t the whole range of response phenomena a parallelism between
animal and vegetable could be detected. That is to say, I desired to
know, with regard to plants, what was the relation between intensity of
stimulus and the corresponding response; what were the effects of
superposition of stimuli; whether fatigue was present, and in what
manner it influenced response; what were the effects of extremes of
temperature on the response; and, lastly, if chemical reagents could
exercise any influence in the modification of plant response, as
stimulating, anaesthetic, and poisonous drugs have been found to do with
nerve and muscle.

If it could be proved that the electric response served as a faithful
index of the physiological activity of plants, it would then be possible
successfully to attack many problems in plant physiology, the solution
of which at present offers many experimental difficulties.

With animal tissues, experiments have to be carried on under many great
and unavoidable difficulties. The isolated tissue, for example, is
subject to unknown changes inseparable from the rapid approach of death.
Plants, however, offer a great advantage in this respect, for they
maintain their vitality unimpaired during a very great length of time.

In animal tissues, again, the vital conditions themselves are highly
complex. Those essential factors which modify response can, therefore,
be better determined under the simpler conditions which obtain in
vegetable life.

In the succeeding chapters it will be shown that the response phenomena
are exhibited not only by plants but by inorganic substances as well,
and that the responses are modified by various conditions in exactly
the same manner as those of animal tissues. In order to show how
striking are these similarities, I shall for comparison place side by
side the responses of animal tissues and those I have obtained with
plants and inorganic substances. For the electric response in animal
tissues, I shall take the latest and most complete examples from the
records made by Dr. Waller.

But before we can obtain satisfactory and conclusive results regarding
plant response, many experimental difficulties will have to be
surmounted. I shall now describe how this has been accomplished.[7]

FOOTNOTES:

[2] In some physiological text-books much wrong inference has been made,
based on the supposition that the injured end is zinc-like.

[3] 'The exciting cause is able to produce a p