Response in the Living and Non-Living

by Jagadis Chandra Bose

(a) Arrangement for applying a short-lived E.M.F.
(b) Difference in the periods of recovery: (1) from instantaneous E.M.F.; and (2) that caused by mechanical stimulus.

The record was then taken as follows. The recording drum had a fast speed of six inches in a minute, one of the small subdivisions representing a second. The battery contact in the main potentiometer circuit was made for a quarter of a second as just mentioned and a record taken of the effect of a short-lived E.M.F. on the circuit containing the cell. (2) A record was next taken of the E.M. variation produced in the cell by a single stimulus. It will be seen on comparison of the two records that the maximum effect took place relatively later in the case of mechanical stimulus, and that whereas the galvanometer recovery in the former case took place in 11 seconds, the recovery in the latter was not complete till after 60 seconds ([fig. 60], b). This shows that it takes some time for the effect of stimulus to attain its maximum, and that the effect does not disappear till after the lapse of a certain interval. The time of recovery from strain depends on the intensity of stimulus. It takes a longer time to recover from a stronger stimulus. But, other things being equal, successive recovery periods from successive stimulations of equal intensity are, generally speaking, the same.

We may now study the influence of any change in external conditions by observing the modifications it produces in the normal curve.

Fig. 61.—Prolongation of Period of Recovery after Overstrain

Recovery is complete in 60″ when the stimulus is due to 20° vibration. But with stronger stimulus of 40° vibration, the period of recovery is prolonged to 90″.

Prolongation of period of recovery by overstrain.—The pair of records given in [fig. 61] shows how recovery is delayed, as the effect of overstrain. Curve (a) is for a single stimulus due to a vibration of amplitude 20°, and curve (b) for a stimulus of 40° amplitude of vibration. It will be noticed how relatively prolonged is the recovery in the latter case.