ce of the mechanical record, but has the further advantage of being
applicable in cases where the latter cannot be used.

#Electrical response: A measure of physiological activity.#--These
electrical changes are regarded as physiological, or characteristic of
living tissue, for any conditions which enhance physiological activity
also, _pari passu_, increase their intensity. Again, when the tissue is
killed by poison, electrical response disappears, the tissue passing
into an irresponsive condition. Anaesthetics, like chloroform, gradually
diminish, and finally altogether abolish, electrical response.

[Illustration: FIG. 5.--SIMULTANEOUS RECORD OF THE MECHANICAL (M) AND
(E) ELECTRICAL RESPONSES OF THE MUSCLE OF FROG. (WALLER.)]

From these observed facts--that living tissue gives response while a
tissue that has been killed does not--it is concluded that the
phenomenon of response is peculiar to living organisms.[5] The response
phenomena that we have been studying are therefore considered as due to
some unknown, super-physical 'vital' force and are thus relegated to a
region beyond physical inquiry.

It may, however, be that this limitation is not justified, and surely,
at least until we have explored the whole range of physical action, it
cannot be asserted definitely that a particular class of phenomena is by
its very nature outside that category.

#Electric response in plants.#--But before we proceed to the inquiry as to
whether these responses are or are not due to some physical property of
matter, and are to be met with even in inorganic substances, it will
perhaps be advisable to see whether they are not paralleled by phenomena
in the transitional world of plants. We shall thus pass from a study of
response in highly complex animal tissues to those given under simpler
vital conditions.

Electric response has been found by Munck, Burdon-Sanderson, and others
to occur in sensitive plants. But it would be interesting to know
whether these responses were confined to plants which exhibit such
remarkable mechanical movements, and whether they could not also be
obtained from ordinary plants where visible movements are completely
absent. In this connection, Kunkel observed electrical changes in
association with the injury or flexion of stems of ordinary plants.[6]
My own attempt, however, was directed, not towards the obtaining of a
mere qualitative response, but rather to the determination of whether
throughou