The Titrimetric Determination of “lactobacillus Case1 Factor” and “folic Acid”*

Microbiological tests have aided greatly in the isolation work on “L&o!x~ciZZus casei factor,” demonstrated by Snell and Peterson in 1940 (l), and “folic acid,” the nutrient required by Streptococcus lactis R as defined by Mitchell et al. (2). It seems likely that bacterial assays will continue to play an important role in the study of these compounds, since development of chemical methods has been hampered by insufficient pure material, and animal tests are rather cumbersome and are complicated by intestinal synthesis. Assays in which Streptococcus loxtis R and Lactobacillus casei are employed have been described by Snell and Peterson (1)) Mitchell and Snell (3)) Landy and Dicken (4)) and Luckey et al. (5). The Streptococcus lactis R turbidimetric method of Luckey et al., has been found to produce reliable results, and the medium has been modified only to allow more acid production. In the case of Lactobacillus casei, reliable assays could not be obtained with media that have been published heretofore. This report presents modifications which have rendered the assay satisfactory in our hands. The effect of the method of preparing samples on their activity for the microorganisms is not discussed, nor is there any comparison of bacterial activity with animal tests. It is apparent that the present studies on fundamental aspects of the microbiological assays are necessary to facilitate the solution of these larger problems.