Studies of Tolerance of Several Kinds of Animals to Heat, Electroshock, Hydrogen and Hydroxyl Ions.　-Ⅳ. Studies of tolerance of paramecium caudatum to hydrogen and hydroxyl ions.-

1. Tolerance of Paramecium Caudatumto hydrogen and hydroxyl ions I. E. PH change of environmental culture fluid was examined by means of microscopic observation. 2. Formulas are presented to express approximetely the tolerance (per cent probability of cessation response of ciliary motion) of paramecia in terms of time of exposure and concentration of hydrogen and hydroxyl ions. 3. The avobe formulas were able to be constructed by applying Chung's general formulas concerning stress and response.