The two response-curves seen in the accompanying diagram (fig. 5), and taken from the same muscle by the two methods simultaneously, clearly exhibit this. Thus we see that electrical response can not only take the place 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.