Relation of Osmotic Pressure to Availability of Synthetic Media for Streptococci.

Abstract

The osmotic pressure of the environment of an organism is believed to be an important factor affecting its metabolism. Dr. Frankel and her coworkers have made the first attempt to apply this consideration to the investigation of synthetic media. 1 These authors kept all their media isotonic with an M/6 NaCl solution. Falk, in his review of the rôle of certain ions in bacterial physiology, expressed the view that “an attempt to keep osmotic pressure constant is undoubtedly a step toward elucidation of the principles underlying the sound use of synthetic media.” 2

The work described in the present paper includes the determination of the osmotic pressures of four series of entirely different media. Media were prepared and their availability for streptococci tested by procedures already described. 3 Osmotic pressures were calculated from the freezing point depressions. The authors were aware, at the outset, of the inaccuracies in this method due to the high molar concentrations of several of the mixtures used. The errors were ignored in order to obtain figures for preliminary comparisons.

The significance of the details obtained may be brought out perhaps most clearly in the following tabulations:

In all, 46 media were used in this study. When they are divided arbitrarily into three groups on the basis of osmotic pressure, 89% of those with osmotic pressure below 50 mm. Hg. permit viability for shorter or longer periods. Fifty per cent permit viability when pressures are below 151 and above 53 mm. Hg., and 44% of those having osmotic pressures between 666 and 915 mm. Hg. permit viability. (Table I.) Similar gradations appear again when the media are divided into 5 groups. Ninety per cent of the media with pressures below 40 mm. Hg. showed growth, 88% of those having osmotic pressures between 40 and 49 mm. Hg., 50% of those having osmotic pressures above 666 and b'elow 813 mm. Hg. and 38% of the media with osmotic pressures between 817 mm. and 915 mni. Hg. (Tablle 2.)