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Protozoa and bacteria have been shown to undergo similar growth phases in cultures (Hall, '53; Wilson and Miles, '46), and comparable variations in average cell volumes and e,nzyme production have been reported for different periods in the growth of populations (Ormsbee, '42; Wilson and Miles, '46). It was felt that a consideration of such variables might produce significant data bearing on problems of adaptation. As a basic procedure, it was decided to trace changes in volume which might occur when Protozoa and bacteria were transferred to various fresh media from stock cultures in diff erent phases of growth. MATERIALS AND METHODSThe organisms employed were Euglena gracilis (Damon strain, Astasia louzga, Chilowtonas paramecium (Pringsheim strain), Tetrahymefia pyriformis (strain H), Escherichia coli communis, E. coli mutabilis (strain ML-3b), Streptococcus faecalis (strain ATCC 8043), Lactobacillus fermefitunz (strain ATCC 9833), and L. Zeichnzanuzii (strain ATCC 7830).

SUMMARY. Transfers of Euglena gracilis to fresh media gave rise to increased volumes of the flagellates, the magnitude of expansion varying with temperature, pH, osmotic pressure, and number of nutritional particles in the medium. Expansion was accompanied by decreased protoplasmic density and increased intracellular solids and water. When the population density of the flagellates was more than optimal, competition for substrates was reflected in reduced maximum volume. Below the optimal range, a similar decrease in maximum volume was observed.