Hugo Raes : de roman als montage : een struktuuranalyse van De vadsige koningen, Een faun met kille horentjes en, Het smarán, het vikka, de ronko en al de andere kleuren van de geschiedenis
- Authors: Renders, L E M M E
- Date: 1981
- Subjects: Raes, Hugo -- Criticism and interpretation Raes, Hugo -- De vadsige koningen Raes, Hugo -- Een faun met kille horentjes Raes, Hugo -- Het smarán, het vikka, de ronko en al de andere kleuren van de geschiedenis Dutch fiction -- 20th century -- History and criticism
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3623 , http://hdl.handle.net/10962/d1007493
- Description: De analyse van het individuele literaire werk zal steeds het begin- en eindpunt moeten zijn van de literatuurstudie in welke gedaante dan ook: "Dit neemt echter niet weg dat het begin en einde, het alfa en omega van de literaire bedrijvigheid, het literair kunstwerk als zodanig, de literaire intentie, functie en efficientie de literair, literairesthetisch, te actualiseren en te valoriseren tekst is ... " (Rutten, 1973, p.144). Juist deze vorm van onderzoek lijkt op het ogenblik soms weI eens verloren te raken tussen de veelheid van literaire theorieen die overal opgang maken. De beoefenaars van de literaire kritiek lijken dikwijls meer begaan met het opbouwen en afbreken van theorieen dan met het literaire werk zelf. Sinds W. Bloks studie Verhaal en lezer in 1960 voor het eerst het licht zag, mag er dan op het gebied van de literatuurwetenschap in de Nederlanden en daarbuiten heel wat veranderd zijn, maar zijn uitspraak: " ... dat de romantheorie op het ogenblik het meest gebaat is met analyses van afzonderlijke werken" (1969, p.9) heeft zeker nog niets aan geldigheid ingeboet.
- Full Text:
- Date Issued: 1981
- Authors: Renders, L E M M E
- Date: 1981
- Subjects: Raes, Hugo -- Criticism and interpretation Raes, Hugo -- De vadsige koningen Raes, Hugo -- Een faun met kille horentjes Raes, Hugo -- Het smarán, het vikka, de ronko en al de andere kleuren van de geschiedenis Dutch fiction -- 20th century -- History and criticism
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3623 , http://hdl.handle.net/10962/d1007493
- Description: De analyse van het individuele literaire werk zal steeds het begin- en eindpunt moeten zijn van de literatuurstudie in welke gedaante dan ook: "Dit neemt echter niet weg dat het begin en einde, het alfa en omega van de literaire bedrijvigheid, het literair kunstwerk als zodanig, de literaire intentie, functie en efficientie de literair, literairesthetisch, te actualiseren en te valoriseren tekst is ... " (Rutten, 1973, p.144). Juist deze vorm van onderzoek lijkt op het ogenblik soms weI eens verloren te raken tussen de veelheid van literaire theorieen die overal opgang maken. De beoefenaars van de literaire kritiek lijken dikwijls meer begaan met het opbouwen en afbreken van theorieen dan met het literaire werk zelf. Sinds W. Bloks studie Verhaal en lezer in 1960 voor het eerst het licht zag, mag er dan op het gebied van de literatuurwetenschap in de Nederlanden en daarbuiten heel wat veranderd zijn, maar zijn uitspraak: " ... dat de romantheorie op het ogenblik het meest gebaat is met analyses van afzonderlijke werken" (1969, p.9) heeft zeker nog niets aan geldigheid ingeboet.
- Full Text:
- Date Issued: 1981
The elements of job evaluation in the development of a pay structural comparison system guide to conducting compensation surveys to determine competitive adjustments to base salary ranges
- Authors: Snelgar, Robin John
- Date: 1981
- Subjects: Wage surveys , Job evaluation , Job analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3118 , http://hdl.handle.net/10962/d1004726
- Description: If the wage policy of an organisation is to remain competitive in the labour market, that is, pay rates that are at least approximately equal to those prevailing in the community, then it must collect accurate wage and salary data in order to alter its pay structure as may become necessary. Wage and salary survey information provides a means by which management can determine whether its entire wage level is in accordance with that of the external labour market, and thus it is absolutely essential that methods and techniques utilised to collect such information are as objective and accurate as possible. The vital factor which has been revealed by the utilisation of many existing wage and salary survey guides is that the unavoidable subjectivity involved in the basic techniques utilised in survey procedures tends to have a cumulative effect on both data collection and analysis, and ultimately interpretation. As each technique is utilised, whether it be to obtain job comparability or to adjust salary data, the overall level of subjectivity is increased, which results in a cumulative increase in the margin of error involved in data collection. This study has been aimed at developing and practically testing a comprehensive guide to conducting wage and salary surveys which effectively minimises and, over successive surveys, eradicates the necessity for these subjective techniques. Due to the fact that the elements of job evaluation, namely, job analysis, job description, job specification and the job evaluation plan itself, form the nucleus of the techniques utilised for the data gathering and analysis process, the initial study was aimed at developing a job evaluation process which would be as objective as possible. In the development of such a system a range of job evaluation plans were tested for comparability in rating of jobs, the hypothesis being that any evaluation method or plan, when correctly applied to a series of jobs, will result in the same classification. This study intercorrelated rates derived for twenty-four key jobs selected from one particular organisation, using the job evaluation methods utilised by sixteen different organisations, and found that these rates intercorrelated between 0,93 to 0,99. These intercorrelations indicate a high degree of commonality among the sixteen methods; thus providing a justification for the utilisation of one particular job evaluation plan for the adjustment and weighing of wage and salary data in the survey data analysis procedure. To further justify the utilisation of one particular method, and thereby increase probability of acceptance by participating organisations, the independence of the sub-factors of the selected plan were tested by intercorrelating the factor scores for two job samples, one consisting of sixty jobs, type and level being heterogeneous, the other consisting of forty jobs, type and level being homogeneous. Sub-factor intercorrelations in the group of heterogeneous jobs ranged from 0,71 to 0,98 while all but one correlated at or above 0,90 with the total score, thus emphasising the independence of sub-factors, while intercorrelations in the group of homogeneous sample were much lower, ranging from 0,26 to 0,89, indicating greater factorial independence due to the fact that these jobs are limited to a narrower range of grades such that specific job differences in respect of sub-factors are more likely to show up. Utilising this selected job evaluation plan as the core of the developed job evaluation process, a wage and salary survey guide was formulated, the unique concept being a comparison of participating organisation pay structures rather than comparison of positions as a basis for data collection. The job evaluation system was utilised in the formulation of a "one-time" standardisation of participating organisation pay structures according to the survey organisation pay structure, the hypothesis being that these standardised pay structures may be utilised over successive surveys without the necessity for restandardisation, and thus eliminating the use of subjective methods and techniques subsequent to the initial standardisation. Utilising an international oil company as the survey organisation this newly formulated structural comparison guide was practically tested by applying it in conjunction with the existing survey organisation wage and salary survey guide as a means of competitive market wage and salary data gathering and analysis, over successive survey years, namely, 1974, 1977, and 1980. The results obtained through application of this guide were subsequently compared with those results obtained by two professional survey organisations, and proved to be reliable and consistent enough over the applicable survey years to warrant acceptance of the pay structural comparison concept as a valid wage and salary survey technique.
- Full Text:
- Date Issued: 1981
- Authors: Snelgar, Robin John
- Date: 1981
- Subjects: Wage surveys , Job evaluation , Job analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3118 , http://hdl.handle.net/10962/d1004726
- Description: If the wage policy of an organisation is to remain competitive in the labour market, that is, pay rates that are at least approximately equal to those prevailing in the community, then it must collect accurate wage and salary data in order to alter its pay structure as may become necessary. Wage and salary survey information provides a means by which management can determine whether its entire wage level is in accordance with that of the external labour market, and thus it is absolutely essential that methods and techniques utilised to collect such information are as objective and accurate as possible. The vital factor which has been revealed by the utilisation of many existing wage and salary survey guides is that the unavoidable subjectivity involved in the basic techniques utilised in survey procedures tends to have a cumulative effect on both data collection and analysis, and ultimately interpretation. As each technique is utilised, whether it be to obtain job comparability or to adjust salary data, the overall level of subjectivity is increased, which results in a cumulative increase in the margin of error involved in data collection. This study has been aimed at developing and practically testing a comprehensive guide to conducting wage and salary surveys which effectively minimises and, over successive surveys, eradicates the necessity for these subjective techniques. Due to the fact that the elements of job evaluation, namely, job analysis, job description, job specification and the job evaluation plan itself, form the nucleus of the techniques utilised for the data gathering and analysis process, the initial study was aimed at developing a job evaluation process which would be as objective as possible. In the development of such a system a range of job evaluation plans were tested for comparability in rating of jobs, the hypothesis being that any evaluation method or plan, when correctly applied to a series of jobs, will result in the same classification. This study intercorrelated rates derived for twenty-four key jobs selected from one particular organisation, using the job evaluation methods utilised by sixteen different organisations, and found that these rates intercorrelated between 0,93 to 0,99. These intercorrelations indicate a high degree of commonality among the sixteen methods; thus providing a justification for the utilisation of one particular job evaluation plan for the adjustment and weighing of wage and salary data in the survey data analysis procedure. To further justify the utilisation of one particular method, and thereby increase probability of acceptance by participating organisations, the independence of the sub-factors of the selected plan were tested by intercorrelating the factor scores for two job samples, one consisting of sixty jobs, type and level being heterogeneous, the other consisting of forty jobs, type and level being homogeneous. Sub-factor intercorrelations in the group of heterogeneous jobs ranged from 0,71 to 0,98 while all but one correlated at or above 0,90 with the total score, thus emphasising the independence of sub-factors, while intercorrelations in the group of homogeneous sample were much lower, ranging from 0,26 to 0,89, indicating greater factorial independence due to the fact that these jobs are limited to a narrower range of grades such that specific job differences in respect of sub-factors are more likely to show up. Utilising this selected job evaluation plan as the core of the developed job evaluation process, a wage and salary survey guide was formulated, the unique concept being a comparison of participating organisation pay structures rather than comparison of positions as a basis for data collection. The job evaluation system was utilised in the formulation of a "one-time" standardisation of participating organisation pay structures according to the survey organisation pay structure, the hypothesis being that these standardised pay structures may be utilised over successive surveys without the necessity for restandardisation, and thus eliminating the use of subjective methods and techniques subsequent to the initial standardisation. Utilising an international oil company as the survey organisation this newly formulated structural comparison guide was practically tested by applying it in conjunction with the existing survey organisation wage and salary survey guide as a means of competitive market wage and salary data gathering and analysis, over successive survey years, namely, 1974, 1977, and 1980. The results obtained through application of this guide were subsequently compared with those results obtained by two professional survey organisations, and proved to be reliable and consistent enough over the applicable survey years to warrant acceptance of the pay structural comparison concept as a valid wage and salary survey technique.
