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The effects of environmental water hardness and alkalinity on the giant freshwater prawn Macrobrachium rosenbergii (de Man) were investigated. Preliminary studies indicated significant interaction effects between alkalinity and hardness and also that the ratio of calcium to magnesium ions in the water was important for growth. At moderate alkalinity a Ca:Mg ratio of 1:1 allowed better growth than ratios of 4:1 and 1:4. In a series of experiments made with postlarval and juvenile prawns, the levels of alkalinity and hardness in the test waters were adjusted separately so that the influence of each factor could be determined independently as well as in combination. Data on aspects of survival, growth and carapace mineralization were recorded. The results showed that, in contrast to some reports, high water hardness did not necessarily constrain performance provided alkalinity was low (2Smg 1' as CaCOs). On the other hand, high alkalinity (>100mg 1') caused a number of problems. These included increased mortalities (particularly when hardness was low. 20mg 1'), an increased incidence of a pathological condition called "white muscle syndrome" , a reduced size increment achieved at moult while, paradoxically, increasing the moulting frequency, and an enhanced calcium deposition in carapaces during intermoult. In all experiments, postlarvae were more sensitive than juveniles to adverse combinations of alkalinity and hardness. This feature is discussed in relation to Asian prawn farming practises. The activity of dephosphorylating enzymes in gills from immediate postmoult and from intermoult prawns exposed to low and high alkalinity was measured. The activity was maximal at both low and high alkalinity in postmoult prawns i.e. during the time of expected maximum calcium uptake, and significantly lower in intermoult prawns but only when alkalinity was low. At high alkalinity, activity in intermoult prawns remained at postmoult levels suggesting that this activity was associated with the increased calcium deposition observed in intact animals held in high alkalinity waters.

Cholera in one of the most important health problems of many areas of Asia. Despite extensive research, workers are still confronted with a number of unsolved problems that stand in the way of control and ultimate eradication of the disease. The immediate problems presented by cholera at this time are related to its treatment and its practical control. The clinical and biochemical abnormalities that occur in the cholera patient can be rapidly and consistently corrected by intravenous administration of fluids approximately equal in volume and electrolyte concentration to the fluids lost via the gastrointestinal route. Although treatment by rehydration is good, specific treatment must wait until we know more regarding the mechanism of pathogenicity in cholera. Alternatively, it may be that phage therapy still is worthy of consideration but this is doubtful. The control of cholera depends on several factors. (i) Improvement of sanitation, provision of safe water, satisfactory disposal of excreta and health education of the public to improve personal hygiene are essentials. (ii) Further investigation of the epidemiology of cholera and cholera like diseases will assist control. This demands more research into cholera phages and genetic mechanisms so that epidemics can be traced and understood. (iii) Finally, active immunization may achieve control of cholera, but we meanwhile require more knowledge of mechanisms of pathogenicity so that good protective antigens may be prepared. The writer has therefore investigated the 2 obviously important aspects of (A) The toxins of cholera; (B) The phage, and genetics related to cholera. These studies are reported in Sections I and II of this thesis respectively.

Correction and adjustment of observed angles and sides in geodetic networks are necessary for the purpose of the correct location of coordinated points. Correction equations are usually in the form of linear overdetermined (observation) or underdetermined (condition) equations which are solved by the least squares theorem. The introduction of the electro-magnetic methods of linear measurement requires the adjustment of sides as well as the adjustment of angles necessary in classical triangulation nets. For the simultaneous adjustment of angles and sides two new sets of conditions have been introduced: (i) the area misfit condition, where the area obtained from distances and angles has to satisfy a special condition, and (ii) that the sum of the projections of the three sides of a triangle on the coordinate axes have to satisfy a zero condition. A special study has been made into the adjustment of the braced geodetic quadrilateral, as being one of the most favourable figures from the adjustment point of view. The different apices of this quadrilateral have been investigated to allow a choice to be made as to which of them shall be introduced in an angle misfit condition during adjustment. This gives rise to the conclusion that all apices will introduce the same corrections for all practical purposes. Since observed angles and sides are different physical quantities, the question of relative weighting has been given special attention and recommendations have been made in the light of various theoretical and practical investigations. The Systematic relaxation method for adjusting survey nets has been theoretically derived by Professors Southwell and Black based on the minimum strain-energy conserved in an elastic frame-work at the position of equilibrium. Using this theory mechanical analogues have been designed and constructed for the first time to carry out the adjustment of the triangulation net directly from field observations, without the necessity of forming and solving a set of linear equations. An analogue for the adjustment of angles was found to be excessively complicated mechanically and difficult to use in practice. Through the use of a direction adjustment method these limitations have been overcome. The final model constructed achieved comparable results to those obtained numerically by a least squares solution. Suggestions for a more highly developed version are made and the situations favourable to mechanical analogue computations are discussed. The use of an electrical analogue as suggested by Su using a D.C. circuit has been thoroughly investigated from both the theoretical and practical points of view, which showed that such a solution will be simple only for certain limited cases. As an alternative the possibilities of the more general purpose electronic analogue computer have been investigated via the solution of correction equations. Various examples have been solved on this computer which proved to have several advantages over other computation methods. Finally equivalent problems have been solved numerically on a digital computer for a comparison of the relative merits of analogue and digital methods for the particular case of adjustment of geodetic networks. The relative merits of these solutions are discussed in the light of different problems and circumstances.