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- ItemOpen AccessThe effect of ultrasound on the root meristem of Zea mays(1973) Hering, Egbert Raymond; Dr.B.J. ShepstoneThe first recorded effect of ultrasound - acoustical waves at a frequency above the audible range - on living organisms was produced by accident over 50 years ago. Chilowsky and Langevin (1916) had been investigating the ability of ultrasonic signals to detect underwater obstacles and had noted that if fish swam into the ultrasonic beam, they were instantly killed. The first deliberate attempt to affect biological material with ultrasound was also destructive; Wood and Loomis (1927) found that ultrasound could produce such diverse effects as the injury and death of small frogs and fish, the disruption of plant cells and protozoa, and the haemolysis of erythrocytes. In research that followed, it was noted that the sensitivities of various organisms are different and that some of the effect, such as partial paralysis, may be reversible. Some of the survival curves obtained in these early experiments were of the kind shown in Figure 1.1, which have the shape characteristic of all or nothing' effect of ultrasound (Grabar, 1953), i.e. a certain minimum sonication time and intensity is necessary to produce an effect. Perhaps the main value of this early work was that it stimulated research into the interaction between ultrasound and l living matter, research which led eventually to the therapeutic use of ultrasound. Gradually it was realised that destruction was only one of the proper11 ties of ultrasonic radiation, and that by careful regulation of the treatment parameters (frequency, intensity, treatment time and pulsing of the radiation) beneficial results could also be achieved (Dyson, Pond, Joseph and Warwick, 1968). Over the past ten years ultrasound has also become well established as the basis of a varied and expanding group of medical diagnostic techniques (Blitz, 1967; Brown and Gordon, 1967), and some misgivings over possible dangers, immediate or delayed, have arisen (Andrew, 1964; Connolly and Pond, 1967; Hill, 1968; Macintosh and Davey, 1970 and 1972). The clinical use of ultrasound has not been preceded by animal experimentation in which the model has been as sensitive as that in the clinical situation, as was the case when X-rays were first introduced as a diagnostic and therapeutic tool in medicine. For X-rays the possibility of any adverse effects was only realised when it was discovered that they were capable of sterilizing guinea pigs without any other obvious change in the well-being of the treated animals (Albers-Schoenberg,1903). However, recent results of animal experimentation, using diagnostic ultrasonic devices, have failed to disclose any deleterious effects (Woodward, Pond and Warwick, 1970; Taylor and Dyson, 1972). The nature and extent of the biological effects are, however, still uncertain (Hill, 1968). It therefore seems important to have a clear understanding of the factors that determine whether any potentially harmful forms of biological change may arise in 12 the course of any of the applications to which ultrasound is being put at present. In parallel with this development a revival has occurred in studies of the mode of biological action of this form of radiation and, at the same time, "it has become apparent that the significance of much of the extensive pioneering work in this field is vitiated by the lack of an adequate system for measuring and reporting physical parameters of irradiation" (Hill, 1970). Since the present studies are on the effects of ultrasound on the root meristem of the maize plant, the next few paragraphs will be devoted to this particular aspect of ultrasound biology.
- ItemOpen Access
- ItemOpen AccessHyperviscosity in the newborn infant: a clinical study(1987) Van der Elst, Clive Willem
- ItemOpen AccessHope, fear, shame, frustration: Continuity and change in the expression of Coloured identity in white supremacist South Africa. 1910-1994(2002) Adhikari, Mohamed; Mendelsohn, RichardThis thesis examines the ways in which Coloured identity manifested itself in South African society from the time the South African state was formed in 1910 till the institution of democratic rule in 1994. The central argument of the dissertation is that Coloured identity is better understood, not as having evolved through a series of transformations during this period, as conventional historical thinking would have it, but to have remained remarkably stable throughout the era of white rule. This is not to contend that Coloured identity was static or that it lacked fluidity but that the continuities during this period were more fundamental to the way in which it operated as a social identity than the changes it experienced. It is argued that this stability was derived from a central core of enduring characteristics that regulated the way in which Colouredness functioned as an identity during this period. Each of the four emotions in the title of the thesis corresponds to a key characteristic at the heart of the identity. The principal constituents of this stable core are the assimilationism of the Coloured people (hope), their intermediate status in the racial hierarchy (fear), the negative connotations, especially that of racial hybridity, with which it was imbued (shame), and finally, the marginality of the Coloured community (frustration). In addition to a series of thematic analyses that broadly encompass the expression of Coloured identity throughout the era of white supremacist rule, the dissertation uses a range of case studies of key texts to demonstrate its thesis. Collectively, the case studies have been chosen to cover the entire period under review as well as to represent the full spectrum of opinion within the Coloured community about the nature of their identity. After an opening chapter that sets the social and historical context and that maps out its conceptual framework, the thesis outlines a historiography of Coloured writing on the history of their community. This analysis provides an overview of changing perceptions within the Coloured community of their history and nature as a social group. The first two case studies, the APO (1909-1923) and the Educational Journal (1915-1940), investigate the expression of Coloured identity in the earlier decades of South Africa's existence. The second set of case histories, Torch (1946-1963) and A Walk in the Night (1962), explore new perspectives introduced by the emergence of a radical movement in Coloured politics during the middle decades of white rule. In the next chapter the Black Consciousness poetry of James Matthews (1970s) and South (1987-1994) serve as examples of opinion within the anti-apartheid movement during the latter phases of the apartheid era. Finally, an examination of Hein Willemse's 1993 study of the Straatpraatjes column, published in the APO from 1909 onwards, is used in the conclusion to illustrate a particular view common at the close of the apartheid period and to reinforce the general conclusions of the thesis.
