He began an examination of inorganic matter in the same way as a
biologist examines a muscle or a nerve. He subjected metals to various
kinds of stimulus--mechanical, thermal, chemical, and electrical. He
found that all sorts of stimulus produce an excitatory change in them.
And this excitation sometimes expresses itself in a visible change of
form and sometimes not; but the disturbance produced by the stimulus
always exhibits itself in an _electric response_. He next subjected
plants and animal tissues to various kinds of stimulus and also found
that they also give an _electric response_. Finding that a universal
reaction brought together metals, plants and animals under a common law,
he next proceeded to a study of _modifications in response_, which occur
under various conditions. He found that they are all benumbed by cold,
intoxicated by alcohol, wearied by excessive work, stupified by
anaesthetics, excited by electric currents, stung by physical blows and
killed by poison--they all exhibit essentially the same phenomena of
fatigue and depression, together with possibilities of recovery and of
exaltation, yet also that of permanent irresponsiveness which is
associated with death--they all are responsive or irresponsive under the
same conditions and in the same manner. The investigations showed that,
in the entire range of response phenomena (inclusive as that is of
metals, plants and animals) there is no breach of continuity; that "the
living response in all its diverse modifications is only a repetition of
responses seen in the inorganic" and that the phenomena of response "are
determined, not by the play of an unknowable and arbitrary _vital
force_, but by the working of laws that know no change, acting equally
and uniformly throughout the organic and inorganic matter."[14]