase of vaccinia virus growing in chick embryo cell monolayers and some technical procedures which affect its demonstration
- R. Postlethwaite, H. B. Maitland
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- Journal:
- Journal of Hygiene / Volume 58 / Issue 2 / June 1960
- Published online by Cambridge University Press:
- 15 May 2009, pp. 133-145
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1. When chick embryo cell monolayers were infected with ultrasonically treated elementary body suspension by a short period of adsorption some of the adsorbed virus lost infectivity in a few minutes. This was followed by a more gradual loss during incubation of the cultures. The lowest point was reached at 4–6 hr. followed by a rise in titre due to production of new virus at 7–8 hr. The quantitative assessment of these changes is discussed.
2. In such cultures, titration of intact and disintegrated cells after incubation for 4–5 hr., indicated an eclipse phase by showing an absence of infective virus in cells which ultimately produced it. The process of eclipse continued for several hours. With inoculum that had not been subjected to ultrasonic treatment it was not possible to show this by infecting HeLa cell monolayers.
3. Ultrasonically treated inoculum, compared with a similar, but untreated inoculum, had a three to flvefold higher titre. The virus units in it were more uniformly capable of infecting cells. After its adsorption to monolayers a rapid loss of some infective virus occurred within a few minutes which was not demonstrable with untreated inoculum. During incubation of monolayers infected with treated inoculum the loss of infectivity was faster, there was a more rapid production of new virus and a greater yield. The nature of the changes in the virus which were brought about by ultrasonic treatment have not been explained, but the use of such an inoculum markedly affected the results of experiments.
4. Treatment of infected monolayers with trypsin or EDTA caused the cells to shed as much as half their virus. This virus would not be released spontaneously into the medium or removed from monolayers by washing. This applied to all periods of incubation up to 24 hr. or more when marked increase of virus had occurred.
5. The disintegration of infected cells by ultrasonic treatment was efficient in releasing infective virus from them, although it was not possible to be certain all the virus in the cells was rendered detectable by this technique.
6. The effect of some technical procedures on the interpretation of results is discussed.
Features of molluscum contagiosum in the north-east of Scotland and in Fijian village settlements
- R. Postlethwaite, J. A. Watt, T. G. Hawley, I. Simpson, Helen Adam
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- Journal:
- Journal of Hygiene / Volume 65 / Issue 3 / September 1967
- Published online by Cambridge University Press:
- 15 May 2009, pp. 281-291
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Between 1964 and 1966 comparative studies were carried out in Aberdeen, Scotland, and in village settlements in Fiji on the clinico-epidemiological features of molluscum contagiosum. In Aberdeen there was a positive correlation between this disease and attendance of patients at public swimming baths. The preponderance of male patients in Aberdeen was attributed to their more frequent indulgence in swimming. Household spread of the condition was rare in Aberdeen but common in Fiji. Lesions frequently occurred unilaterally or were situated on opposing skin surfaces. They were mainly central in distribution in Aberdeen, the axilla being a site of predilection. In Fijians, peripheral lesions were fairly common though palms and soles were not affected. Peak age incidence in Aberdeen was 10–12 years, contrasting with a peak at 2–3 years in Fiji. Opportunity for contagious exposure appeared to be the main factor determining transmission of molluscum contagiosum between hosts, this opportunity occurring frequently and early in life in Fiji but only under special circumstances and later in childhood in Aberdeen. However, the age distributions in the two populations suggested the possible operation of immunological as well as environmental factors in determining the overall pattern of disease in the community.
We should like to express our thanks to the following people whose support and co-operation made this joint study possible: Dr K. J. Gilchrist, Principal of the Fiji School of Medicine; Prof J. A. R. Miles, Department of Microbiology, University of Otago; Dr C. H. Gurd, Director of Medical Services, Fiji; and Prof. A. Macdonald, Department of Bacteriology, University of Aberdeen. We are indebted to Dr T. E. Anderson and Dr R. A. Main of the Aberdeen Royal Infirmary for referring patients, to Mr W. Hodgkiss of the Torry Research Station, Aberdeen for carrying out the electron microscopy and to Dr Peter Bennett, Nuffield Foundation Scholar in Tropical Medicine from Aberdeen in 1962, who brought to the attention of the Aberdeen workers the prevalence of molluscum contagiosum in Fiji. Part of the work was supported by a grant to R. Postlethwaite from the British Empire Cancer Campaign for Research. Mr (now Dr) Ian Simpson and Miss Helen Adam were supported by Nuffield Foundation Scholarships in Tropical Medicine, and Dr J. A. Watt by a Garden Research Fellowship from the University of Aberdeen.
Multi-layer hydraulic exchange flows
- G. F. LANE-SERFF, D. A. SMEED, C. R. POSTLETHWAITE
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- Journal:
- Journal of Fluid Mechanics / Volume 416 / 10 August 2000
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- 10 August 2000, pp. 269-296
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Flows between ocean basins are often controlled by narrow channels and shallow sills. A multi-layer hydraulic control theory is developed for exchange flow through such constrictions. The theory is based on the inviscid shallow-water equations and extends the functional approach introduced by Gill (1977) and developed by Dalziel (1991). The flows considered are those in rectangular–cross-section channels connecting two large reservoirs, with a single constriction (sill and/or narrows). The exchange flow depends on the stratification in the two reservoirs, represented as a finite number of immiscible layers of (different) uniform density. For most cases the flow is ‘controlled’ at the constriction and often at other points along the channel (virtual controls) too. As with one- and two-layer hydraulics, controls are locations at which the flow passes from one solution branch to another, and at which (at least) one internal wave mode is stationary. The theory is applied to three-layer flows, which have two internal wave modes, predicting interface heights and layer fluxes from the given reservoir conditions. The theoretical results for three-layer flows are compared to a comprehensive set of laboratory experiments and found to give good agreement. The laboratory experiments also show other features of the flow, such as the formation of waves on the interfaces. The implications of the results for oceanographic flows and ocean modelling are discussed.