- Full Text:
- Date Issued: 1981
The liturgies of Guillaume Farel: their meaning and relevance
- Authors: Kaltenrieder, Andre Emile
- Date: 1981
- Subjects: Farel, Guillaume, 1489-1565 Liturgics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1224 , http://hdl.handle.net/10962/d1004540
- Description: Relatively little study has been devoted to Guillaume Farel. Though a number of Biographies have been published, these were mainly devotional or inspirational. The only critical biography to have been published in modern times, and to which the author has made much reference, is that written by the 'FAREL COMMITTEE' to commemorate the fourth centenary of the reformation at Neuchȃtel. The comparative neglect suffered by Farel and his works is surprising in view of his role as pioneer of the reformation in French-speaking Churches. The spotlight has been held almost exclusively on the second generation reformer John Calvin. The paucity of material available may help explain why Farel has remained such an obscure figure. This dissertation does not attempt to bring to light the full scope of Farel's work. This still has to be done. Incidentally the author has been informed that. there are at present two American post-graduate students doing research on Farel at Neuchȃtel. This may hold a promise of further light on this significant father of the reformation. The author has limited himself here to an examination and evaluation of Farel's liturgical works. These were only a very small portion of his wide field of activity. The further study necessary to investigate the full influence of these liturgies on the development of reformed worship is only outlined here. In order to set the Farellian orders in their context, a certain amount of historical and doctrinal background has been given. This is by no means exhaustive as each service would justify a separate dissertation. An effort has been made to cut background down to a minimum and to bring out the main tendencies only so as to situate Farel in the development of the understanding of the Church 's worship. (Preface)
- Full Text:
- Date Issued: 1981
- Authors: Kaltenrieder, Andre Emile
- Date: 1981
- Subjects: Farel, Guillaume, 1489-1565 Liturgics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1224 , http://hdl.handle.net/10962/d1004540
- Description: Relatively little study has been devoted to Guillaume Farel. Though a number of Biographies have been published, these were mainly devotional or inspirational. The only critical biography to have been published in modern times, and to which the author has made much reference, is that written by the 'FAREL COMMITTEE' to commemorate the fourth centenary of the reformation at Neuchȃtel. The comparative neglect suffered by Farel and his works is surprising in view of his role as pioneer of the reformation in French-speaking Churches. The spotlight has been held almost exclusively on the second generation reformer John Calvin. The paucity of material available may help explain why Farel has remained such an obscure figure. This dissertation does not attempt to bring to light the full scope of Farel's work. This still has to be done. Incidentally the author has been informed that. there are at present two American post-graduate students doing research on Farel at Neuchȃtel. This may hold a promise of further light on this significant father of the reformation. The author has limited himself here to an examination and evaluation of Farel's liturgical works. These were only a very small portion of his wide field of activity. The further study necessary to investigate the full influence of these liturgies on the development of reformed worship is only outlined here. In order to set the Farellian orders in their context, a certain amount of historical and doctrinal background has been given. This is by no means exhaustive as each service would justify a separate dissertation. An effort has been made to cut background down to a minimum and to bring out the main tendencies only so as to situate Farel in the development of the understanding of the Church 's worship. (Preface)
- Full Text:
- Date Issued: 1981
An ecophysiological study of the effects of changes in salinity and temperature on the distribution of Macrobrachium Petersi (Hilgendorf) in the Keiskamma river and estuary
- Read, Graeme Hamilton Leonard
- Authors: Read, Graeme Hamilton Leonard
- Date: 1982
- Subjects: Macrobrachium -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5804 , http://hdl.handle.net/10962/d1006304
- Description: Summary: The distribution of adult, juvenile, post larval and larval Macrobrachium petersi (Hilgendorf) was studied in relation to temperature and salinity in the Keiskamma river and estuary from May 1979 to May 1981. M. petersi is a subtropical species, which confined activity of all stages in the field to the summer months. Variable freshwater discharge and tidal effects determined the salinity and temperature profiles in the middle and upper reaches of the Keiskamma estuary. Thus, a dry 1979/80 summer and a wet 1980/81 summer markedly influenced the abundance and distribution of adult M. petersi in the river and estuary respectively. Adult M. petersi migrate to the estuary under flooding conditions and upstream in response to elevated salinities. Although M. petersi has nine larval stages only a preponderance of stage I were caught in the field. These portray a distinct nocturnal and diurnal distribution pattern which is influenced by salinity, especially under stratified conditions. After flooding the larvae show an affinity for salt front regions and reach these by remaining in the water column on the ebbing tide. A substantial drop in abundance downstream from the salt front suggests that the larvae loose their planktonic phase which is an effective retention mechanism, and confines larval development to the middle and upper reaches of the estuary. Post larvae were caught towards the end of the 1981 breeding season which indicates that complete larval development takes place in the estuary. A post larval migration to freshwater, which reaches a peak in February and March, was monitored. Thus both the freshwater and estuarine environments form an inseparable link in the life cycle of M. petersi. The distribution of stage I larvae in the Keiskamma estuary suggested that salinity played a role in development. The fact that other larval stages were not found emphasised the necessity for a quantitative laboratory investigation to determine the importance of salinity in the developmental history of M. petersi larvae and post larvae. However, the modifying influence of temperature could not be ignored so a multivariable approach was adopted. This, together with a surface response technique, aided the interpretation of the effect of a variety of combinations of salinity and temperature on ecdysis to stage II, larval survival and requirements for metamorphosis to post larvae. It was estimated that the minimum salinity requirement for complete larval development, within a temperature range from 18 to 30⁰C was 8%₀, although ecdysis to stage II and metamorphosis to post larvae could occur in salinities less than this value. Despite the euryhalinity of the larvae, the behaviour of adult M. petersi to an increase in salinity and the affinity of stage I larvae to salt front regions restricted development to the upper reaches of the estuary. This is discussed as an adaptation which not only ensures retention within the estuary but favours recruitment to the adult population in freshwater. The osmoregulatory patterns of larval, post larval, juvenile and adult M. petersi correlated with their distribution. These were approximated by a cubic polynomial which enabled the different patterns to be compared. The larval stages investigated (I, II, V & IX) displayed a remarkable capacity to regulate which was strongest in stage I as these could regulate in both freshwater and 35%₀. The ability to regulate in freshwater was lost hereafter but regained in the post larvae, which also regulated in 35%₀. Juveniles (caught at the ebb and flow) displayed a similar regulatory pattern to the adults and "hyposmoconformed" in salinities beyond the isosmotic point as the need to regulate in 35%₀ was no longer necessary. The osmoregulatory capacity of M. petersi larvae in relation to other decapod larvae is discussed. Marine transport of the euryhaline larval and post larval stages accounts for the distribution of M. petersi along the South African coastline. However, south of 31°S latitude the sea-surface temperature decreases abruptly. This region coincides with the southern limit of the distribution of M. petersi. Although larval M. petersi can tolerate high salinity (35%₀) in combination with low temperature, the post larvae cannot, which is likely to account for their restricted southern distribution. The genus Macrobrachium are in the process of invading freshwater. The possible course that this might have taken has been discussed in the light of available evidence as well as the findings of this study.
