1. Susceptibility (minimal inhibitory concentration M.I.C.) of 132 strains of Pseudomoas aeruginosa to Colistin sulfate by serial plate dilution method was 2.92±1.61 mcg/ml. More. than half of Pseudomonas aeruginosa strains were inhibited in the concentration of 12.5 mcg/ml of Colistin methanesulfonate. Polymyxin B was as or slightly less active than Colistin sulfate.
Cross-resistance was noticed between Colistin (sulfate and methanesulfonate) and Polymyxin B. Natural resistant strain of Pseudomonas aeruginosa to Colistin and Polymyxin B was quite difficult to be found out in present study by the usual measuring method for suscehtibility, but this method must be improved.
2. In vitro development of resistance of Pseudomonas aeruginosa to Colistin was, readily demonstrated, but the in vitro induced resistant forms were not stable and reverted in the absence of the antibiotic. In vivo development of resistance of Pseudomonas aeruginosa to Colistin was supposed to occur in clinical practice, too. It was believed that the resistance was developed by the ability of adaptation of Pseudomonas aeruginosa to Colistin, but the mechanism of the adaptation to the antibiotic was not made sure in present study.
3. Titration end point of M.I.C. depended on the size of inoculum: in vitro activity of Colistin was decreased by increasing the size of the inoculum. This phenomenon was seen not only in Colistin and Polymyxin B, but also in Streptomycin, Kanamycin, Tetracycline and Chloramphnicol

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In Comparison with Wassermann-Test carried out hiertofore using caldiolipin antigen, RPCF-Test which has been recently introduced in our Country as a method of serodiagnostic test for syphilis seems to show a higher specifity because of the treponemal antigen. No particular false-positive reactions have been reported in non-syphilitic diseasesexcept in cases of Yaws, Pinta and Leprosy.
As already described in our previous report, a number of false-positive reactionswere found in pregnancy, tuberculosis and cancer, i.e. apparently non-syphilitic diseases.
In this paper influences of different antigens and techniques on the outcome of the test were investigated and the results were as follows:
1. From the differennce in antigens and techniques in the RPCF-Test, the results are considerably influenced, and false-positive reactions might be induced.
In case of pregnancy, it may be more severely influenced by the difference in antigens than by that in techniques, in contrast to the tuberculosis. On the other, in case of cancer, severe influences by both of them could be observed.
2. Regarding the sensitivity in RPCF-Test, the modified Kolmer's methoed has shown the most excellent result, followed by the Ogata-over-night method and the Ogata-one-hour method.
On the other hand the frequency of false-positive reactions was also according tothis order.
3. The majority of the cases which showed positive reactions in both of the Modified Kolmer's method and the Ogata-over-nght method whilst non-reactive in the Ogata-onehour method, could be found among the cases which were diagnosed as latent syphilis and fully treated.
4. Regarding the antigen, the domestic RPCF antigen has shown a higher sensitivity compared with the Organon's antigen (Holland), whilst the frequency of the false-positive reactions has been higher in the former than in the latter.
From this view-point, further investigations on the selection of the strain and the purification method should be required.

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