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Volume 5,
Issue 2,
1951
Volume 5, Issue 2, 1951
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The Statistical Analysis of Slope-Ratio Assays
More LessSUMMARY: In the past, the statistical analysis of slope-ratio assays has failed to make specific tests of the validity of assumptions essential to the validity of the conclusions to be drawn, and has instead relied upon a composite test of residual variation. The technique introduced in, this paper enables the analysis of variance of assay data to be developed in a manner analogous to that customary for parallel line assays. The paper illustrates the calculations for a 5-point assay, and shows how the analysis of variance, completed with the aid of a set of orthogonal coefficients, gives the required validity tests. Similar analyses for other assay designs, symmetrical and unsymmetrical, are, briefly described, and tables of the orthogonal coefficients for 5-, 7-, 9-, and 11-point designs are given. A final section discusses the need for vatidity tests in biological assays.
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Significance of Calcium in the Fruiting of Chaetomium Species, Particularly Chaetomium globosum
More LessSUMMARY: Calcium is required by Chaetomium globosum for the normal formation of perithecia, but is not essential for vegetative growth. Calcium is at least partly replaceable by scrontium or barium. Most of the other species of Chaetomium tested responded to calcium, either in fruiting or growth, or both.
Suitable doses of calcium reproduce in a large measure the previously observed effect of jute extract on the fruiting of Chaetomaum species. The presence of calcium in jute extract was established.
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Polysaccharidases of Group A Streptococci
More LessSUMMARY: Proteinase produced by Group A streptococci was associated with a decrease in hyaluronidase production which was not related to any other known environmental condition. The concentration of proteinase which was correlated with decreased hyaluronidase production was constant for a given strain. Inactive polysaccharidase components in cell-free filtrates were converted to active form by a number of different agents, namely, sodium sulphite, zine and calcium ions, auto-claved broth and pantothenie acid. Bacterial dextran, pectin and inulia were depolymerized by cell-free filtrates and by partially purified enzymes derived from Type 4, Type 22 and Type 2 strains. Depolymerase was associated with hyaluronidase and amylase in biologically active material prepared by fractional precipitation.
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The Virulence of Haemophilus pertussis for Mice by the Intranasal Route
More LessSUMMARY: Freshly isolated strains of Haemophilus pertussis vary considerably in their virulence for mice when tested by the intranasal route; this variation is continous and must be regarded as a quantitative not a qualitative character. In order to titrate virulence it is necessary to achieve and maintain a standard technique with cultures and to use ‘standard’ mice kept under standardized conditions. It was not possible to show a correlation between virulence (as measured by the LD50) and either the viable count or the presence of toxin of haemagglutinin in the suspensions used in the virulence test. Nor was it possible to show any correlation between virulence and the ‘age’ of the culture, either in number of subcultures, time elapsing between swabbing and testing, type of swab or duration of illness (up to three weeks) when the swab was taken. Some strains kill mice more quickly than others; this ability is attributed to a ‘quick-killing factor’.
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The Isolation of Deoxyribonucleic Acid from Virulent and Avirulent Strains of Haemophilus pertussis
More LessSUMMARY: Haemophilus pertussis cells contain a relatively large amount of deoxy-ribonucleic acid which may be extracted from the organisms with 2% sodium cholate.
A method is described for the isolation of deoxyribonucleic acid from the mechanically disintegrated organisms, which yields an apparently undegraded preparation free from ribonuclcic acid and protein, but containing a polysaccharide component, probably in combination with the nucleic acid. This finding gives further evidence of the differences in biological properties of virulent and avirulent strains such as agglutinability by type-specific serum. precipitability by aluminium phosphate, and solubility in bile and sodium hydroxide.
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The Intracellular Growth of Fowl-Plague Virus
More LessThe changes in fowl-plague infected tissue cultures have been investigated by the phase-contrast, and electron microscopes. The nucleolus of infected cells first increased in size and then became granular and highly refractile, finally disintegrating into fragments about 64 hr. after infection. After 36 48 hr., when the inclusions were already developed, filaments were found, usually in bundles, possibly having escaped from the nucleus into the cytoplasm; a few filaments showed segmentation into spherical bodies and shorter filaments. A possible life cycle is suggested for the virus: first, penetration of the nucleus and growth within it, then extension into the cytoplasm in a filamentous form, and eventual segmentation of some of the filaments into elementary bodies.