- Full Text:
- Date Issued: 1982
- Authors: Read, Graeme Hamilton Leonard
- Date: 1982
- Subjects: Macrobrachium -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5804 , http://hdl.handle.net/10962/d1006304
- Description: Summary: The distribution of adult, juvenile, post larval and larval Macrobrachium petersi (Hilgendorf) was studied in relation to temperature and salinity in the Keiskamma river and estuary from May 1979 to May 1981. M. petersi is a subtropical species, which confined activity of all stages in the field to the summer months. Variable freshwater discharge and tidal effects determined the salinity and temperature profiles in the middle and upper reaches of the Keiskamma estuary. Thus, a dry 1979/80 summer and a wet 1980/81 summer markedly influenced the abundance and distribution of adult M. petersi in the river and estuary respectively. Adult M. petersi migrate to the estuary under flooding conditions and upstream in response to elevated salinities. Although M. petersi has nine larval stages only a preponderance of stage I were caught in the field. These portray a distinct nocturnal and diurnal distribution pattern which is influenced by salinity, especially under stratified conditions. After flooding the larvae show an affinity for salt front regions and reach these by remaining in the water column on the ebbing tide. A substantial drop in abundance downstream from the salt front suggests that the larvae loose their planktonic phase which is an effective retention mechanism, and confines larval development to the middle and upper reaches of the estuary. Post larvae were caught towards the end of the 1981 breeding season which indicates that complete larval development takes place in the estuary. A post larval migration to freshwater, which reaches a peak in February and March, was monitored. Thus both the freshwater and estuarine environments form an inseparable link in the life cycle of M. petersi. The distribution of stage I larvae in the Keiskamma estuary suggested that salinity played a role in development. The fact that other larval stages were not found emphasised the necessity for a quantitative laboratory investigation to determine the importance of salinity in the developmental history of M. petersi larvae and post larvae. However, the modifying influence of temperature could not be ignored so a multivariable approach was adopted. This, together with a surface response technique, aided the interpretation of the effect of a variety of combinations of salinity and temperature on ecdysis to stage II, larval survival and requirements for metamorphosis to post larvae. It was estimated that the minimum salinity requirement for complete larval development, within a temperature range from 18 to 30⁰C was 8%₀, although ecdysis to stage II and metamorphosis to post larvae could occur in salinities less than this value. Despite the euryhalinity of the larvae, the behaviour of adult M. petersi to an increase in salinity and the affinity of stage I larvae to salt front regions restricted development to the upper reaches of the estuary. This is discussed as an adaptation which not only ensures retention within the estuary but favours recruitment to the adult population in freshwater. The osmoregulatory patterns of larval, post larval, juvenile and adult M. petersi correlated with their distribution. These were approximated by a cubic polynomial which enabled the different patterns to be compared. The larval stages investigated (I, II, V & IX) displayed a remarkable capacity to regulate which was strongest in stage I as these could regulate in both freshwater and 35%₀. The ability to regulate in freshwater was lost hereafter but regained in the post larvae, which also regulated in 35%₀. Juveniles (caught at the ebb and flow) displayed a similar regulatory pattern to the adults and "hyposmoconformed" in salinities beyond the isosmotic point as the need to regulate in 35%₀ was no longer necessary. The osmoregulatory capacity of M. petersi larvae in relation to other decapod larvae is discussed. Marine transport of the euryhaline larval and post larval stages accounts for the distribution of M. petersi along the South African coastline. However, south of 31°S latitude the sea-surface temperature decreases abruptly. This region coincides with the southern limit of the distribution of M. petersi. Although larval M. petersi can tolerate high salinity (35%₀) in combination with low temperature, the post larvae cannot, which is likely to account for their restricted southern distribution. The genus Macrobrachium are in the process of invading freshwater. The possible course that this might have taken has been discussed in the light of available evidence as well as the findings of this study.
- Full Text:
- Date Issued: 1982
An evaluation of the effects of imported insects on the weed Lantana camara L. in South Africa
- Authors: Cilliers, Catharina Johanna
- Date: 1982
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5808 , http://hdl.handle.net/10962/d1006853
- Description: The plant, Lantana camara L. (V erbenaceae), is a weed in tropical and subtropical areas around the world. In many countries, including South Africa, biological control of this weed has been attempted. Although 12 insect species have been imported into South Africa, only four species established and these are dealt with in this study. Ophiomyia lantanae Diptera: Agromyzidae, a seed fly, is briefly dealt with; the main emphasis is on the leaf damaging species Teleonemia scrupulosa Stål (Hemiptera: Tingidae) and two leaf mining beetles, Octotoma scabripennis Guerin and Uroplata girardi Pic . (Hispidae: Coleoptera). In evaluating the insect damage to lantana leaves, monthly samples of branches were taken over three seasons from 1977- 80. This destructive sampling allowed the study of population build-up of the insects. In addition, counts were made of the numbers of damaged and healthy leaves, flowers and seeds and the damage related to the activities of the different stages of the hispids and the tingid. Insect exclusion experiments were also used to determine the effect of the insects on the growth of L. camara. The results reported in this thesis clearly indicate that the imported natural enemies retard L. camara growth and vigour and the effects are manifested in a marked reduction in stem diameter, internodal length, leaf size, leaf lifespan and in flower and seed set.
- Full Text:
- Date Issued: 1982
- Authors: Cilliers, Catharina Johanna
- Date: 1982
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5808 , http://hdl.handle.net/10962/d1006853
- Description: The plant, Lantana camara L. (V erbenaceae), is a weed in tropical and subtropical areas around the world. In many countries, including South Africa, biological control of this weed has been attempted. Although 12 insect species have been imported into South Africa, only four species established and these are dealt with in this study. Ophiomyia lantanae Diptera: Agromyzidae, a seed fly, is briefly dealt with; the main emphasis is on the leaf damaging species Teleonemia scrupulosa Stål (Hemiptera: Tingidae) and two leaf mining beetles, Octotoma scabripennis Guerin and Uroplata girardi Pic . (Hispidae: Coleoptera). In evaluating the insect damage to lantana leaves, monthly samples of branches were taken over three seasons from 1977- 80. This destructive sampling allowed the study of population build-up of the insects. In addition, counts were made of the numbers of damaged and healthy leaves, flowers and seeds and the damage related to the activities of the different stages of the hispids and the tingid. Insect exclusion experiments were also used to determine the effect of the insects on the growth of L. camara. The results reported in this thesis clearly indicate that the imported natural enemies retard L. camara growth and vigour and the effects are manifested in a marked reduction in stem diameter, internodal length, leaf size, leaf lifespan and in flower and seed set.
- Full Text:
- Date Issued: 1982
An investigation into the taxonomy of the diatoms (Bacillariophyta) of the Sundays and Great Fish Rivers, with ecological observations on the Sundays River
- Archibald, Robert Eldred Mostert
- Authors: Archibald, Robert Eldred Mostert
- Date: 1982
- Subjects: Diatoms -- South Africa -- Eastern Cape Diatoms -- Classification Aquatic ecology -- South Africa -- Eastern Cape -- Sundays River
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4180 , http://hdl.handle.net/10962/d1003728
- Description: This report on the diatoms (Bacillariophyta) of the Sundays and Great Fish rivers is divided into two sections. In Volume 1 the taxonomy of the diatoms from these two river systems is examined. A total of 331 taxa were studied, of which 5 are described as new species. Two taxa are given new names, since they were previously known under later homonyms. Twenty seven taxa were recorded for the first time from South Africa, while a number of species are given amended descriptions in the light of fresh information obtained concerning them. A few taxa (chiefly South African forms) have been united with previously described taxa. For the remainder of the taxa mentioned in the text, comments are passed with regard to their taxonomy and dimensions, based on facts gained through literature surveys and personal observations of the relevant taxa. As far as possible all taxa examined in Volume 1 are illustrated, and these illustrations are presented in Volume 3 of this study. Volume 2 deals with the ecology of the diatoms in the Sundays River. Special emphasis is laid on relating the composition of the diatom associations at the selected stations to the ambient salinity and ionic composition of the water. A new index, the Salinity Tolerance Index (STI), is proposed to summarize by means of a numerical value the information obtained from the analysis of a diatom association with respect to the character of the component taxa, and to indicate whether the association is derived from a freshwater, brackish water or marine source. The efficacy of the STI is evaluated in the text. The effect of the geological formations of the Sundays River valley and the underground waters emanating from them is discussed in the text. The consequences of a severe drought in the lower Sundays River, including hypersaline water in the upper estuary, on the diatom flora are also investigated.
- Full Text:
- Date Issued: 1982
- Authors: Archibald, Robert Eldred Mostert
- Date: 1982
- Subjects: Diatoms -- South Africa -- Eastern Cape Diatoms -- Classification Aquatic ecology -- South Africa -- Eastern Cape -- Sundays River
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4180 , http://hdl.handle.net/10962/d1003728
- Description: This report on the diatoms (Bacillariophyta) of the Sundays and Great Fish rivers is divided into two sections. In Volume 1 the taxonomy of the diatoms from these two river systems is examined. A total of 331 taxa were studied, of which 5 are described as new species. Two taxa are given new names, since they were previously known under later homonyms. Twenty seven taxa were recorded for the first time from South Africa, while a number of species are given amended descriptions in the light of fresh information obtained concerning them. A few taxa (chiefly South African forms) have been united with previously described taxa. For the remainder of the taxa mentioned in the text, comments are passed with regard to their taxonomy and dimensions, based on facts gained through literature surveys and personal observations of the relevant taxa. As far as possible all taxa examined in Volume 1 are illustrated, and these illustrations are presented in Volume 3 of this study. Volume 2 deals with the ecology of the diatoms in the Sundays River. Special emphasis is laid on relating the composition of the diatom associations at the selected stations to the ambient salinity and ionic composition of the water. A new index, the Salinity Tolerance Index (STI), is proposed to summarize by means of a numerical value the information obtained from the analysis of a diatom association with respect to the character of the component taxa, and to indicate whether the association is derived from a freshwater, brackish water or marine source. The efficacy of the STI is evaluated in the text. The effect of the geological formations of the Sundays River valley and the underground waters emanating from them is discussed in the text. The consequences of a severe drought in the lower Sundays River, including hypersaline water in the upper estuary, on the diatom flora are also investigated.
