[Investigations of some metachrome-yellow-preparations as an basic ingredient for metachromgelb-wasserblau-laktose-agar (Gassners medium) (author's transl)].

Experiments with 5 commercial- and 4 testpreparations of Metachrome Yellow have been conducted. Results of this investigations show that the value of Gassners Medium is depending on the quality of the inhibitory substance. The microbiologically active substance (inhibition of grampositive bacteria and prevention of swarming of Proteus) was chemically identified as "Beizengelb GT Color Index 14025" correlating with CI Mordant Yellow I. Test sample II of CHROMA-GESELL-SCHAFT, STUTTGART is recommended as the best "Metachrom-Yellow for preparation of Gassners-Medium Now. Presumable this medium was modified repeatedly after its introduction in bacteriology in 1918 by Gassner. This can be an explanation for the different evaluations of Gassners medium and also for the numerous experiments which have been conducted to modify the medium. Indentity control of chemicals used in microbiology is done by thin layer and paper chromatography. This control should be done in cooperation with chemists more frequently than before.