essentially the same kind physiologically, or pathologically, as these
which can be and are occasionally produced in the individual soma by
mechanical stimulus and injury to the periosteum. The fact that a hormone
from the testis affects the development of the antler, as well as our
knowledge of hormones in general, suggests a special theory of the
heredity of somatic modifications due to external stimuli. Physiologists
are apt to look for a particular gland to produce every internal
secretion. But the fact that the wall of the intestine produces secretion,
which carried by the blood causes the pancreas to secrete, shows that a
particular gland is not necessary. There is nothing improbable in
supposing that a tissue stimulated to excessive growth by external
irritation would give off special substances to the blood. We know that
living tissues give off products, and that these are not merely pure CO2
and H2O, but complicated compounds. The theory proposed by me in 1908 was
that we have within the gonads numerous gametocytes whose chromosomes
contain factors corresponding to the different parts of the soma, and that
factors or determinants might be stimulated by products circulating in the
blood and derived from the parts of the soma corresponding to them. There
is no reason to suppose that an exostosis formed on the frontal bone as a
result of repeated mechanical stimulation due to the butting of stags
would give off a special hormone which was never formed in the body
before, but it would probably in its increased growth give off an
increased quantity of intermediate waste products of the same kind as the
tissues from which it arose gave off before. These products would act as a
hormone on the gametocytes, stimulating the factors which in the next
generation would control the development of the frontal bone and adjacent
tissues.

The difficulty of this theory is one which has occurred to biologists who
have previously made suggestions of a connexion between hormones and