THE CANCER PROBLEM 111
of an embryo would stay its growth just as the formation of the sexual generation ends the growth of a shoot of a flowering plant. How does “the embryo” bring about this result? It does not devour the trophoblast, but it must produce something which, as was pointed out two years ago,* brings the degeneration to pass. Only in ordinary chorio-epithelioma is the malignant neoplasm a persisting portion and derivative of the trophoblast of the immediately previous gestation. Any ordinary cancer or sarcoma is a new development of trophoblast, due to the attempt of a germ-cell to start the cycle anew. Except in mode of nutrition, this irresponsible trophoblast does not resemble normal trophoblast, but it often mimics the structure in which it lies or it is like no other organ or tissue in the body. In any and every higher mammalian (Eutherian) development there is the potentiality of a malignant tumour,** chorio-epithelioma, and this danger exists until the degeneration of the trophoblast is an assured but not completed fact. As researches made some years ago, but never published, demonstrated,
* The Lancet, June 21, 1902, p. 1758.
** So far as is at present known, chorio-epithelioma does not occur in any mammal except man. The multiplicity of embryos in most other cases is against its happening. In almost every gestation in the pig, and often in the rabbit, there are abortive embryos, from the trophoblast of which a malignant tumour might arise but for the presence and influence of the other embryos. In the course of the discussion the case of a full-time anencephalic (headless) human foetus was cited as against the validity of the conclusions advanced. In this the entire alimentary canal and pancreas were absent. A little cross-examination elicited the information that nothing was known as to its foetal membranes, and that it was one of twins. The latter point is decisive in explaining how this monster had escaped the weeding-out of the critical period. Had it been a single embryo, not a twin, it would undoubtedly have been aborted at the critical period, and, moreover, hydatid mole or chorio-epithelioma would very possibly have followed.