esponse in a modified
tissue, they were strictly correspondent to similar phenomena in animal
tissues. The remaining test, of the influence of chemical reagents,
having now been applied, a complete parallelism may be held to have been
established between plant response on the one hand, and that of animal
tissue on the other.

[Illustration: FIG. 49.--NEARLY COMPLETE ABOLITION OF RESPONSE BY
STRONG KOH
The two vertical lines are galvanometer deflections due to .1 volt,
before and after the application of reagent. It will be noticed that
the total resistance remains unchanged.]

CHAPTER X

RESPONSE IN METALS

Is response found in inorganic substances?--Experiment on tin, block
method--Anomalies of existing terminology--Response by method of
depression--Response by method of exaltation.

We have now seen that the electrical sign of life is not confined to
animals, but is also found in plants. And we have seen how electrical
response serves as an index to the vital activity of the plant, how with
the arrest of this vital activity electrical response is also arrested
temporarily, as in the case amongst others of anaesthetic action, and
permanently, for instance under the action of poisons. Thus living
tissues--both animal and vegetable--may pass from a responsive to an
irresponsive condition, from which latter there may or may not be
subsequent revival.

Hitherto, as already said, electrical response in animals has been
regarded as a purely physiological phenomenon. We have proved by various
tests that response in plants is of the same character. And we have seen
that by physiological phenomena are generally understood those of which
no physical explanation can be offered, they being supposed to be due to
the play of some unknown vital force existing in living substances and
giving rise to electric response to stimulation as one of its
manifestations.

#Is response found in inorganic substances?#[14]--It is now for us,
however, to examine into the alleged super-physical character of these
phenomena by stimulating inorganic substances and discovering whether
they do or do not give rise to the same electrical mode of response
which was supposed to be the special characteristic of living
substances. _We shall use the same apparatus and the same mode of
stimulation as those employed in obtaining plant response, merely
substituting, for the stalk of a plant, a metallic wire, say 'tin'_
(fig.