THE REACTIONS OF PARAMECIUM TO SOLUTIONS OF KNOWN HYDROGEN ION CONCENTRATION

¹ THE UNIVERSITY OF CHICAGO AND WABASH COLLEGE

1. The reactions of Paramecium caudatum to solutions of known hydrogen ion concentration were studied.

2. The colorimetric method of determining hydrogen ion concentration was used but was checked by a series determined both colorimetrically and by Youden's potentiometer.

3. The acids used were: hydrochloric, nitric, sulphuric, carbonic, formic, acetic, citric, picric, pyrogallic and tannic.

4. The waters used were: Chicago tap-water, Whitman well water, Hull well water, Crawfordsville (Ind.) tap-water, distilled water, Chicago tap-water made carbonate-free, Whitman well water made carbonate-free, and Hull well water made carbonate-free.

5. In these experiments only Paramecia from alkaline cultures responded positively to acidified solutions.

6. Paramecia from alkaline cultures react positively to all H-ion concentrations higher than that of their culture to pH 5.0 (4.83 potentiometer reading) inclusive, when the H-ion concentration is produced by the inorganic acids—hydrochloric, sulphuric and nitric acids.

7. Organic acids, such as acetic, formic, carbonic and citric, which are not toxic in this pH range elicit responses similar to those caused by the inorganic acids.

8. Pyrogallic and tannic acids are toxic to Paramecia in solutions with concentrations of pH 4.8 through pH 5.8 but the organisms enter these waters and die as a result.

9. Paramecia react to acidified water from which all carbonates have been previously removed. This is an indication that Paramecia react to the hydrogen ion "per se" and not to carbondioxide.

10. Paramecia are better able to live in solutions of high H-ion concentration than many have supposed.

11. Sulphonphthalein indicators, when used in no stronger concentration than necessary for pH determinations, are not harmful to Paramecia.

12. Paramecia will not react positively to weakly acid solutions when the temperature is below 21 degrees C.

13. No new evidence was obtained as to the nature of the mechanics of the reaction of Paramecia to acids.

14. Paramecia gather in clumps when they react to acidified solutions containing NaOH.

15. In one of the four types of water tested acidified water did not elicit positive responses from Paramecia. No reason is offered for this exception.