120 HERBERT SPENCER

the limited increase of size produced in any organ
by a limited increase of its function, is not maintained
unless the increase of function is permanent. When
the modifying influence is removed, the organism
rebounds or tends to rebound. A lasting change of
importance involves a re-organisation, a new state of
equilibrium.

On inductive and deductive grounds, Spencer
summed up in four conclusions :—

(1) An adaptive change of structure will soon reach

a point beyond which further adaptation will
be slow.

(2) When the modifying cause has been but for a

short time in action, the modification generated
will be evanescent.

(3) A modifying cause acting even for many genera-

tions will do little towards permanently alter-
ing the organic equilibrium of a race.

(4) On the cessation of such cause, its effects will

become unapparent in the course of a few
generations.

But two cautions must be emphasised (a) that
Spencer, in this discussion, dealt only with those
direct adjustments which are referable to the action
of use or disuse, or of surrounding influences; and
(b) that we have no security in regarding these as
being as such transmissible.

By adaptations biologists usually mean permanent
adjustments, and there are two theories of the origin
of these: (a) by the action of natural selection on
inborn variations, or (b) by the inheritance of the
directly acquired bodily modifications.

Cell-Life.—In this chapter, interpolated in thection is followed by extra growth, but that a