Page:Collected Physical Papers.djvu/276

256 Medium stimulus, slow intermittence.—In this set of experiments, the radiator was moved further away so that the intensity of the stimulus was moderate; the successive flashes of radiation were applied at intervals of two seconds. These moderate excitations are found to be summated and when in slow succession, the effect of each shock can be distinguished as the steps in the ascending curve, as in fig. 60 (a).

Rapid intermittence.—When the stimuli follow each other with great rapidity, the intermittent effects are fused together; the rising curve is found to be unbroken and the effect may be described as 'tetanic' as in fig. 60 (b).

The response curves of muscles under the above conditions are similar to the above.

The response of many inorganic receivers was found to exhibit the peculiarity that while moderate intensity of stimulus produced the normal response of a given sign, a feeble stimulus elicited the opposite reaction, the sign of response being reversed (cf. p. 137). I succeeded later in demonstrating the occurrence of similar