The Value of Well-Designed Experiments in Studying Diseases with Special Reference to Amphibians

Relatively few studies of amphibian diseases have employed standard ecological experimental designs. We discuss what constitutes a well-designed ecological experiment and encourage their use in disease studies. We illustrate how well-designed experiments can be used to determine the effects of pathogens on amphibians and we illustrate how ancillary information, including that collected using molecular tools, can be used to enhance the value of such experiments.     

Discriminant Value of Thyroid Function Tests

Different thyroid function tests permitted a final classification of 204 consecutive patients with suspected thyroid disorders into three populations (thyrotoxic, euthyroid, and hypothyroid). Linear discriminant analysis was applied to all test results (10 variates) on adjacent population pairs. Two invitro tests (serum protein bound iodine (P.B.I.) and tri-iodothyronine (T-3) uptake values) gave good separation of thyrotoxic from euthyroid patients and fairly good distinction of hypothyroid patients. If a ¹³¹I uptake figure was then added to the in-vitro results most patients (95·5%), including thse initially classified as equivocal, were correctly diagnosed. Other tests, including clinical questionnaires, were poor discriminants.Two new techniques of utilizing the test data were devised. Firstly, the data from the two in-vitro tests were also displayed graphically, and oblique boundary lines derived from the discriminant functions gave better separation of patients than previously used limits or mathematical expressions of “free thyroxine.” Secondly, a nomogram incorporating the best four discriminants was designed as a diagnostic aid and proved to be the best means of interpreting the tests.Discriminant analysis of this kind can be used in the interpretation of diagnostic tests in any branch of medicine, and it allows the best use to be made of the available data.     

An Acrylamide Gel Electrophoretic Study of the Seed Proteins of Brassica and Sinapis Species, with Special Reference to their Taxonomic Value

The albumin and globulin fractions of the seeds of a wide rangeof Brassica and Sinapis species have been investigated by acrylamidegel electrophoresis. The results of this investigation havebeen presented in the form of a three-dimensional model andcorrelation between this model, the distribution of the proteins,and the established taxonomy has been indicated.     

Seed Nutrient Reserves of Proteaceae with Special Reference to Protein Bodies and their Inclusions

The storage reserves of seeds of a wide taxonomic range of Proteaceaewere examined by chemical analyses for macronutrients, proteinand non-protein-N composition, by light microscopy of cotyledonarytissue for morphological and histochemical study of proteinbodies and their inclusions, and by X-ray point microanalysisfor determining the elemental composition of the various typesof inclusions. The 70 species from 30 genera showed higher levelsof N, P and Mg but not of Ca and K in seed dry matter in comparisonwith a similarly sized sample of non-proteaceous species. Small-seededProteaceae tended to have seed dry matter significantly moreenriched with minerals than large-seeded species. Protein levelsranged from 18 to 89 per cent of embryo dry weight (mean for32 species 39.5 per cent). Protein and ethanol soluble N fractionsof many species were exceptionally rich in arginine. Oil wasabundant in most species, starch universally absent. Seven typesof protein body inclusions were identified on the basis of size,shape and reaction to toluidine blue. Mineral composition ofthe inclusions differed significantly, particularly in ratiosof Ca to P and of P to S and Mg. All genera and certain speciescould be distinguished one from another on the basis of distributionand frequency of inclusion types within tissues of the cotyledonsand staining patterns of protein bodies to amido black. Thetaxonomic significance of the data is evaluated. Seed reserves, Proteaceae, protein bodies, protein body inclusions, mineral composition, taxonomy     

Some Aspects of Olfaction in Fishes, with Special Reference to Orientation

Olfactory cues play an important role in the behavior of fishes,such as the procurement of food, recognition of sex, defenseagainst predators, parental behavior, and orientation. By monitoringand three-dimensional photographic techniques, analyses weremade of some aspects of orientation mechanisms through olfaction.None of the marine and freshwater species investigated movedrandomly in an experimental environment void of directionalcues. When changing direction, the radius of the curve is fixedwithin fairly narrow limits and seems to be species-specific.Left and right-hand turns are not evenly distributed. This locomotorbehavior results in a non-random pattern of relatively rigidparameters. The introduction of an odor without directionalcues causes these parameters to change drastically. Invariably,the radius of the curve in changing direction decreases andthe ratio of left-handed to right-handed turns is greatly changedin most experiments. When an attractant odor is introduced uni-directionally,none of the species studied could locate the source, unlessthe odor was associated with a differential in the rate of flowof the water. It is suggested that an attractant odor releasesrheotactic response, which was not present in the animal inthe experiments previously referred to, so that the localizationof the source of the odor takes place through rheotaxis ratherthan through orienting cues provided by the odor gradient. Furthermore,it is proposed that this mechanism forms the basis for homingorientation in those migrating species in which olfactory cuesare required for the localization of spawning grounds in riversystems.     

Chemotaxis of Fungal Zoospores,with Special Reference to Aphanomyces cochlioides

Zoospores of phytopathogenic fungi accumulate at the potential infection sites of host roots by chemotaxis. The aggregated spores then adhere, encyst, germinate, and finally penetrate into the root tissues to initiate infection. Some of the host-specific attractants have already been identified. The host-specific attractants also induce cell differentiation of certain zoospores under laboratory conditions. This indicates that a signal released from the roots of the host plant guides the pest propagules for orientation and prepares them for establishing a host-pathogen relationship by necessary physiological changes. Some non-host plant secondary metabolites were found to markedly regulate behavior and viability of zoospores, suggesting that non-host compounds may also play a role in protecting the non-host plants from the attack of zoosporic fungi. We hypothesized that zoospores perceive the host signal(s) by specific G-protein-coupled receptors and translate it into responses by way of the phosphoinositide-Ca²⁺ signaling cascade. The details of the signal transduction mechanism in fungal zoospores are yet to be discovered. In this report, we review the signaling and communications between phytopathogenic fungal zoospores and host and non-host plants with special reference to Aphanomyces cochlioides.     

Fluorescein Dyes as Bacterial Stains with Special Reference to their Use for Soil Preparations

Erythrosin and rose bengal have been suggested in the past as bacterial stains, particularly in the case of the direct study of microorganisms in soil. The writers have made a further investigation of these two dyes and others of the same group (thirteen in all) to determine their relative merits for this purpose. It is found that practically all the deeper colored dyes of the group stain bacteria in pure culture satisfactorily; but that in the case of soil infusions some of the dyes have such an affinity for the dead organic matter as to obscure the bacteria present. Best results in the present work were obtained with rose bengal B; but it is pointed out that good staining effects may be obtained with the phloxines and erythrosins. The behavior of any one of these dyes when applied to a soil preparation varies according to the reaction of the material stained; and this is mentioned as a possible explanation as to why others have found better results with erythrosin than with rose bengal.     

Fluorescein Dyes as Bacterial Stains with Special Reference to their Use for Soil Preparations

Erythrosin and rose bengal have been suggested in the past as bacterial stains, particularly in the case of the direct study of microorganisms in soil. The writers have made a further investigation of these two dyes and others of the same group (thirteen in all) to determine their relative merits for this purpose. It is found that practically all the deeper colored dyes of the group stain bacteria in pure culture satisfactorily; but that in the case of soil infusions some of the dyes have such an affinity for the dead organic matter as to obscure the bacteria present. Best results in the present work were obtained with rose bengal B; but it is pointed out that good staining effects may be obtained with the phloxines and erythrosins. The behavior of any one of these dyes when applied to a soil preparation varies according to the reaction of the material stained; and this is mentioned as a possible explanation as to why others have found better results with erythrosin than with rose bengal.