- Full Text:
- Date Issued: 1982
Evaluation of Tucumania Tapiacola Dyar (Lepidoptera: Phycitidae) for biological control of jointed cactus in South Africa
- Authors: Hoffmann, John Hugh
- Date: 1982
- Subjects: Phycitidae Cactus -- South Africa Weeds -- Biological control -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5634 , http://hdl.handle.net/10962/d1005316
- Description: Jointed cactus, 0puntia aurantiaca Lindley, remains a problem and continues to expand its range in South Africa, in spite of a mandatory herbicidal control. programme. The feasibility of biologically controlling the weed is being explored because the cost of herbicides has escalated and, if it succeeds, biological control is permanent self perpetuating and relatively cheap. This thesis describes the introduction and release in South Africa of the phycitid moth, Tucumania tapiacola Dyar, as a potential biocontrol agent against jointed cactus. A preliminary objective of the study was to resolve the taxonomic confusion within the genus Tucumania, so that the various populations of the moth from widespread localities and from different host plants could be identified. The efficiency of mass-producing T. tapiacola in the insectary was continually improved through investigations of the insects biology, and its response to various environmental parameters. Techniques were developed to manipulate the different life-stages of T. tapiacola so that every release was made with the maximum possible number of individuals, all in the same stage of development. Trials were made with various methods for transporting and releasing T. tapiacola in the field, and the most successful of these were employed during the establishment programme. In all, approximately 830 000 T. tapiacola eggs, larvae and adults have been released at seven localities in South Africa, between May 1977 and February 1982. So far, the moth has failed to establish for more than three to five generations at any release site, for reasons that were not immediately apparent. The mortality factors acting against the immature stages of T. tapiacola have been investigated and quantified. The accumulated data were used to construct partial-life-tables and survivorship curves. These show that survival of the eggs, larvae and pupae differed in shaded and exposed habitats, and on small, medium and large O. aurantiaca plants. The overall mortality suffered by the immature stages alone did not account for the establishment failure. Alternatively, genetic problems that are commonly associated with the collection, mass production and release of biocontrol agents may have been responsible for the failure. Methods of overcoming these problems during future releases are discussed.
- Full Text:
- Date Issued: 1982
- Authors: Hoffmann, John Hugh
- Date: 1982
- Subjects: Phycitidae Cactus -- South Africa Weeds -- Biological control -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5634 , http://hdl.handle.net/10962/d1005316
- Description: Jointed cactus, 0puntia aurantiaca Lindley, remains a problem and continues to expand its range in South Africa, in spite of a mandatory herbicidal control. programme. The feasibility of biologically controlling the weed is being explored because the cost of herbicides has escalated and, if it succeeds, biological control is permanent self perpetuating and relatively cheap. This thesis describes the introduction and release in South Africa of the phycitid moth, Tucumania tapiacola Dyar, as a potential biocontrol agent against jointed cactus. A preliminary objective of the study was to resolve the taxonomic confusion within the genus Tucumania, so that the various populations of the moth from widespread localities and from different host plants could be identified. The efficiency of mass-producing T. tapiacola in the insectary was continually improved through investigations of the insects biology, and its response to various environmental parameters. Techniques were developed to manipulate the different life-stages of T. tapiacola so that every release was made with the maximum possible number of individuals, all in the same stage of development. Trials were made with various methods for transporting and releasing T. tapiacola in the field, and the most successful of these were employed during the establishment programme. In all, approximately 830 000 T. tapiacola eggs, larvae and adults have been released at seven localities in South Africa, between May 1977 and February 1982. So far, the moth has failed to establish for more than three to five generations at any release site, for reasons that were not immediately apparent. The mortality factors acting against the immature stages of T. tapiacola have been investigated and quantified. The accumulated data were used to construct partial-life-tables and survivorship curves. These show that survival of the eggs, larvae and pupae differed in shaded and exposed habitats, and on small, medium and large O. aurantiaca plants. The overall mortality suffered by the immature stages alone did not account for the establishment failure. Alternatively, genetic problems that are commonly associated with the collection, mass production and release of biocontrol agents may have been responsible for the failure. Methods of overcoming these problems during future releases are discussed.
- Full Text:
- Date Issued: 1982
Investigations into the ecology of a population of Citrus Red Scale (Aonidiella aurantii Mask.) in the Swaziland lowlands
- Authors: Atkinson, P R
- Date: 1982
- Subjects: Citrus -- Diseases and pests -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5619 , http://hdl.handle.net/10962/d1003733
- Description: In the Swaziland lowlands, biological control of the citrus pest red scale, Aonidiella aurantii (Mask), has been consistently unsuccessful although it is successful in middle altitude regions. However, recent cases of resistance to organophosphate insecticides elsewhere in southern Africa, make it important to reconsider biological control of red scale in the lowlands. Should similar resistance be evolved in this region, the pest could be controlled only by natural means together with oils. This account attempts to answer questions about the natural control of a red scale population in the lowlands, by examining data collected between 1972 and 1975. The population was continuously breeding with overlapped generations. It consisted of three sections, on leaves, twigs and fruit, having different rates of reproduction, development and mortality. These sections are considered separately but that on leaves, being relatively unimportant, is largely ignored. The generation mortality is estimated in the sections on twigs and fruit and related to climatic and biotic indices. The causes of seasonal and between-years variation in the sections on twigs and fruit are elucidated. The effectiveness of each kind of natural enemy is examined and the factors affecting natural enemy numbers are investigated. The question of population regulation is discussed. Differences in mean infestation levels in middle altitude and lowland regions are explained in terms of different rates of reproduction and mortality.
- Full Text:
- Date Issued: 1982
- Authors: Atkinson, P R
- Date: 1982
- Subjects: Citrus -- Diseases and pests -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5619 , http://hdl.handle.net/10962/d1003733
- Description: In the Swaziland lowlands, biological control of the citrus pest red scale, Aonidiella aurantii (Mask), has been consistently unsuccessful although it is successful in middle altitude regions. However, recent cases of resistance to organophosphate insecticides elsewhere in southern Africa, make it important to reconsider biological control of red scale in the lowlands. Should similar resistance be evolved in this region, the pest could be controlled only by natural means together with oils. This account attempts to answer questions about the natural control of a red scale population in the lowlands, by examining data collected between 1972 and 1975. The population was continuously breeding with overlapped generations. It consisted of three sections, on leaves, twigs and fruit, having different rates of reproduction, development and mortality. These sections are considered separately but that on leaves, being relatively unimportant, is largely ignored. The generation mortality is estimated in the sections on twigs and fruit and related to climatic and biotic indices. The causes of seasonal and between-years variation in the sections on twigs and fruit are elucidated. The effectiveness of each kind of natural enemy is examined and the factors affecting natural enemy numbers are investigated. The question of population regulation is discussed. Differences in mean infestation levels in middle altitude and lowland regions are explained in terms of different rates of reproduction and mortality.
- Full Text:
- Date Issued: 1982
Issues in Zulu relativization
- Authors: Poulos, George
- Date: 1982
- Subjects: Zulu language -- Relative clauses
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3618 , http://hdl.handle.net/10962/d1006939
- Description: Zulu is a language of the Nguni group of the South-Eastern Zone of Bantu languages and is spoken by approximately 5 400 000 people. As far back as 1848, the Zulu language was investigated by a missionary of the American Board in Natal, James C. Bryant. In that year his ideas on the language were put on paper under the title, The Zulu Language, and this valuable contribution of some 13 pages was published in the following year in the Journal of the Oriental Society . Bryant's work heralded the beginning of a tradition of analysis in Zulu that was to capture the interest of a number of investigators over a period stretching up until the present day.
- Full Text:
- Date Issued: 1982
- Authors: Poulos, George
- Date: 1982
- Subjects: Zulu language -- Relative clauses
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3618 , http://hdl.handle.net/10962/d1006939
- Description: Zulu is a language of the Nguni group of the South-Eastern Zone of Bantu languages and is spoken by approximately 5 400 000 people. As far back as 1848, the Zulu language was investigated by a missionary of the American Board in Natal, James C. Bryant. In that year his ideas on the language were put on paper under the title, The Zulu Language, and this valuable contribution of some 13 pages was published in the following year in the Journal of the Oriental Society . Bryant's work heralded the beginning of a tradition of analysis in Zulu that was to capture the interest of a number of investigators over a period stretching up until the present day.
- Full Text:
- Date Issued: 1982
Nathaniel James Merriman, Archdeacon and Bishop 1849-1882 : a study in church life and government
- Authors: Goedhals, Mary Mandeville
- Date: 1982
- Subjects: Merriman, Nathaniel James, 1809-1881
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2590 , http://hdl.handle.net/10962/d1007194
- Full Text:
- Date Issued: 1982
- Authors: Goedhals, Mary Mandeville
- Date: 1982
- Subjects: Merriman, Nathaniel James, 1809-1881
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2590 , http://hdl.handle.net/10962/d1007194
- Full Text:
- Date Issued: 1982
Nepticulidae (Lepidoptera) : a revised classification, and descriptions of some new taxa particularly from southern Africa
- Authors: Scoble, M J
- Date: 1982
- Subjects: Nepticulidae Nepticulidae--Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5801 , http://hdl.handle.net/10962/d1006183
- Description: Previous classifications of the Nepticulidae were based on species from the northern hemisphere, primarily western Europe (including the United Kingdom) and North America. The revised classification presented in the present work was developed from a study of material primarily from southern Africa, but also from Australia, Europe, North America, and the Orient. Most of the descriptive section deals with the taxonomy of the Nepticulidae of southern Africa. Nevertheless, a guide to the supraspecific classification of the family was a major aim. Cladistic methods were used to assess genealogy as far as possible. The degree to which it has been elucidated is incorporated into the classification. As a result of the study, the Nepticulidae are divided into two subfamilies. One of these subfamilies is divided into two tribes. Fifteen genera and six subgenera are recognised. Two keys are presented, one to subfamilies and tribes and the other to genera and subgenera. The species from southern Africa are included in eight genera, three of which are new. One hundred and seventeen species from southern Africa are considered. Seventy- two new species are described in this work. Of these 40 have been published and 32 appear as manuscript names. For some species described by previous workers lectotypes have been designated where appropriate. The primary types of all the known species from southern Africa have been examined. Observations on adult structure are discussed from the viewpoint of phylogenetic relationships both within the Nepticulidae and between the family and other lepidopteran groups. This has led to a re-interpretation and expansion of some aspects of nepticulid morphology. Numerical phenetic methods, which include cluster analyses and an ordination technique (principal component analysis), were used to check my personal assessment of phena. The illustrations (phenograms and ordination diagrams) provide a visual summary of phenetic relationships of as wide a range of Nepticulidae as possible. Aspects of the nature of taxonomic characters, ancestor-descendant relationships, and homoplasy are discussed. Brief comments are made on distribution, and host-plant choice and phylogeny.
