When I place a drop of Paramecium culture on a slide having on two sides parallel pieces of baked clay which serve as electrodes and allow a constant current of about .2 milliampère to flow through, it will be seen that the infusoria at room temperature move toward the negative pole at a rate averaging 1–1.4 mm. per second. (Figure 39.) If I increase the temperature, the rate of movement is increased. Here the galvanic and the thermal stimuli influence each other in such a manner that the reaction to the galvanic is increased by the thermal stimulation. This summation of excitation is readily understood on the basis of the laws concerning the effect of temperature upon the velocity of chemical change established by _van’t Hoff_. If, however, the Paramecia are in a 1 per cent. alcoholic solution, then, as was shown by _Nagai_,[164] the rapidity of movement following galvanic stimulation is decidedly reduced. The interference effect between the galvanic and chemical stimulation is, because of the depressing effect of the latter, likewise readily understood. [164] _Nagai_: “Der Einfluss verschiedener Narcotica, Gase and Salze auf die Schwimmgeschwindigkeit von Paramæcium.” Zeitschr. f. allgem. Physiologie Bd. VI, 1907. [Illustration: Fig. 40. Thigmotaxis of Paramaecium aurelia. (After _Jennings_.)] Greater difficulty meets us, however, in the following instance. The forward movements of the Paramecia follow in consequence of the fact that the individual cilia of the body lash more powerfully backward than forward. If now the Paramecia, while moving forward, meet with a resisting body, they withdraw sideways while executing a sudden strong forward ciliary stroke. The strong mechanical stimulation brings about retraction of the organism. Entirely different are the results when the impact is weak. If Paramecia while slowly swimming touch a resisting object with the anterior portion of the body, withdrawal does not occur. The infusoria remain under proper conditions in contact with the resistance, and the rhythmic activity of the cilia directly against resistance, as well as those on the other side toward the posterior portion of the body, are more or less inhibited. (Figure 40.) The degree of inhibition brought about by this weak mechanical stimulation may vary considerably. At times the cilia of the whole body suddenly cease their movement. (Figure 41, A.) At other times, this cessation is limited to the cilia in the anterior portion of the body (Figure 41, B), while the movements of those on the posterior portion of the body are of less amplitude or are irregular and weak. In all cases the infusorium remains quiescent in the water in contact with the resistance, and it is not uncommon to find numerous individuals in apposition with particles of ground, slimy detritus, plant fibers and so forth. (Figure 41, C.) In short, the rhythmic activity of the cilia of the Paramecia receiving their normal impulses of excitation from the