al
mechanical forces, adapted in amounts and directions to balance or
outbalance certain external ones. The recognition of an object is
impossible without a harmony between the changes constituting perception
and particular properties coexisting in the environment. Escape from
enemies supposes motions within the organism related in kind and
rapidity to motions without it. Destruction of prey requires a
particular combination of subjective actions, fitted in degree and
succession to overcome a group of objective ones.

The difference of this correspondence in inanimate and animate bodies
may be expressed by symbols. Let A be a change in the environment; and B
some resulting change in an inorganic mass. Then A having produced B,
the action ceases. But take a sufficiently organised living body, and
let the change A impress on it some change C; then, while the
environment A is occasioning _a_, in the living body, C will be
occasioning _c_: of which _a_ and _c_ will show a certain concord in
time, place, or intensity. And while it is in the continuous production
of such concords or correspondences that life consists, it is _by_ the
continuous production of them that life is maintained.

As, in all cases, we may consider the external phenomena as simply in
relation, and the internal phenomena also as simply in relation, the
broadest and most complete definition of life will be:--_the continuous
adjustment of internal relations to external relations_. It will be
best, however, commonly to employ its more concrete equivalent--to
consider the internal relations as "definite combinations of
simultaneous and successive changes"; the external relations as
"coexistences and sequences," and the connection between them as a
"correspondence."

_The Degree of Life Varies as the Degree of Correspondence_

It is now to be remarked that the life is high in proportion as this
correspondence between internal and external relations is
well-fulfilled.

Each step upward must consist in adding to the previously adjusted
relations which the organism exhibits some further relation, parallel to
a further relation in the environment. And the greater correspondence
thus established must, other things being equal, show itself both in
greater complexity of life and greater length of life--a truth which
will be duly realised on remembering the enormous mortality which
prevails among lowly-organized creatures, and the gradual increase of
longevi