- Full Text:
- Date Issued: 1982
- Authors: Scoble, M J
- Date: 1982
- Subjects: Nepticulidae Nepticulidae--Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5801 , http://hdl.handle.net/10962/d1006183
- Description: Previous classifications of the Nepticulidae were based on species from the northern hemisphere, primarily western Europe (including the United Kingdom) and North America. The revised classification presented in the present work was developed from a study of material primarily from southern Africa, but also from Australia, Europe, North America, and the Orient. Most of the descriptive section deals with the taxonomy of the Nepticulidae of southern Africa. Nevertheless, a guide to the supraspecific classification of the family was a major aim. Cladistic methods were used to assess genealogy as far as possible. The degree to which it has been elucidated is incorporated into the classification. As a result of the study, the Nepticulidae are divided into two subfamilies. One of these subfamilies is divided into two tribes. Fifteen genera and six subgenera are recognised. Two keys are presented, one to subfamilies and tribes and the other to genera and subgenera. The species from southern Africa are included in eight genera, three of which are new. One hundred and seventeen species from southern Africa are considered. Seventy- two new species are described in this work. Of these 40 have been published and 32 appear as manuscript names. For some species described by previous workers lectotypes have been designated where appropriate. The primary types of all the known species from southern Africa have been examined. Observations on adult structure are discussed from the viewpoint of phylogenetic relationships both within the Nepticulidae and between the family and other lepidopteran groups. This has led to a re-interpretation and expansion of some aspects of nepticulid morphology. Numerical phenetic methods, which include cluster analyses and an ordination technique (principal component analysis), were used to check my personal assessment of phena. The illustrations (phenograms and ordination diagrams) provide a visual summary of phenetic relationships of as wide a range of Nepticulidae as possible. Aspects of the nature of taxonomic characters, ancestor-descendant relationships, and homoplasy are discussed. Brief comments are made on distribution, and host-plant choice and phylogeny.
- Full Text:
- Date Issued: 1982
Perspectives on the nine symphonies of Anton Bruckner : aspects of thematic and harmonic compositional techniques, with special reference to the first and final movements, symphonies one to nine
- Authors: Gibson, Penelope Anne
- Date: 1982
- Subjects: Bruckner, Anton, 1824-1896 -- Symphonies
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2671 , http://hdl.handle.net/10962/d1007168
- Description: Preface: This thesis presents perspectives on Bruckner's compositional approach with regard to theme and harmony in the first and final movements of his symphonies one to nine. It must be realised that a fully systematic and comprehensive discussion along these lines would run into volumes. So, salient examples and common tendencies have been extracted as representative of the overall approach. However, Bruckner being the composer he is, is not dogmatic in his approach to composition and so the reader must at all times see for himself how the general technique is adapted to the individual usage in those parts not referred to in this thesis. The thesis presents the subject features of the expositions, first movements, as these are found in various adaptations in all other movements: it also aims to present a comparative study of the structural tonal principles of the works, showing how these influence the thematic forms. Whenever necessary, in the text, definitions are repeated in their original format to avoid cumbersome cross references. The most immediate source is the scores themselves, issued by the International Bruckner Society of Vienna, compiled by Dr. Leopold Nowak. All the analysis is based on these editions except for the third symphony which is based on the 2. Edition of 1878 (Wiesbaden G.M.B .H.)
- Full Text:
- Date Issued: 1982
- Authors: Gibson, Penelope Anne
- Date: 1982
- Subjects: Bruckner, Anton, 1824-1896 -- Symphonies
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2671 , http://hdl.handle.net/10962/d1007168
- Description: Preface: This thesis presents perspectives on Bruckner's compositional approach with regard to theme and harmony in the first and final movements of his symphonies one to nine. It must be realised that a fully systematic and comprehensive discussion along these lines would run into volumes. So, salient examples and common tendencies have been extracted as representative of the overall approach. However, Bruckner being the composer he is, is not dogmatic in his approach to composition and so the reader must at all times see for himself how the general technique is adapted to the individual usage in those parts not referred to in this thesis. The thesis presents the subject features of the expositions, first movements, as these are found in various adaptations in all other movements: it also aims to present a comparative study of the structural tonal principles of the works, showing how these influence the thematic forms. Whenever necessary, in the text, definitions are repeated in their original format to avoid cumbersome cross references. The most immediate source is the scores themselves, issued by the International Bruckner Society of Vienna, compiled by Dr. Leopold Nowak. All the analysis is based on these editions except for the third symphony which is based on the 2. Edition of 1878 (Wiesbaden G.M.B .H.)
- Full Text:
- Date Issued: 1982
Synthesis and reactions of sugar chlorosulphates
- Authors: Glass, Beverley Dawn
- Date: 1982
- Subjects: Chemical reactions Sugar -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3826 , http://hdl.handle.net/10962/d1006145
- Description: Summary: Partially chlorosulphated derivatives were synthesised for the purpose of examining the reactions of the chlorosulphonyloxy group in the presence of free hydroxyl groups. The behaviour of the chlorosulphonyloxy group was investigated under acidic conditions. Since sterically favoured chlorosulphonyloxy groups undergo facile replacement by chlorine to form chlorodeoxy sugars, some compounds possessing chlorosulphonyloxy groups which,due to polar and steric effects are not replaced by chloride,were investigated with a view to possible activation of the unfavourable centres towards nucleophilic substitution, thereby making available previously inaccessible chlorodeoxy sugars.
- Full Text:
- Date Issued: 1982
- Authors: Glass, Beverley Dawn
- Date: 1982
- Subjects: Chemical reactions Sugar -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3826 , http://hdl.handle.net/10962/d1006145
- Description: Summary: Partially chlorosulphated derivatives were synthesised for the purpose of examining the reactions of the chlorosulphonyloxy group in the presence of free hydroxyl groups. The behaviour of the chlorosulphonyloxy group was investigated under acidic conditions. Since sterically favoured chlorosulphonyloxy groups undergo facile replacement by chlorine to form chlorodeoxy sugars, some compounds possessing chlorosulphonyloxy groups which,due to polar and steric effects are not replaced by chloride,were investigated with a view to possible activation of the unfavourable centres towards nucleophilic substitution, thereby making available previously inaccessible chlorodeoxy sugars.
- Full Text:
- Date Issued: 1982
The development of cello technique in the string quartets of Joseph Haydn with special reference to (a) the various external influences causing this development and (b) the potential use of the cello parts within a teaching situation
- Sholto-Douglas, Ishbel Elizabeth Fraser
- Authors: Sholto-Douglas, Ishbel Elizabeth Fraser
- Date: 1982
- Subjects: Haydn, Joseph, 1732-1809 -- Quartets, strings Cello -- Methods Cello -- Instruction and study
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2666 , http://hdl.handle.net/10962/d1005864
- Description: From Introduction: In the middle of the eighteenth century, when Haydn began composing his first string quartets, violin writing was highly advanced and the violin an established solo instrument, its supremacy already firmly endorsed by the Italian Violin Schools of the seventeenth and early eighteenth centuries. The pace of development of the cello, however, was not comparable to that of the violin, despite the fact that the first cello known to us was made in 1572.
- Full Text:
- Date Issued: 1982
- Authors: Sholto-Douglas, Ishbel Elizabeth Fraser
- Date: 1982
- Subjects: Haydn, Joseph, 1732-1809 -- Quartets, strings Cello -- Methods Cello -- Instruction and study
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2666 , http://hdl.handle.net/10962/d1005864
- Description: From Introduction: In the middle of the eighteenth century, when Haydn began composing his first string quartets, violin writing was highly advanced and the violin an established solo instrument, its supremacy already firmly endorsed by the Italian Violin Schools of the seventeenth and early eighteenth centuries. The pace of development of the cello, however, was not comparable to that of the violin, despite the fact that the first cello known to us was made in 1572.
- Full Text:
- Date Issued: 1982
The ecology and control of Opuntia Aurantiaca in South Africa in relation to the cochineal insect, Dactylopius Austrinus
- Authors: Zimmermann, Helmuth G
- Date: 1982
- Subjects: Cochineal insect -- South Africa Cactus -- South Africa Weeds -- Control -- South Africa Insect-plant relationships
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5612 , http://hdl.handle.net/10962/d1003061
- Description: The cochineal insect Dactylopius austrinus De Lotto, which was released on jointed cactus, Opuntia aurantiaca Lindley, in South Africa in 1932, failed to bring the weed under an acceptable level of control in spite of the encouraging results during the first few years after release. The reasons for this apparent failure were never clearly understood. In 1957 the State embarked on an intensive herbicidal control programme which is still in force today. This sustained and expensive programme has undoubtedly reduced the density of the weed in most areas but has failed to solve the problem and the plant continues to expand its range. The biological control of o. aurantiaca in South Africa has been fundamentally influenced by this chemical control campaign. The relationship between chemical and biological control methods is reported in this study.
