The effect of R factors on the process of hybridization between Escherichia coli and Shigella flexneri were investigated. All of the R factors which were confirmed to be ri⁺ in crosses between E. coli strains showed marked suppression of hybridization (ri means an agent determining the effect of recombination interference). Suppression was not observed, however, when the male strains of E. coli were infected with ri^- R factors. The extent of the suppression of hybridization by ri⁺ R factors was similar to that of recombination interference in crosses between E. coli strains. From these results, a possible mechanism of recombination interference was discussed.

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The present investigation was undertaken in an attempt to determine the antigenic relationship existing between atypical mycobacteria isolated by the authors and the American strains. The following results were obtained:
1. There was some evidence suggesting that an antigenic relationship exist between mammalian tubercle bacilli and the atypical mycobacteria used in this experiment.
2. American strains 100616 and 121326 produced serologically almost the same precipitin pattern which very much resemble those produced by group 2 (1, 2, 3, 4, and 5). Therefore, it seems that these strains belong to the same serological type.
3. The P 1 antigen contains an antigenically unique part distinguishing it from the P 16 antigen.
4. All antigen preparations did not react with antiserum for Mycobacterium phlei.

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The spore formation and germination process in Bacillus subtilis were followed by electron microscopy of ultrathin sections.
At the beginning of sporulation, the cytoplasmic membrane, associated with a small amount of the cell wall material, centripetally invaginates into the cytoplasm at opposite sites near one end of the cell to develop the forespore septum. This septum is composed of two double-layers of the extending cytoplasmic membrane and of a cortical interspace, and it progressively encloses the nuclear apparatus and finally becomes discontinuous with the cytoplasmic membrane. The intracytoplasmic membrane system is present inside as well as outside the forespore, and it appears to connect to the forespore septum and membrane. The cortex is progressively deposited between the opposite layers of the forespore septum and membrane. Only after the completion of the forespore, the initial spore coat appears fragmentarilly as a dense layer in the sporangial cytoplasm peripheral to the outer forespore membrane, and it develops to a multilaminated envelope. As the forespore develops to a mature spore, the nuclear fibrils and the membraneous organelle become invisible in the uniformly homogeneous spore cytoplasm. It seems that the inner layer of the forespore membrane finally develops into the core membrane (probably the spore cytoplasmic membrane) and the outer one gradually disappears.
At the initial stages of spore germination, the cortex swells outward and is transformed to a spongy structure following partial dissolution. Immediately after this, the nuclear fibrils appear in the lighter region within the granulated spore cytoplasm, and successively the cell wall, the cytoplasmic membrane and the membraneous organelle become distinctly visible. As the dissolution of the cortex proceeds, a new vegetative cell is released, rupturing the spore coat near the equatorial portion.

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The surface structure of a strain of Fusobacterium polymorphum was studied electron microscopically employing both carbon replica and ultrathin sectioning techniques. The surface of the cell wall as revealed by the carbon replica technique showed a succession of granular protuberances. In ultrathin sectioned preparations, the cell wall consisted of two layers. The first layer consisted of a three layered structure, simulating the appearance of an unit membrane, and waved rather sharply. The innermost edge of the second layer waved lightly, and tended to be adjacent to the tips of the infoldings of the first. The diameters of the granular protuberances in carbon replicas coincided, on the whole, with the wave periods of the first layer in ultrathin sections. The cytoplasmic membrane was recognized as an unit membrane and infolded into the interior of the cytoplasm at certain places. The intracytoplasmic membrane system which bore a connection with the cytoplasmic membrane and showed diverse profiles was also observable.

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