THE EMBRYOLOGY AND ETIOLOGY OF TUMOURS 75
with
the remaining complicated” three-layered” tumours, which, as due to
developmental abnormalities of a single embryo, are stated to be monogerminal.
As, according to Wilms, all possible transitions between the most complicated
embryomata and the simpler tumours exist, there would appear to be no grounds
for this and similar increases in the hypotheses.
Apart
from its entirely hypothetical character, its lack of support in facts of embryology,
and its continual and unnecessary multiplication of causes, the theory of germ-shuntings
labours under other difficulties. It is not easy to conceive any adequate cause
for such shuntings during development, and the difficulty is greatly increased
when cases of multiple tumours in very different parts of the body, each of
which requiring one or more shuntings at some period or other, are taken
account of; for with them a normal development would appear to be quite out of
question. But, granted the possibility of such shuntings, the real difficulties
begin. What causes such a shunted germ, ignoring all laws of differentiation,
to embark upon a career of damage, riot, and destruction of its own? To take an
instance from Wilms, typical of many such: the germ of an osteo-sarcoma will be
a cell or germ of the periosteum of some bone. Normally, like its fellows, it
ought to have contributed to the formation of that bone. Instead, thereof, at
some period or other, after lying dormant, it breaks all bounds, and proceeds
on a line of development of its own. This is such that, unless brought to a
stop by some extrinsic cause or other (operation or death of the host), it may
be the parent-cell of more progeny than all the other bone-producing cells in
the body! In fine, Wilms ascribes to his shunted germs far greater
embryological potentialities than Nature ever endowed them with. On the other