The sensitivity of El Tor and Asiatic cholera vibrios to various antibiotics was tested by means of “disk” method. The vibrios of both types were found to be sensitive to all antibiotics, tested. ie., polymyxin B, colistin, leucomycin, tetracycline, kanamycin, erythromycin, chloramphenicol and streptomycin, but the sensitivity was much lower in El Tor vibrios than in asiatic cholera vibrios except that to streptomycin.
Though the difference in sensitivity, expressed in the width of inhibitory zone, between both types was “highly significant” for polymyxin B, colistin, leucomycin, tetracycline and kanamycin, the distribution curves of sensitivity for both types were considerably overlapped. For this reason, it is thought to be difficult to distinguish these vibrios only by “disk” method.
The difference of the sensitivity to polymyxin B between the vibrios of both types was also determined by serial dilution technique. The limiting concentration of polymyxin B for the growth of Asiatic cholera vibrios was under 50 u/ml, mostly under 25 u/ml, but for El Tor cholera vibrios hat was over 100 u/ml, mostly over 200 u/ml. Therefore, it is concluded that the use of peptone water containing 100 u/ml of polymyxin B is useful for the differentiation of these vibrios.
The effect of the size of inoculum to the limitig concentration as determined by serial dilution method was discussed.

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(1) JBE virus, Gi strain, cultivated serially in trypsinized hamster kidney cell cultures was tested for immunogenic potency for mice, rabbits and monkeys. Undiluted culture fluid harvested from infected tubes was used as “crude virus.” “Formalinized virus” was prepared by mixing infected culture fluid with formalin at a final concentration of 0.1% and holding the mixture at 4°C for 2 weeks. Active virus, purified partially by the cellulose column chromatography or fluorocarbon deproteinization, was designated as “purified virus.” Virus which was purified and inactivated or reduced in mouse-infectivity by being treated with trypsin or lipase, was called as “enzyme treated virus.”
(2) Active virus, either crude or purified, was apparently non-pathogenic for mice through the intramuscular route, or for rabbits through the intravenous route. In monkeys (Macaca fuscata) in-jected intracutaneously with active virus, leucopenia with relative lymphocytosis, both of slight degrees, was noted; no other signs, such as hyperpyrexia, poor appetite, etc., were apparent.
(3) Mice were injected intramuscularly with active or formalinized virus and were subsequently challenged by the intracerebral inoculation of mouse-passaged Gl strain virus. Survival ratios were significantly higher among immunized mice than among control non-immunized mice. Little difference was noted between results obtained using active or formalinized viruses.
(4) Rabbits injected intravenously with active or formalinized virus produced neutralizing (NT) and complement-fixing (CF) antibodies specific against the original mouse-passaged JBE virus. Following the second injection given 2 weeks after the first injection, NT indices were 100 to 1, 000 and CF titers 1: 16 to 1: 64. Antibody levels increased rapidly after the third or fourth injection which was given 15 to 50 weeks later. There was little difference in the pattern of serological response between the animals injected with active or formalinized virus.
(5) In monkeys injected intracutaneously with active virus, NT and CF antibodies were produced. The increase of antibody titers was somewhat gradual after the first injection, and was more rapid after the second or third injection. Antibody titers of monkeys inoculated with active virus were higher than those of monkeys receiving formalinized virus. The results appeared to indicate that active virus was more effective than formalinized virus in stimulating antibody production in monkeys.
(6) Purified virus stimulated rabbits, and monkeys to produce the specific antiviral antibodies (NT and CF) as did crude virus. Antibody development in rabbits inoculated with enzyme-treated virus was significantly lower and more irregular; in some animals no antibody was produced. It appears that trypsin and lipase have an effect upon substance (s) controlling the immunogenicity of JBE virus.

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