Successful in vitro primary antibody formation to sheep red blood cells (SRBC) was obtained with normal mouse spleen cell suspensions cultured in the stationary state and in an atmosphere of 10% CO₂ in air. The response was measured by an increase in the number of hemolytic plaque forming cells and it reached about 30-150 per 10⁶ recovered cells by the 4th day of culture. The immunological activity of the spleen cell suspension was highly dependent on the cell-concentration of the suspension used for the culture, antigen dose to be added, the lot of calf serum employed in the culture medium and so on. The data obtained by the present in vitro studies on antigen dose, kinetics, and immunologic specificity indicated close similarities between the in vitro and in vivo response. Addition of "late" anti-SRBC serum, which contained mainly 7 S anti-SRBC antibody, to the cultures suppressed extremely the immune response in vitro, and the data on the suppressive effect of specific antibody are also consistent with those obtained by in vivo studies.

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In vivo uncoating of tobacco mosaic virus (TMV) was studied ,and evidence for the presence of TMV-RNA completely free of coat protein was obtained. Complete uncoating of TMV takes place very early after infection in the particulate fraction, probably in the nucleus. In contrast, partial uncoating took place with most of the viruses inoculated and only a small amount of TMV was uncoated completely. The efficiency of uncoating was comparable to those viral infections measured by bioassay. Combining the results obtained and including previous findings, a two-step uncoating reaction was suggested; namely, initiation of uncoating taking place in the cytoplasm and a further uncoating in the particulate fraction.

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The opsonic effect of specific antibodies against Salmonella typhimurium wild-type LT2 strain and its mutant strains possessing various cell wall polysaccharides was examined as to the in vivo clearance of the bacteria from the blood or peritoneal cavity of mice and also the in vitro phagocytic process of the bacteria by mouse peritoneal macrophages. Clearance-rate of the strains, which possessed a repeating polymer of O side chain (tetrasaccharide sequence of abequosyl-mannosyl-rhamnosyl-galactose) or one unit of the tetrasaccharide (rfc mutant strain) in their cell wall, was greatly enhanced by the administration of specific antiserum to mice prior to infection. The opsonic effect of the specific antiserum to these strains is undoubtedly attributed to the antibody directed to the O side chain polysaccharide, while in the clearance of the rfc mutant strain the antibody to R-core polysaccharide also was effective. The mutant strains, which lack the O side chain in their cell wall, were cleared so easily that the opsonic effect of the antisera could not be assessed. The study of in vitro phagocytosis of ³²P-labeled organisms by macrophages also demonstrated a close correlation between the opsonic activity of the specific anitserum and the cell wall polysaccharide constitution of the organisms. Furthermore, it was found that rough mutants are more easily fragmented within phagocytic cells than the wild-type strain cells.

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The chloramphenicol-resistance (Cml^r) determined by an unstable and nontransmissible R factor, R9-4, was lost at high frequency during the subculturing of the R9-4⁺ bacteria. Two stable Cml^r strains were isolated after long term storage of Escherichia coli K12 harboring R9-4. The cml genes governing Cml^r were found to be integrated into the E. coli chromosome: one of them linked closely with met B locus [9] and the other did not. When the R9-4 was introduced by transduction into an HfrC strain and a sexual cross was done between HfrC R9-4⁺ and F^-, Cml^r of R9-4 was transferred at low frequency and the cml genes integrated into the chromosomes were easily obtained in the F^- exconjugants. It was found that they had been integrated into various regions of the E. coli chromosome, near lac, ara, mtl, and gal genes.

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A mutant strain MS537-59 was isolated from Staphylococcus aureus MS537, in which leucomycin, in addition to erythromycin, was an active inducer for macrolide resistance. By pretreatment with subinhibitory concentrations of leucomycin, MS537-59 acquired a high resistance to both macrolide antibiotics as well as lincomycin. Erythromycin exhibited the highest activity as inducer followed by leucomycin. An acyl group on the mycarose and an aldehyde group were found to be needed for inducer activity by leucomycin.

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When Escherichia coli or its endotoxin was inoculated into mice intraperitoneally a few hours before or after the intravenous inoculation with Nocardia asteroides, an increase in susceptibility to nocardial infection occurred which resulted in the early death of mice with numerous heart nodules. When the E. coli was given 48 hr before the Nocardia infection a state of decreased susceptibility was noted which lasted for a few days. Conspicuous heart nodules were perhaps caused by the multiplication of Nocardia cells in the heart which had been damaged by the toxic action of E. coli (endotoxin).

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The transforming capacity of SV40 was more resistant to UV-inactivation than its infectivity, and the target size of the SV40 genome required for transformation was estimated as one fourth of the whole viral genome. The capacity of adenovirus 12 to produce tumors in hamsters, estimated by the dilution endpoint, was far more resistant to UV-inactivation than its infectivity. T antigen was always positive in cells transformed by UV-irradiated SV40 and in tumor cells induced by UV-irradiated adenovirus 12.

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A soluble antigen of infectious bronchitis virus was detectable by immunodiffusion in chorioallantoic membranes of embryonating chicken eggs 12 hr after infection. The antigen was inactivated by heating at 60 C for 10 min, and by digestion with trypsin, and was not destroyed by DNase or RNase. The antigen was partially inactivated by treatment with acetone and chloroform but only a slight or no inactivation was observed by treatment with ether. The antigen was partially precipitated with ammonium sulfate. In sucrose gradient centrifugation the antigen sedimented slightly faster than chicken hemoglobin.

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