Fig. 116.—Modified Abnormal Response in (A) Nerve and (M) Metal converted into Normal, after Continuous Stimulation
(A) is the record for nerve (recording galvanometer not being dead-beat shows after-oscillation); the abnormal ‘up’ is converted into normal ‘down’ after continuous stimulation. (M) is the record for metal, the abnormal ‘down’ being converted into normal ‘up’ after like stimulation.
But these modified responses usually become normal when the specimen is subjected to stimulation either strong or long continued ([fig. 116]).
Diphasic variation.—A diphasic variation is observed in nerve, if the wave of molecular disturbance does not reach the two contacts at the same moment, or if the rate of excitation is not the same at the two points. A similar diphasic variation is also observed in the responses of plants and metals ([figs. 26], [68]).
Effect of temperature.—In animal tissues response becomes feeble at low temperatures. At an optimum temperature it reaches its greatest amplitude, and, again, beyond a maximum temperature it is very much reduced.
We have observed the same phenomena in plants. In metals too, at high temperatures, the response is very much diminished ([figs. 38], [65]).
Effect of chemical reagents.—Finally, just as the response of animal tissue is exalted by stimulants, lowered by depressants, and abolished by poisons, so also we have found the response in plants and metals undergoing similar exaltation, depression, or abolition.
We have seen that the criterion by which vital response is differentiated is its abolition by the action of certain reagents—the so-called poisons. We find, however, that ‘poisons’ also abolish the responses in plants and metals ([fig. 117]). Just as animal tissues pass from a state of responsiveness while living to a state of irresponsiveness when killed by poisons, so also we find metals transformed from a responsive to an irresponsive condition by the action of similar ‘poisonous’ reagents.