SUMMARYCells of Brucella abortus, strain S A -S , grown within normal guinea-pig monocytes maintained in vitro, were examined by electron microscopy. Intracellular multiplication of brucellae was followed for 48 hr. During the entire period of observation the bacteria were present in the cytoplasm of the monocytes, localized within vacuoles limited by a 'unit membrane'.No obvious ultrastructural differences (particularly in surface structures) were detected between monocyte-grown bacteria and sister cells cultivated on a lifeless medium, which might account for the known differences between the two (e.g. differences in resistance to serum bactericidal factors and in intracellular growth patterns).In spite of the large numbers of intracellular parasites present the host cells did not show evident structural modifications.Some observations made on intracellular B. abortus, strain SA-R, showed that after up to 24 hr within guinea-pig monocytes most of the bacteria had retained their morphological integrity and were indistinguishable from R organisms grown on agar,

SUMMARYAn electron microscopic investigation was carried out on thin sections of both S and R variants of Brucella abortus, strain S A : no ultrastructural differences were noted between the two variants.The cells are limited by a cell wall, comprising an outer triple-layered membrane (65-80 8. thick) and an inner homogeneous layer of variable thickness, and a triple-layered cytoplasmic membrane about 70 A. thick.The cytoplasm and nucleoplasm of brucellae are similar to those of other bacteria. A characteristic feature of these organisms is the presence of membranous structures (300-800 A. in diameter) associated with the cytoplasmic membrane. These 'peripheral formations ', which occur singly or in clusters, do not appear to arise by obvious invagination of the cytoplasmic membrane. No evidence has been obtained for the existence of capsules in virulent brucellae. INTROIIUC'l'IOISThe aim of the present investigation was to study the ultrastructure of Brucella abortus grown either on a lifeless medium or within monocytes maintained in vitro. To our knowledge no detailed study of this organism, employing present-day techniques of electron microscopy, has been published to date.The first paper in this series deals with the morphology of S and R variants of BruceEEa abortus strain S A , grown on a lifeless medium. Our interest in comparing both variants stemmed from the notion that the mutational event occurring in B. abortus, which results in a change of genotype from S to non S (e.g. R or M), is associated with a variety of phenotypic changes. These include loss of or decrease in virulence, loss of the ability to multiply intracellularly (Braun, Pomales-Ldbron & Stinebring, 1958), change in colonial morphology from smooth to non-smooth (e.g. rough or mucoid), change in surface properties resulting in agglutination, change from sensitivity to resistance to brucella phage (Stinebring & Braun, 1959), and changes in antigenic composition. These alterations, and particularly the last four, suggested that morphological changes may occur in the surface structure of the bacteria. It seemed interesting therefore to investigate whether the above phenotypic changes would be reflected in ultrastructural differences detectable with the electron microscope.

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875BRUCELLA VACCINATION necessarily represent the maximal secretory capacity of the stomach.Summary. Analyses of gastric contents collected during a 3-hour infusion of histamine (maximal stimulation) in unanesthetized, gastric fistula dogs revealed statistically significant negative correlations between "a+] and [H+], and between [K+] and [H'] . K+ output, H+ output, and C1-output were positively correlated with output of water during this infusion. [K'] and volume-rate of secretion were inversely correlated during the first hour of infusion and positively correlated during the second and third hours.