- Full Text:
- Date Issued: 1982
- Authors: Zimmermann, Helmuth G
- Date: 1982
- Subjects: Cochineal insect -- South Africa Cactus -- South Africa Weeds -- Control -- South Africa Insect-plant relationships
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5612 , http://hdl.handle.net/10962/d1003061
- Description: The cochineal insect Dactylopius austrinus De Lotto, which was released on jointed cactus, Opuntia aurantiaca Lindley, in South Africa in 1932, failed to bring the weed under an acceptable level of control in spite of the encouraging results during the first few years after release. The reasons for this apparent failure were never clearly understood. In 1957 the State embarked on an intensive herbicidal control programme which is still in force today. This sustained and expensive programme has undoubtedly reduced the density of the weed in most areas but has failed to solve the problem and the plant continues to expand its range. The biological control of o. aurantiaca in South Africa has been fundamentally influenced by this chemical control campaign. The relationship between chemical and biological control methods is reported in this study.
- Full Text:
- Date Issued: 1982
The Karoo caterpillar Loxostege Frustalis Zeller (Lepidoptera : Pyralidae) in relation to its host plants and natural enemies
- Authors: Möhr, Johann Diederich
- Date: 1982
- Subjects: Caterpillars -- South Africa Lepidoptera -- Host plants
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5604 , http://hdl.handle.net/10962/d1002054
- Description: The Karoo is an arid inland plateau in the central and northeastern Cape Province of South Africa and is characterised by sparse, stunted vegetation. The vegetation is rich in species, and over large areas species of Pentzia, which are drought-resistant shrubs, are extremely abundant. These plants are food for stock (mainly sheep), and because the larvae of the Karoo caterpillar periodically occur in sufficient numbers to defoliate the plants, they assume pest status. Fully-fed Loxostege frustalis larvae construct cases in the soil beneath their food plants and they overwinter in these cases. A census of the numbers of larval cases accumulated in the soil, conducted from 1975 to 1980, showed that an expanded distribution of the pentzias is responsible for the periodic larval outbreaks. Further, alternate food plants are an important food supply for L. frustalis larvae when they disperse under crowded conditions The census data for L. frustalis were analysed by constructing partial life tables for the life-history period from case construction to moth emergence. The mortality of 'encased larvae' is useful for assessing the impact of the known L. frustalis natural enemies. The most important natural enemies were the braconids Chelonus curvimaculatus Cameron, Macrocentrus maraisi Nixon and the fungus Beauveria bassiana (Balsamo) Vuillemin. The collective responses of all the natural enemies to the density of L. frustalis encased larvae was direct, but undercompensating, so that areas with more pentzias produced more L. frustais. Strategies for immediate measures to alleviate the Karoo caterpillar problem, and for future research, are discussed. It is concluded that reduction of pentzia populations to acceptable levels and/or supplementing pastures with non-host plants of L. frustalis offer the only practical solutions to the Karoo caterpillar problem. Biological control of L. frustalis is dismissed as an option for reducing the pest status of the Karoo caterpillar
- Full Text:
- Date Issued: 1982
- Authors: Möhr, Johann Diederich
- Date: 1982
- Subjects: Caterpillars -- South Africa Lepidoptera -- Host plants
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5604 , http://hdl.handle.net/10962/d1002054
- Description: The Karoo is an arid inland plateau in the central and northeastern Cape Province of South Africa and is characterised by sparse, stunted vegetation. The vegetation is rich in species, and over large areas species of Pentzia, which are drought-resistant shrubs, are extremely abundant. These plants are food for stock (mainly sheep), and because the larvae of the Karoo caterpillar periodically occur in sufficient numbers to defoliate the plants, they assume pest status. Fully-fed Loxostege frustalis larvae construct cases in the soil beneath their food plants and they overwinter in these cases. A census of the numbers of larval cases accumulated in the soil, conducted from 1975 to 1980, showed that an expanded distribution of the pentzias is responsible for the periodic larval outbreaks. Further, alternate food plants are an important food supply for L. frustalis larvae when they disperse under crowded conditions The census data for L. frustalis were analysed by constructing partial life tables for the life-history period from case construction to moth emergence. The mortality of 'encased larvae' is useful for assessing the impact of the known L. frustalis natural enemies. The most important natural enemies were the braconids Chelonus curvimaculatus Cameron, Macrocentrus maraisi Nixon and the fungus Beauveria bassiana (Balsamo) Vuillemin. The collective responses of all the natural enemies to the density of L. frustalis encased larvae was direct, but undercompensating, so that areas with more pentzias produced more L. frustais. Strategies for immediate measures to alleviate the Karoo caterpillar problem, and for future research, are discussed. It is concluded that reduction of pentzia populations to acceptable levels and/or supplementing pastures with non-host plants of L. frustalis offer the only practical solutions to the Karoo caterpillar problem. Biological control of L. frustalis is dismissed as an option for reducing the pest status of the Karoo caterpillar
- Full Text:
- Date Issued: 1982
Theories of economic underdevelopment: a general equilibrium analysis
- Authors: Black, Philip Andrew
- Date: 1982
- Subjects: Equilibrium (Economics) -- Mathematical models Economic development -- Mathematical models Developing countries -- Economic conditions -- Mathematical models
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1049 , http://hdl.handle.net/10962/d1006235
- Description: This thesis is mainly concerned with the question whether 'conventional' economic theory - especially the neoclassical theory of general equilibrium - is sufficiently flexible to accommodate the particular conditions prevailing in the developing countries. It is argued that most existing theories of economic underdevelopment adopt an interpretative approach which essentially amounts to relaxing some of the chief assumptions of the neoclassical theory. When applied to the two-sector model of general equilibrium, these theories generally yield predictions which are vastly different from those associated with the neoclassical assumptions of perfect competition, unlimited factor substitutability and unrestricted resource mobility. Several theories seek to explain the development problem in terms of the specific production processes used in poor countries. Myrdal's (1957) theory of cumulative causation, for example, effectively introduces increasing returns to scale in at least one sector or region of the economy; in contrast to the neoclassical theory, he thus nvisages a cumulative process of regional divergence in the output level per worker. Similarly, Richard Eckaus's (1955) explanation of the "factor-proportions problem" is based on the assumption of limited factor substitutability. This enables him to establish the existence of a so-called "unemployment equiIibrium", thus implying that developing countries may be faced with a conflict between the objective of maximizing social -welfare on the one hand, and that of full employment on the other. More recently, Leibenstein (1960) has shown that this trade-off may be complicated by the introduction of capital-biased technological inventions and innovations. The solution to the factor-proportions problem consists in the adoption of more appropriate, usually labour-biased technologies, increased capital formation and a reduction in the rate of population growth. Much of the postwar literature on economic development has focused on the imperfectly competitive structure of the product and the factor markets in developing countries. Myint (1954) has highlighted the role played by monopolies and ligopolies during the "opening-up" process of economic development. Likewise, both Lewis's (1954) dualist theory and Todaro's (1969; 1971) model of rural-urban migration attempt to explain the unemployment problem in terms of various factor price distortions. In an international context, Prebisch (1950; 1959) and Singer (1950) have again shown how prevailing differences in the structure of markets between developed and developing countries may turn the terms of trade against the latter; using a two-sector model, Bhagwati (1958) has demonstrated that such a deterioration in the terms of trade could bring about a net decrease in the welfare level of the countries concerned. Generally, the policy measures relevant to the "market imperfections" problem include the creation of job opportunities in the rural (rather than urban) sector, the encouragement of informal-sector enterprises,and the imposition of factor taxes and subsidies as a means of counteracting the adverse effect of factor price distortions on employment. A more recent approach to the unemployment problem is the plea by the International Labor Office (1970; 1972) for a redistribution of income within the developing countries. In terms of the two-sector model, such a policy may well succeed in eliminating labour unemployment caused by fixed factor proportions and/or factor price distortions. It should be realized, though, that a redistribution of income may lower the aggregate savings level, and hence also the growth rates of capital and labour employment in the economy. On the whole, it would seem that these theories do indeed adopt a modified version of the neoclassical theory in providing a fairly comprehensive explanation of the economic problems of labour unemployment, low incomes and inequality.
