versa. Delage, as seen above, does not consider that increase or decrease
of particular muscles can be inherited, but only the muscular system in
general. If, however, in consequence of the disuse of a group of muscles
there was a general diminution of the inherited muscular system, the
special group would remain diminished while the rest were developed by use
in the individual: there would thus be a heredity produced indirectly.
With regard to general conditions of life, Delage states that there are
only two of which we know anything--namely, climate and alimentation--and
he merely suggests that temperature and food act at the same time on the
cells of the body and on the similar substances in the egg.

H. M. Vernon (_Variation in Animals and Plants_, 1903, pp. 351 _seq._)
cites instances of the cumulative effects of changed conditions of life,
and points out that they are not really instances of the inheritance of
acquired characters, but merely of the germ-plasm and the body tissues
being simultaneously affected. He then asks, Through what agency is the
environment enabled to act on the germ-plasm? And answers that the only
conceivable one is a chemical influence through products of metabolism
and specific internal secretions. He cites several cases of specific
internal secretions, making one statement in particular which seems
unintelligible, viz. that extirpation of the total kidney substance of a
dog leads not to a diminished secretion of urine but to a largely
increased secretion accompanied by a rapid wasting away which soon ends
fatally.

Whenever a changed environment acts upon the organism, therefore, it to
some extent affects the normal excretions and secretions of some or all of
the various tissues, and these react not only on the tissues themselves,
but also to a less degree upon the determinants representing them in the
germ-plasm. Thus the relative size of the brain has decreased in the tame