- ItemOpen AccessGamma irradiation of fruits(1984) Beyers, Marguerite; Van Der Linde, H J; Irving, H.M.N.H.At a Joint FAO/tAEA/WHO Expert Committee on Food Irradiation (JECFI) meeting held in 1976, recommendations were made to rationalize the unnecessarily elaborate wholesomeness. evaluation procedures for irradiated foodstuffs: inter a/ia, that (a) for irradiation doses up to 5 kGy, radiation-chemical results together with animal feeding studies would eventually lead to the general acceptance of irradiated food, (b) wholesomeness data could be extrapolated from a representative foodstuff to foods in the same diet class, and (c) a purely chemical approach to wholesomeness evaluation would be contemplated if enough data could be accumulated. Following these guidelines, a chemical investigation into the wholesomeness of y-irradiated fruit with special emphasis on the mango was undertaken. Irradiation at the commercially recommended doses did not adversely affect the constituents of mangoes. papayas, litchis and strawberries at the edible-ripe stage, nor could changes which could be attributed to irradiation be detected in irradiated mangoes and papayas as the fruits ripened. The conventional preservation method of canning and the storage of frozen fruit were more detrimental to the nutritional value of the fruits than irradiation. The chemical composition of the four fruits was sufficiently similar for them to be grouped into the same diet class. These favourable radiation-chemical results justified the development of a theoretical model mango which could be used for extrapolation of wholesomeness data from an individual fruit species to all others within the same diet class. Several mathematical models of varying orders of sophistication were evolved. In all of them, it was assumed that the radiant energy entering the system reacted solely with water. The extent of the reaction of the other components of the model fruit with the primary water radicals was then determined. No matter which mathematical treatment was employed, it was concluded that the only components which would undergo significant modification would be the sugars. Furthermore, by the application of radiation-chemical knowledge to these results, the only toxic radiolysis products formed in significant quantities would be the carbonyls derived from the sugars, but these carbonyls would be nonmutagenic in the fruit. These predictions were verified experimentally in the so-called "synthetic" mango (an aqueous solution of the components of the model mango) and in Kent mangoes both as to carbonyl yields and carbonyl nonmutagenicity in the fruits and as to the protective influence of the sugars on the degradative behaviour of certain selected components of the mango. In order to extrapolate these data from the mango to other fruits, mathematical models of three fruits containing less sugar than the mango, viz. the strawberry, tomato and lemon, were compiled. With these models, the conclusion was reached that the theoretical degradation spectra of these fruits were qualitatively similar to the degradation pattern of the model mango. The protective effect of the sugars diminished with decreasing sugar concentration. No additional mutagenic radiolysis products were predicted. It was also estimated that the radiolysis products would be nontoxic. Theory was again substantiated by the practical demonstration of the protective effect of the sugars in the tomato and lemon. The decrease in radiation damage was enhanced by the mutu.a.1 protection of the components of the whole synthetic fruits with ultimate protection being afforded by the biological systems of the real fruits. Therefore, the radiation-chemical behaviour of fruits was essentially similar, so that extrapolation of wholesomeness data from one fruit to another would be possible. This "chemiclearance" concept formed part of the evidence which enabled the 1981 JECFI meeting to arrive at the conclusion that the irradiation of any food commodity up to 1 0 kGy presents no toxicological hazard, so that toxicological testing of such foods would no longer be necessary.