Page:Collected Physical Papers.djvu/333

Rh to choose specimens which exhibit little fatigue. Having obtained such a specimen I took records of responses for increasing stimuli caused by increasing amplitudes of vibration.

In the record given (fig. 88) the amplitude of vibration was increased from 2°.5 to 12°.5 by steps of 2°.5

(cauliflower-stalk). It will be noticed the remarkably definite manner in which the response increases with the stimulus. The rise is at first rapid, but with high intensities of stimulus there is a tendency for the response to approach a limit.

Additive effect.—There is apparently little or no response when the stimulus is feeble. But even a subminimal stimulus, though singly ineffective, becomes effective by the summation of several. This is shown in fig. 89, where the first record 𝑎 is the response to a