Critical Concentrations of Bioses.

Abstract

The observations on yeast growth which have been recorded by numerous workers, together with the results reported here, seem to require some extension of the theory of “bios” originally stated by Wildiers,₁ viz., “That a substance of unknown composition, or bios, is indispensable for the development of yeast.” For the development of some species of yeast at least, a certain minimal concentration of a substance or substances is indispensable. Moreover, the following results show that this minimal concentration may be very critical, i. e., a given yeast species may be very sensitive to a small diminution in the concentration of bios below the minimum value.

Critical Concentration of Bios. The following type of experimental result has led to the postulation of a theory of “critical” concentrations. A series of 7 different concentrations of “bios” (in the form of a 70% alcoholic extract of autolyzed yeast, from which the alcohol had been evaporated) in a basal salt-sugar medium, was inoculated with varying quantities of yeast cells. After 5 days'rncubation at 25° C. a concentration of cells (constant within 22%) was observed corresponding to each “bios” concentration—except the smallest. In the latter case (0.025 mg. of bios per cc.) this constancy was absent, and the smaller seedings attained a final concentration which was 72% less than that with the largest seeding. The figures are given in Table I.

If the concentration of bios falls below a certain minimum (in the above experiment .045) then there is a marked difference between the behavior of large and small seedings. Further investigation is necessary before any explanation of this effect can be given. However, the determination of the minimum or “critical” concentration for any given preparation of bios may be made a simple means of gauging its potency.