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Cell Structure of Corynebacterium diphtheriae
More LessSUMMARY: When examined by phase-contrast microscopy living diphtheria bacilli generally appear fairly transparent. They are sometimes unicellular but are frequently divided into compartments by readily visible cross-septa. In gravis and mitis strains the cross septa are usually few in number and the compartments long, but in intermedius strains there are often many cross-septa, and the organism may resemble a chain of cocci fused together. Club-shaped cells with swellings are seen in untreated living cultures as in fixed and stained preparations of killed bacteria, and occasionally branched forms are encountered. Undivided filaments sometime occur in magnesium-deficient cultures, whilst in magnesium-rich cultures cells with numerous cross-septa are scanty. The presence of magnesium salts has some protective effect against the growth-inhibition produced by beryllium salts. In cultures containing selenite or tellurite the bacteria become red or black, granules containing selenium and tellurium occur and areas resembling chromatinic structures may be seen.
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Effect of Cultural Conditions on Bacterial Cytology
More LessSUMMARY: Phase-contrast microscopy of living bacterial cells under appropriate conditions is of value in determining cellular structure, bacterial nuclear processes, methods of division and the effects of cultural conditions. Different species of bacteria differ in their methods of division (for example by constriction or by eross-septation) and in their apparent internal structure. Considerable differences may be seen also in the same organism grown under different cultural conditions. The same species of bacteria may exist as short oval bacilli in an agar medium and long-chained or filamentous forms in broth, with equally characteristic differenees in the distribution of refractile material within the cells. The incorporation of special chemical compounds in the culture medium raises the possibility of vital ‘staining’ by the deposition of refractile material in defined sites within the bacteria during growth, thus rendering visible by phase-contrast microscopy certain cellular structures in living bacteria. The inclusion in culture media of tellurite and selenite has this effect of showing up internal structure in the bacteria grown in their presence. Apart from the possibility of developing new procedures for detecting internal structure, phase-contrast microscopy is of use in evaluating fixation and staining methods by comparing the fixed and stained specimens with living cells, and thus recognizing distortions and artefacts introduced by preparative treatments.
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The Identity of Proteus hydrophilus Bergey et al. and Proteus melanovogenes Miles & Halanan, and their Relation to the Genus Aeromonas Kluyver & van Niel
More LessSUMMARY: Proteus melanovogenes, originally isolated from black-rot in eggs, does not differ from Pr. hydrophilus, the cause of red-leg in frogs, more than different strains in each species differ from one another; and the two species may be considered as identical.
Both ‘species’ resemble Aerobacter liquefaciens Eeijerinck, Pseudomonas fermentars von Wohlzogen Kuuml;hr and Ps. ichthyosmia. The divergences from a common type displayed by these species may be sufficient to warrant the preservation of some as separate species, some as varieties, but all strains of this type with the property of producing 2:3-butanediol from glucose should be allotted to the genus Aeromonas in the Pseudomonadaceae, as recommended by Kluyver & van Niel (1936).
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The Mouse Pathogenicity and Toxicity of Proteus vulgaris
More LessSUMMARY: The LD50 for mice of twenty-one strains of Proteus vulgaris from human infection ranged from 2 to 600 million living bacilii. Mouse-virulence was not associated with the severity or the site of infection in the human subject.
The relatively high virulence of some strains was not due to any peculiar demonstrable toxicity of the cell-substance, because killed cells of high and low virulent strains were about equally toxic. The toxicity appeared to reside in a predominantly lipe-polysaceharide fraction, immunologically similar to the antigen characterizing the somatic surface of recently isolated strains.
This investigation was made to find whether strains of Proteus vulgaris isolated from infections in man could be distinguished by a laboratory virulence test, and whether virulence could be correlated with any other microbiological character of the strains.
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Isolation of a Bacterium, Producing Propionic Acid, from the Rumen of Sheep
More LessSUMMARY: A strictly anaerobic microcoecus which produces acetic acid, propionie acid, carbon dioxide, and hydrogen by fermentation of lactate was isolated from the rumen of sheep. It failed to ferment sugars and was identified as Veillonella gazogenes. Its significance in ruminant digestion is uncertain, but a characteristic reaction of this organism, the decarboxylation of succinie acid to yield propionic acid and carbon dioxide, appears to be important in the rumen. This reaction was studied by the Warburg technique with washed suspensions of rumen bacteria.
