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dc.contributor.advisorTolson, Homer
dc.creatorBerry, Michael Josep
dc.descriptionTypescript (photocopy).en
dc.description.abstractFor over five decades it was thought that aphids transmitted nonpersistent phytopathogenic viruses in what has been termed a "stylet-borne" manner. More recently, it has been proposed that aphids transmit virus as a result of "ingestion and egestion" of virus-containing plant sap. In the former case, virus is acquired and carried as a contaminant in the distal portion of the stylets. Ingestion-egestion, on the other hand, provides that virus is carried up to the maxillary food canal of the alimentary canal and perhaps beyond the pharyngeal gustatory organ. In the latter case there is greater opportunity for interaction between virus and both living and nonliving surfaces within the aphid. When the rate of loss of infectivity of MDMV (maize dwarf mosaic virus) was studied, early results suggested that both ingestion-egestion and stylet-borne contamination were operative mechanisms, the degree to which one predominates depending on the length of the acquisition period. Short acquisition times would result in aphids transmitting virus primarily because of stylet-borne contamination, whereas long acquisition times should result in primarily ingestion-egestion of virus-containing plant sap. Results indicate that the rate of loss of infectivity is independent of acquisition access time. There is a maximal amount of virus that can be acquired by aphids. The hypothesis that a dual-mechanistic approach can explain nonpersistent transmission is not supported. Nonlinear regression analyses can provide good predictions of transmission efficiency after extended retention time intervals. Possible implications of these findings are discussed. The purpose of this investigation was to determine differences in cardiovascular adjustments following exposure to an altitude of 2,300 meters, 2,560 meters or 2,900 meters. Specific purposes of this investigation were to determine the effects of exposure to one of the above altitudes on the following variables: hemoglobin concentration, red blood cell count, systolic blood pressure, diastolic blood pressure and resting heart rate. Subjects for this investigation were 14 male members of the "Glaciers of the Canadian Rockies, 82" expedition and the two principal investigators. Subjects were measured in order to determine the initial value for the physiological variables of interest prior to being taken to altitude. Subjects were measured again in order to determine final values following 12 to 14 days of exposure to altitude....en
dc.format.extentix, 108 leaves ;en
dc.rightsThis thesis was part of a retrospective digitization project authorized by the Texas A&M University Libraries. Copyright remains vested with the author(s). It is the user's responsibility to secure permission from the copyright holder(s) for re-use of the work beyond the provision of Fair Use.en
dc.subjectPhysical Educationen
dc.subject.classification1983 Dissertation B534
dc.subject.lcshAltitude, Influence ofen
dc.subject.lcshCardiovascular systemen
dc.titleHematological changes in response to exposure to moderate altitudesen
dc.typeThesisen A&M Universityen of Philosophyen D. in Philosophyen
dc.contributor.committeeMemberAnderson, James, Jr.
dc.contributor.committeeMemberChevrette, John
dc.contributor.committeeMemberJessup, George T.
dc.format.digitalOriginreformatted digitalen
dc.publisher.digitalTexas A&M University. Libraries

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