which constantly demands
blood, produces waste matter, secretes, or absorbs--then all the other
active organs become implicated in the change. The functions performed
by them have to constitute a moving equilibrium; and the function of one
cannot, by alteration of the structure performing it, be modified in
degree or kind, without modifying the functions of the rest--some
appreciably and others inappreciably, according to the directness or
indirectness of their relations. Of such inter-dependent changes, the
normal ones are naturally inconspicuous; but those which are partially
or completely abnormal, sufficiently carry home the general truth. Thus,
unusual cerebral excitement affects the excretion through the kidneys in
quantity or quality or both. Strong emotions of disagreeable kinds check
or arrest the flow of bile. A considerable obstacle to the circulation
offered by some important structure in a diseased or disordered state,
throwing more strain upon the heart, causes hypertrophy of its muscular
walls; and this change which is, so far as concerns the primary evil, a
remedial one, often entails mischiefs in other organs. "Apoplexy and
palsy, in a scarcely credible number of cases, are directly dependent on
hypertrophic enlargement of the heart." And in other cases, asthma,
dropsy, and epilepsy are caused. Now if a result of this
inter-dependence as seen in the individual organism, is that a local
modification of one part produces, by changing their functions,
correlative modifications of other parts, then the question here to be
put is--Are these correlative modifications, when of a kind falling
within normal limits, inheritable or not. If they are inheritable, then
the fact stated by Mr. Darwin that "when one part is modified through
continued selection," "other parts of the organization will be
unavoidably modified" is perfectly intelligible: these entailed
secondary modifications are transmitted _pari passu_ with the successive
modifications produced by selection. But what if they are not
inheritable? Then these secondary modifications caused in the
individual, not being transmitted to descendants, the descendants must
commence life with organizations out of balance, and with each increment
of change in the part affected by selection, their organizations must
get more out of balance--must have a larger and larger amounts of
re-organization to be made during their lives. Hence the constitution of
the variety mus