THE EFFECT OF HYDROGEN ION CONCENTRATION ON THE TOXICITY OF ALKALOIDS FOR PARAMOECIUM

¹ From the Pharmacological Laboratory, Washington University, School of Medicine, St. Louis

1. The limits of hydrogen ion concentration within which Paramoecium can live twenty-four hours have been found to be approximately 1 x 10^–9.6 and 1 x 10^–5.0.

2. The magnitude of the effect upon toxicity of definite changes in hydrogen ion concentration has been determined for a number of alkaloids.

3. The effect of changes in hydrogen ion concentration upon toxicity has been found to vary with the dissociation constant of the base. The free, undissociated base is apparently responsible for the toxicity.

4. The effect of hydrogen ions upon toxicity is evidently due to an action upon the drug. If there is any direct action upon the resistance of the cell it is very slight at the concentrations studied.

It is a great pleasure to me to acknowledge my indebtedness to Dr. E. K. Marshall, Jr. for the suggestion and supervision of this piece of work, and to offer him my sincere thanks for the help and advice he has given me throughout.