Page:Collected Physical Papers.djvu/287

Rh is produced an equal and opposite response (fig. 64). If now both the ends A and B are stimulated simultaneously, the responsive electromotive variation at the two ends will continuously balance each other and the galvanometer spot will remain stationary. Fig. 65 gives the record of series of equal and opposite responses by alternate stimulation of A and B.

The similarities of response of inorganic and living substances are now sufficiently evident. We have to extend the inquiry to see whether this similarity extends to this point only, or goes still further. Are the response-curves of the inorganic modified by the influence of external agencies, as the living responses are found to be?

It has been said that under rapidly succeeding stimuli, the intermittent effects of single shocks become fused, and the muscle responds by an almost unbroken tetanic curve (fig. 66). If the frequency is not sufficiently great, there is an incomplete tetanus and the response-curve becomes jagged.

The very same thing occurs in metals. I subject the wire to quickly succeeding vibrations. The curve rises