- Full Text:
- Date Issued: 1982
- Authors: Black, Philip Andrew
- Date: 1982
- Subjects: Equilibrium (Economics) -- Mathematical models Economic development -- Mathematical models Developing countries -- Economic conditions -- Mathematical models
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1049 , http://hdl.handle.net/10962/d1006235
- Description: This thesis is mainly concerned with the question whether 'conventional' economic theory - especially the neoclassical theory of general equilibrium - is sufficiently flexible to accommodate the particular conditions prevailing in the developing countries. It is argued that most existing theories of economic underdevelopment adopt an interpretative approach which essentially amounts to relaxing some of the chief assumptions of the neoclassical theory. When applied to the two-sector model of general equilibrium, these theories generally yield predictions which are vastly different from those associated with the neoclassical assumptions of perfect competition, unlimited factor substitutability and unrestricted resource mobility. Several theories seek to explain the development problem in terms of the specific production processes used in poor countries. Myrdal's (1957) theory of cumulative causation, for example, effectively introduces increasing returns to scale in at least one sector or region of the economy; in contrast to the neoclassical theory, he thus nvisages a cumulative process of regional divergence in the output level per worker. Similarly, Richard Eckaus's (1955) explanation of the "factor-proportions problem" is based on the assumption of limited factor substitutability. This enables him to establish the existence of a so-called "unemployment equiIibrium", thus implying that developing countries may be faced with a conflict between the objective of maximizing social -welfare on the one hand, and that of full employment on the other. More recently, Leibenstein (1960) has shown that this trade-off may be complicated by the introduction of capital-biased technological inventions and innovations. The solution to the factor-proportions problem consists in the adoption of more appropriate, usually labour-biased technologies, increased capital formation and a reduction in the rate of population growth. Much of the postwar literature on economic development has focused on the imperfectly competitive structure of the product and the factor markets in developing countries. Myint (1954) has highlighted the role played by monopolies and ligopolies during the "opening-up" process of economic development. Likewise, both Lewis's (1954) dualist theory and Todaro's (1969; 1971) model of rural-urban migration attempt to explain the unemployment problem in terms of various factor price distortions. In an international context, Prebisch (1950; 1959) and Singer (1950) have again shown how prevailing differences in the structure of markets between developed and developing countries may turn the terms of trade against the latter; using a two-sector model, Bhagwati (1958) has demonstrated that such a deterioration in the terms of trade could bring about a net decrease in the welfare level of the countries concerned. Generally, the policy measures relevant to the "market imperfections" problem include the creation of job opportunities in the rural (rather than urban) sector, the encouragement of informal-sector enterprises,and the imposition of factor taxes and subsidies as a means of counteracting the adverse effect of factor price distortions on employment. A more recent approach to the unemployment problem is the plea by the International Labor Office (1970; 1972) for a redistribution of income within the developing countries. In terms of the two-sector model, such a policy may well succeed in eliminating labour unemployment caused by fixed factor proportions and/or factor price distortions. It should be realized, though, that a redistribution of income may lower the aggregate savings level, and hence also the growth rates of capital and labour employment in the economy. On the whole, it would seem that these theories do indeed adopt a modified version of the neoclassical theory in providing a fairly comprehensive explanation of the economic problems of labour unemployment, low incomes and inequality.
- Full Text:
- Date Issued: 1982
Witwatersrand genesis: a comparative study of some early gold mining companies, 1886-1894
- Authors: Webb, Arthur (Arthur C M)
- Date: 1982
- Subjects: Gold mines and mining -- South Africa -- History Gold mines and mining -- South Africa -- Witwatersrand -- History Ferreira Gold Mining Company (Firm) Witwatersrand Gold Mining Company (Firm) Simmer and Jack Gold Mining Company (Firm) Wemmer Gold Mining Company (Firm)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1029 , http://hdl.handle.net/10962/d1003725
- Description: Preface: For anyone standing on the ridge of the Witwatersrand on a spring day in September 1886 the sight immediately to the south represented a hive of activity and hope. Nearly a hundred years later ample evidence stretches away on both sides of the watershed to confirm the fulfilment of those early sentiments. It is, nevertheless, all too easy to ignore the struggles and failures which marked the beginnings of the world's greatest gold field in the light of its subsequent abundant success. Only when attention is turned to the individual companies formed to exploit the discovery does the true picture emerge of the lack of adequate technological and managerial knowledge amongst the early pioneers and of the financial frailty of their companies. The object of this thesis is to shed light on these beginnings by reviewing the histories of four of the earliest companies established to work the main reef. The approach adopted is to scrutinize the material available with a view to determining the motivations and actions of the managements of the various companies with regard to their economic environment, whether within or without the individual company. Clearly, the availability of information is a major determinant of the success of any such venture and this was particularly so in the case of the companies considered. With the exception of the Barlow Rand Limited holding of the H. Eckstein and Company Archives, which offers an integral coverage of that firm's dealings with the emerging industry, and which is certainly the most comprehensive source of information available to the researcher, little material relating to specific gold mining companies has survived. Under these circumstances it was necessary to rely heavily for information on the local press. These newspapers proved an invaluable source in this regard. As a mining camp with a limited capacity for generating newsworthy incidents, the newspapers of early Johannesburg found an eager readership for information about the industry which lay at the heart of the community. For their part, the managements of the various mining companies found in the pages of the local press an outlet for intelligence both true and false; the press was a useful vehicle for the publication of directors' and annual reports to meet a wider audience, but similarly it could be and was used to disseminate 'spectacular' reports calculated to influence the status of a company's stock on the local share market. As a research source the press has thus to be approached with caution but its value, if the warning is heeded, is in no way diminished. Beyond these two sources the next most valuable accumulation of data on the early industry is "The Gold Fields Collection" housed in the Cory Library for Historical Research at Rhodes University. As a collection it is far from complete and it is to be hoped that the donors will in future see fit to augment it with further material as this becomes available. It neverthess proved an invaluable source for the investigation of at least one of the companies of the study and for a general background to the industry.
- Full Text:
- Date Issued: 1982
- Authors: Webb, Arthur (Arthur C M)
- Date: 1982
- Subjects: Gold mines and mining -- South Africa -- History Gold mines and mining -- South Africa -- Witwatersrand -- History Ferreira Gold Mining Company (Firm) Witwatersrand Gold Mining Company (Firm) Simmer and Jack Gold Mining Company (Firm) Wemmer Gold Mining Company (Firm)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1029 , http://hdl.handle.net/10962/d1003725
- Description: Preface: For anyone standing on the ridge of the Witwatersrand on a spring day in September 1886 the sight immediately to the south represented a hive of activity and hope. Nearly a hundred years later ample evidence stretches away on both sides of the watershed to confirm the fulfilment of those early sentiments. It is, nevertheless, all too easy to ignore the struggles and failures which marked the beginnings of the world's greatest gold field in the light of its subsequent abundant success. Only when attention is turned to the individual companies formed to exploit the discovery does the true picture emerge of the lack of adequate technological and managerial knowledge amongst the early pioneers and of the financial frailty of their companies. The object of this thesis is to shed light on these beginnings by reviewing the histories of four of the earliest companies established to work the main reef. The approach adopted is to scrutinize the material available with a view to determining the motivations and actions of the managements of the various companies with regard to their economic environment, whether within or without the individual company. Clearly, the availability of information is a major determinant of the success of any such venture and this was particularly so in the case of the companies considered. With the exception of the Barlow Rand Limited holding of the H. Eckstein and Company Archives, which offers an integral coverage of that firm's dealings with the emerging industry, and which is certainly the most comprehensive source of information available to the researcher, little material relating to specific gold mining companies has survived. Under these circumstances it was necessary to rely heavily for information on the local press. These newspapers proved an invaluable source in this regard. As a mining camp with a limited capacity for generating newsworthy incidents, the newspapers of early Johannesburg found an eager readership for information about the industry which lay at the heart of the community. For their part, the managements of the various mining companies found in the pages of the local press an outlet for intelligence both true and false; the press was a useful vehicle for the publication of directors' and annual reports to meet a wider audience, but similarly it could be and was used to disseminate 'spectacular' reports calculated to influence the status of a company's stock on the local share market. As a research source the press has thus to be approached with caution but its value, if the warning is heeded, is in no way diminished. Beyond these two sources the next most valuable accumulation of data on the early industry is "The Gold Fields Collection" housed in the Cory Library for Historical Research at Rhodes University. As a collection it is far from complete and it is to be hoped that the donors will in future see fit to augment it with further material as this becomes available. It neverthess proved an invaluable source for the investigation of at least one of the companies of the study and for a general background to the industry.
- Full Text:
- Date Issued: 1982
A victimological study among Coloureds in the Cape Peninsula
- Authors: Strijdom, Hendrik Gert
- Date: 1983
- Subjects: Victims of crimes -- South Africa -- Western Cape Colored people (South Africa) -- Social conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3342 , http://hdl.handle.net/10962/d1004582
- Description: From Introduction: Criminology developed as a reaction to the various revolutions that were occurring in the European countries during the eighteenth and nineteenth centuries. In response to the turmoil and disorder of Western society criminologists attempted to discover the natural laws of society hoping to establish a stable social order. Crime was regarded as something that disturbed society and, therefore, had to be controlled or prevented. According to Quinney and Wildeman (1977) the development of criminology can be viewed as an ongoing attempt to explain crime in terms of established social order. They state that in the history of criminology there is, however, a lack of a clear accumulative theoretical growth and continue as follows: "No line of theoretical development can be found that leads to a well-developed body of knowledge. The study of crime is characterized by a number of divergent theoretical perspectives that exist in relative isolation from one another" (p. 38). Quinney and Wildeman (1977) distinguish five theoretical perspectives in the development of criminology namely: (I) early and classical criminological thought, (2) nineteenth-century sociological criminology, (3) nineteenth-century biological criminology, (4) twentieth-century eclectic criminology, and (5) twentieth-century sociological criminology.
