STUDIES ON THE PHYSIOLOGY OF THE EUGLENOID FLAGELLATES

III. THE EFFECT OF HYDROGEN ION CONCENTRATION ON THE GROWTH OF EUGLENA GRACILIS KLEBS

¹ DEPARTMENT OF BIOLOGY, UNIVERSITY COLLEGE, NEW YORK UNIVERSITY

1. The amount of growth of Euglena gracilis in cultures of different pH values has been measured quantitatively at the end of 8-10 days and has been estimated macroscopically at the end of seven weeks.

2. It is demonstrated that bacteria-free cultures of Euglena gracilis, in a solution of casein decomposition products and under conditions which allow mixotrophic nutrition, show, at the end of 8-10days, a high growth rate between pH 3.9 and pH 7.5 with a maximum at about pH 6.6, and a uniformly decreasing growth rate with increasing alkalinity between pH 7.5 and 9.9.

3. It is also demonstrated that at the end of seven weeks the most growth is found to have occurred in the alkaline range, and that the maximal density of population is at about pH 7.5.

4. It is shown that the results of previous investigators, heretofore considered contradictory, may be explained on a basis of the time relationships involved.

5. The existence of a proteolytic enzyme in cultures of E. gracilis is confirmed.