An unstable mutant R factor conferring only chloramphenicol (CM) resistance was obtained by spontaneous segregation. After storage in broth culture, a stable CM-resistant mutant was obtained and its CM-resistance could not be cured by treatment with acriflavine or transduced to a recombination-deficient strain of Escherichia coli K12. Recombinational analysis indicated that the cml gene governing CM resistance had been integrated into the E. coli chromosome and closely linked with met B locus. The cml gene was co-transduced with both met and arg markers by phage P1, and the linkage order was considered to be mtl-cml-met-arg-thi. When the strain carrying this chromosomal CMresistance was infected with a transferable R (TC) factor capable of conferring tetracycline (TC) resistance, the CM-resistance became transferable by conjugation. This mechanism is considered to account for the formation of the recombinant R (TC.CM) factor.

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Lowered peripheral lymphocyte count, reduced serum antibody response and partially reduced protection against infection with virulent strain of Salmonella enteritidis after immunization with live vaccine of S. enteritidis were observed in mice thymectomized at birth. However, the cellular resistance, which was observed in vitro in peritoneal macrophages from immunized animals, was not found to be reduced by neonatal thymectomy of mice. From these facts, the immunological dependence of cellular immunity on thymus in neonatal life was discussed.

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Fifty-one strains of enteric bacteria isolated in 1966 from patients at the Boston City Hospital were studied for the distribution of R factors. Twenty strains were found to carry transmissible drug-resistance factor "R" The strains harboring R factors included Escherichia coli, Aerobacter, Klebsiella, Proteus and Serratio. This report confirms similar studies in suggesting that R factors are widely distributed in enteric bacteria isolated in the United States.

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Antibody formation in vitro was studied using erythrocytes (RBC) as antigen and immunocytoadhesion as the technique for detection of antibody-forming cells. Spleen cells (SPC) of nonimmune mice gained the ability to produce antibody after treatment with ribonucleic acid (RNA) preparation extracted from allogeneic mice immunized with xenogeneic or allogeneic RBC. It was also found that a small proportion of SPC from individual mice of certain strains formed antibody against autologous RBC when the cells were treated in vitro with RNA preparation obtained from the spleen of an allogeneic mouse immunized with RBC of that individual. No converting ability was observed in the RNA preparation from spleen of nonimmune autologous or allogeneic mice. The converting activity of immune RNA preparation was shown to be sensitive to ribonuclease treatment. These evidences exclude the possible contribution of antigen or fragments thereof in the RNA preparation to the induction of antibody formation in RNA recipient cells.

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Nontransferable drug resistance was acquired by conjugal transmissibility when mixed cultivation was applied to many isolates of the Enterobacteriaceae. The genetic element able to confer transmissibility on nontransferable drug resistance, was henceforth termed the transfer (T) factor. Genetic studies showed that there are three mechanisms involved in the acquisition of transferability of otherwise nontransferable drug resistance; (I) transfer of the drug resistance determinant on chromosome along with the transfer of host chromosome by T factor, (2) transfer of the nontransferable R factor by complementation with T factor, (3) formation of recombinant between the T factor and the drug resistance (γ) determinant. The recombinant Tr factor was transferred as a single unit by the conjugal process, and was capable of conferring drug resistance. It was transduced jointly with bacteriophage P1 as a single unit in Escherichia coli.

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To solve the problems of the multiplication and invasion of Candida albicans in the alimentary tract, germ-free mice were orally inoculated with C. albicans and the an-tagonistic effect of superinfection with Escherichia coli was examined. C. albicans could easily be established in the alimentary tract of germ-free mice by inoculation with less than 10 organisms, whereas in the alimentary tract of the SPF mice, having normal bacterial flora, C. albicans could not establish even after inoculation with an overwhelm-ing dose. In germ-free mice large numbers of the inoculated candida were excreted in the feces throughout the observation period of 130 days, without affecting the conditions of the mice. By histopathological examination of these mice only one mouse showed microabscesses with leukocytic infiltration accompanied by hyperkeratosis and acanthosis in the epithelium of the forestomach. However even in this mouse no invasion of candida cells into the acanthotic squamous cell layer was seen. After inoculation of the mice who had already E. coli in their gut as a monocontaminant with C. albicans, or even after inoculation of E. coli to the mice harboring candida as a monocontaminant, E. coli always outnumbered C. albicans. In the former case candida were even completely eliminated from the mice within few days. Thus, it appeared that in the alimentary tract of the mice, E. coli have the capacity to antagonize to C. albicans.

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Peritoneal macrophages from mice, which had received an RNA fraction extracted from spleens of mice immunized with live vaccine of Salmonella enteritidis, were found to resist in vitro infection with heterologous species of Salmonella as well as the homo-logous one, but were susceptible to Mycobacterium tuberculosis. Cellular antibody demonstrated in peritoneal exudate cells from the immunized mice and from the im-mune RNA-treated mice was shown to react to these Salmonella but not to M. tuber-culosis. The relation of cellular resistance and antibody in the restricted cross-protection of immunized mice in experimental salmonellosis is thusly demonstrated.

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Relationship between K agglutinogenic factors of Bordetella pertussis were analyzed by agglutinin-adsorption tests. Factors 1 and 3 corresponded to L agglutinogen, while 2 and 4 corresponded to S agglutinogen. The experiment also indicates that B. pertussis phase I strains belong to a single serotype, while types 1-2-3, 1-2, 1-3 and 1 strains belong to the author's intermediate phase which probably arose from phase I parents. Strains isolated by us in 1952 to 1953 were type 1-2-3-4 which possessed both L and S, but a few strains isolated in 1962 and 1966 were type 1-3. The occurrence of such a defect in antigens was discussed. A single phase I vaccine seemed to give enough protection against various serotypes of pertussis organisms.

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The occurrence of immunoglobulin classes of serum antibody in response to natural infections with myxo- and pseudomyxoviruses among infants and children was investigated. Two types of the 19S antibody response have been demonstrated. In the first type, in which are included the measles and mumps virus infections, the 19S antibody appeared dominantly as a primary response to the virus infection. In the second type, which includes the influenza, parainfluenza and RS virus infections, the 19S antibody was either not detectable or produced in a limiting amount in infants even at an early stage of the illnesses. A possibility was discussed that production of the 19S antibody in response to the infection with myxo- and pseudomyxoviruses may be primarily determined by the nature of virus infection itself, particularly the presence or absence of a viremia.

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