- Full Text:
- Date Issued: 1983
- Authors: Strijdom, Hendrik Gert
- Date: 1983
- Subjects: Victims of crimes -- South Africa -- Western Cape Colored people (South Africa) -- Social conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3342 , http://hdl.handle.net/10962/d1004582
- Description: From Introduction: Criminology developed as a reaction to the various revolutions that were occurring in the European countries during the eighteenth and nineteenth centuries. In response to the turmoil and disorder of Western society criminologists attempted to discover the natural laws of society hoping to establish a stable social order. Crime was regarded as something that disturbed society and, therefore, had to be controlled or prevented. According to Quinney and Wildeman (1977) the development of criminology can be viewed as an ongoing attempt to explain crime in terms of established social order. They state that in the history of criminology there is, however, a lack of a clear accumulative theoretical growth and continue as follows: "No line of theoretical development can be found that leads to a well-developed body of knowledge. The study of crime is characterized by a number of divergent theoretical perspectives that exist in relative isolation from one another" (p. 38). Quinney and Wildeman (1977) distinguish five theoretical perspectives in the development of criminology namely: (I) early and classical criminological thought, (2) nineteenth-century sociological criminology, (3) nineteenth-century biological criminology, (4) twentieth-century eclectic criminology, and (5) twentieth-century sociological criminology.
- Full Text:
- Date Issued: 1983
Aspects of prostacyclin in experimental hypertension
- Authors: Botha, Julia Hilary
- Date: 1983
- Subjects: Prostacyclin Prostaglandins Prostaglandin endoperoxides Thromboxanes Hypertension
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3825 , http://hdl.handle.net/10962/d1006109
- Description: A new prostaglandin - prostaglandin X (later renamed prostacyclin or prostaglandin I₂ (PGI₂)), was discovered by Moncada, Gryglewski, Bunting and Vane in 1976. This unstable substance was shown to be produced by vascular tissue and to be a vasodilator and the most potent endogenous inhibitor of platelet aggregation known. Because of its properties, it appeared that a lack of it may be related to the development and or maintenance of hypertension, a disorder featuring vasoconstriction and an increased tendency to arterial thrombosis. The present studies aimed to investigate this possibility using a rat model. A bioassay for prostacyclin was first perfected. This consisted of a modification of the method used by Moncada, Higgs and Vane (1977): PGI₂ released by rat aortic strips, during incubation in tris buffer, was measured by assessing the ability of the incubate to inhibit adenosine diphosphate induced aggregation of human platelets, as compared to the inhibitory effect of standard prostacyclin sodium salt. The specificity of the assay for the detection of PGI₂ was tested. The abil ity of hypertensive rat aorta to release prostacycl in was investigated in two studies. The first compared aortas of Wistar rats of the New Zealand genetically hypertensive strain (GH) with those of matched normotensive Wistar controls. In the second study, hypertension was induced by wrappi ng the ri ght kidney with surgical silk and removing the contralateral kidney. Ten weeks later, aortic generation of prostacyclin by these animals was compared with that of matched sham controls which had received identical surgical manipulation but for the application of silk to the right kidney. Contrary to expectation, in both forms of hypertension, aortas of the rats with elevated pressure produced consistently more prostacyclin than those of matched controls. In order to discover more about the relationship between elevated pressure and elevated PGI₂ production, the effect of pressure reduction with hypotensive agents on the ability of GH rat aortas to produce prostacyclin, was investigated. After pressure had been controlled within normal range for one week (achieved by oral administration of furosemide, dihydralazine and reserpine for one month), aortic PGI₂ was reduced in comparison with matched GH controls. However, the reduction was not consistent and statistical significance was not reached. Because it was subsequently reported by other workers, that some of the hypotensive agents which had been employed may effect prostaglandin levels per se, no conclusions could be drawn from this study as to any possible direct relationships between pressure and aortic prostacyclin generating capacity. A further means of reducing elevated pressure (which had no inherent effect on prostaglandin levels) was thus sought. A mechanical method was eventually selected, application of a silver clip to the aortas of GH rats, just below the diaphragm, producing an immediate reduction in pressure distal to the constriction. Eighteen hours with later, PGI₂ production by these distal aortas those of matched sham GH controls and was was compared found to be consistently reduced. These results indicate that the ability to produce PGI₂ may be influenced by prior local pressure changes and that the increased capacity of hypertensive rat aortas to generate prostacyclin may be related to the increased mechanical transmural stress consequent on elevated pressure. Since haemostatic balance must be influenced not only by vascular PGI₂ generation but also by platelet sensitivity to PGI₂, the response of GH platelets to the anti-aggregatory effect of prostacyc1in was also investigated. As it had been shown by Sinzinger, Si1berbauer, Horsch and Gall (1981) that intra-arterial infusion of PGI₂ in humans decreased platelet sensitivity to the substance, the possibility existed that platelet sensitivity in hypertension might be reduced. This hypothesis was, however, invalidated as the sensitivity of GH platelets to the anti-aggregatory effect of PGI₂ was almost identical to that of normotensive controls. The shortcomings of the methodology and the possible importance of these findings in the hypertensive animal are discussed. The idea that elevated PGI₂ in hypertension may play a protective role both with respect to platelet aggregation and in attenuating further pressure rises is considered. It is finally suggested that it will be possible to draw more accurate conclusions as to the meaning of the increased PGI₂ generation in hypertension (both in relation to vascular tone and platelet function) only when details of production of, and sensitivity to, thromboxane A₂ are known. Thromboxane A₂ (TXA₂) is a vasoconstrictor and promotor of aggregation (Hamberg, Svensson and Samuelson, 1975) and it may be that, despite elevated vascular PGI₂ generation, the TXA₂/PGI₂ balance is still tipped in favour of vasoconstriction and platelet aggregation in hypertension.
- Full Text:
- Date Issued: 1983
- Authors: Botha, Julia Hilary
- Date: 1983
- Subjects: Prostacyclin Prostaglandins Prostaglandin endoperoxides Thromboxanes Hypertension
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3825 , http://hdl.handle.net/10962/d1006109
- Description: A new prostaglandin - prostaglandin X (later renamed prostacyclin or prostaglandin I₂ (PGI₂)), was discovered by Moncada, Gryglewski, Bunting and Vane in 1976. This unstable substance was shown to be produced by vascular tissue and to be a vasodilator and the most potent endogenous inhibitor of platelet aggregation known. Because of its properties, it appeared that a lack of it may be related to the development and or maintenance of hypertension, a disorder featuring vasoconstriction and an increased tendency to arterial thrombosis. The present studies aimed to investigate this possibility using a rat model. A bioassay for prostacyclin was first perfected. This consisted of a modification of the method used by Moncada, Higgs and Vane (1977): PGI₂ released by rat aortic strips, during incubation in tris buffer, was measured by assessing the ability of the incubate to inhibit adenosine diphosphate induced aggregation of human platelets, as compared to the inhibitory effect of standard prostacyclin sodium salt. The specificity of the assay for the detection of PGI₂ was tested. The abil ity of hypertensive rat aorta to release prostacycl in was investigated in two studies. The first compared aortas of Wistar rats of the New Zealand genetically hypertensive strain (GH) with those of matched normotensive Wistar controls. In the second study, hypertension was induced by wrappi ng the ri ght kidney with surgical silk and removing the contralateral kidney. Ten weeks later, aortic generation of prostacyclin by these animals was compared with that of matched sham controls which had received identical surgical manipulation but for the application of silk to the right kidney. Contrary to expectation, in both forms of hypertension, aortas of the rats with elevated pressure produced consistently more prostacyclin than those of matched controls. In order to discover more about the relationship between elevated pressure and elevated PGI₂ production, the effect of pressure reduction with hypotensive agents on the ability of GH rat aortas to produce prostacyclin, was investigated. After pressure had been controlled within normal range for one week (achieved by oral administration of furosemide, dihydralazine and reserpine for one month), aortic PGI₂ was reduced in comparison with matched GH controls. However, the reduction was not consistent and statistical significance was not reached. Because it was subsequently reported by other workers, that some of the hypotensive agents which had been employed may effect prostaglandin levels per se, no conclusions could be drawn from this study as to any possible direct relationships between pressure and aortic prostacyclin generating capacity. A further means of reducing elevated pressure (which had no inherent effect on prostaglandin levels) was thus sought. A mechanical method was eventually selected, application of a silver clip to the aortas of GH rats, just below the diaphragm, producing an immediate reduction in pressure distal to the constriction. Eighteen hours with later, PGI₂ production by these distal aortas those of matched sham GH controls and was was compared found to be consistently reduced. These results indicate that the ability to produce PGI₂ may be influenced by prior local pressure changes and that the increased capacity of hypertensive rat aortas to generate prostacyclin may be related to the increased mechanical transmural stress consequent on elevated pressure. Since haemostatic balance must be influenced not only by vascular PGI₂ generation but also by platelet sensitivity to PGI₂, the response of GH platelets to the anti-aggregatory effect of prostacyc1in was also investigated. As it had been shown by Sinzinger, Si1berbauer, Horsch and Gall (1981) that intra-arterial infusion of PGI₂ in humans decreased platelet sensitivity to the substance, the possibility existed that platelet sensitivity in hypertension might be reduced. This hypothesis was, however, invalidated as the sensitivity of GH platelets to the anti-aggregatory effect of PGI₂ was almost identical to that of normotensive controls. The shortcomings of the methodology and the possible importance of these findings in the hypertensive animal are discussed. The idea that elevated PGI₂ in hypertension may play a protective role both with respect to platelet aggregation and in attenuating further pressure rises is considered. It is finally suggested that it will be possible to draw more accurate conclusions as to the meaning of the increased PGI₂ generation in hypertension (both in relation to vascular tone and platelet function) only when details of production of, and sensitivity to, thromboxane A₂ are known. Thromboxane A₂ (TXA₂) is a vasoconstrictor and promotor of aggregation (Hamberg, Svensson and Samuelson, 1975) and it may be that, despite elevated vascular PGI₂ generation, the TXA₂/PGI₂ balance is still tipped in favour of vasoconstriction and platelet aggregation in hypertension.
- Full Text:
- Date Issued: 1983