The Relation OfSpirostomum AmbiguumTo The Hydrogen ION Concentration (Alkaline Range)

1. A recovery method is described for determining the survival time of Spirostomum ambiguum (Ehrenberg) major in solutions of different hydrogen ion concentration. The survival time is defined as the longest time for which the animals can remain in the solution of harmful hydrogen ion concentration and afterwards recover their normal appearance when transferred back to a solution, the hydrogen ion concentration of which is known to be harmless. 2. The results are given of experiments carried out in two solutions both of which provided media of known hydrogen ion concentration, but allowed this factor to be controlled by entirely different substances. The solutions were: (i) Palitzsch's borax-boric acid buffer mixture diluted ten times with glass distilled water. (ii) Cambridge tap-water (.0042 N carbonates) containing regulated amount of carbon dioxide in solution. 3. These experiments showed that the hydrogen ion concentration was a very important factor in determining the survival time of Spirostomumin the medium. $$$ media of pH 7.4 the Spirostomum survive indefinitely but in solutions of pH 9.4 they rapidly die after greater or less swelling, according to the osmotic pressure of the medium. The time of survival decreases with increasing alkalinity and between pH 9.0 and 7.6 it is inversely proportional to the hydrogen ion concentration. Between pH 7.6 and 7.4 the time of survival is not proportional to the hydrogen ion concentration and a very slight decrease in the hydrogen ion concentration at this point will cause a very considerable, and quite disproportionate, decrease in the time of survival. It is suggested that such a slight decrease in the hydrogen ion concentration of the water is the possible explanation of the very sudden disappearance of Spirostomum from ponds, where it was existing in very large numbers. The destruction of the Spirostomum in media of greater alkalinity than pH 7.4 is probably due to the increase in alkalinity affecting the body wall in such a way that it becomes more permeable to water, the result, as observed, being that the animals swell up and eventually burst.