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The Mechanism of Propionic Acid Formation by Veillonella gazogenes
More LessSUMMARY: The mechanism of propionic acid formation from lactate by Veillonella gazogenes is according to the scheme:
CO2
lactate → pyruvate → cxaloacetate → malate → fimarate → succinate → propionate + CO2
The evidence for this scheme is: (a) Washed suspensions of the organism grown on lactate attack, under anaerobic conditions, pynivate, oxalacetate, l-malate. fumarate and suecinate, but d-tartrate. (b) Organisms grown on d-tartrate attack it and all the substances listed in (a) except lactate. (c) Succinie acid is quantitatively decarboxylated to propionic acid and carbon dioxide, (d) The amount of propionic acid produced from lactate is influenced by the CO2 concentration in the medium. (e) CO2 is fixed in the carboxyl group of propionic acid during fermentation of lactate.
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The Mechanism of Propionic Acid Formation by Propionibacteria
More LessSUMMARY: The main mechanism for propionic acid formation by organisms of the genus Propionibactcrium is by the decarboxylation of succinic acid. The varying ratios of propionic to acetic acid reported in the literature as a result of the fermentation of glucose are attributed to differences in carbon dioxide tension and in the initial and final pH values of the cultures.
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The Ability of Single Phage Particles to Form Plaques and to Multiply in Liquid Cultures
More LessSUMMARY: The results of testing a bacteriophage to a strain of clover nodule bacteria using young (1 day) and old (5 days) bacterial cultures both fit to the hypothesis that phage multiplication can be initiated by single phage particles. As the same phage preparations gave more plaques on solid media and higher proportions of liquid cultures in which phage multiplication could be detected, with young than with old bacterial cultures, the fit to the hypothesis is not an evidence that every single phage particle will multiply. It may be so when young bacterial cultures are used, although there is no positive evidence for it. With older bacterial cultures definitely only a proportion of viable phage particles succeed in starting phage multiplication, the proportion decreasing with the increasing age of bacterial cultures used for testing.
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An Antibiotic Assay Tray
More LessSUMMARY: The construction is described of a tray made of an age-hardening aluminium alloy and toughened glass for use in antibiotic assays on agar media.
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Nitrification of Oxime Compounds by Heterotrophic Bacteria
More LessSUMMARY: Production of nitrite from the oxime of pyruvic acid was observed with three groups of heterotrophic soil bacteria: Nocardia corallina, Alcaligenes spp. and Agrobacterium spp. The first could nitrify up to 64% of the oxime-nitrogen in an inorganic salts solution, the second and third up to 43 and 36%, respectively. Glucose inhibited nitrification by stimulating the synthesis of cell substance; nitrification by Nocardia corallina ceased at C:N ratios above 20:1. Approximately 75– 90% of the oxime-nitrogen was recovered as nitrite + cell-nitrogen in cultures of Nocardia and Alcaligenes spp. In peptone medium Nocardia corallina converted the oxime almost quantitatively to nitrite; the rate of nitrite production was parallel with that of cell multiplication. Alcaligenes and Agrobacterium spp. caused a further removal of the nitrite in peptone medium, the latter organism by denitrification. The oxime of oxaloacetic acid was readily nitrified by Alcaligenes spp. Acetoxime was only nitrified to a slight extent and free hydroxylamine apparently not at all. Several other organisms, of which Corynebacterium equi was a possible exception, did not nitrify pyruvic acid oxime.
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A Re-investigation of the Root-Nodules of Species of Elaeagnus, Hippophae, Alnus and Myrica, with Special Reference to the Morphology and Life Histories of the Causative Organisms
More LessSUMMARY: Root-nodules of Elaeagnus spp., Hippophae rhamnoides, Alnus glutinosa and Myrica gale are modified lateral roots. The enlarged cortical cells of an actively growing nodule contain the endophyte in several stages of development, The apical meristem is free from infection but the cells just behind it show a plasmodial stage. In older parts of the nodules, spherical vescles are formed in species of Elacagnus, Hippophae and Alnus and club-shaped bodies in Myrica and from these small, bacteriod-like granules are produced. There is some evidence that granules formed in different host cells fuse in pairs and possess some ability to migrate within the nodule and into the soil. No definite hyphae can be seen in any of the nodules, but well-marked protoplasmic strands or lines of flow are present, particularly in the endophyte of Myrica.
The controversial views of earlier writers are discussed, and it is concluded that the nodule organisms are members of the Plasmodiophorales.
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A Selective Medium for Bacillus anthracis
More LessSUMMARY: A nutrient medium containing lysozyme and hacmatin is described which permits free growth of B. anthracis while suppressing more than 95% of other Basillus spp. in soil.
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