THE INTERLUDE OF CANCER 133
ologist. They recall to him other similar phenomena in embryology. Reductions in numbers of units (cells), formerly of importance, but which now persist, not because they are really required, but because their existence and persistence are parts of an old scheme of the cycle of animal life.
The writer has had abundant opportunities of noting the liability of identical twins to cancer, but to state the matter in this way is misleading. Those individuals who develop malignant growths are as liable to such as are identical twins, and for the same reasons. Without doubt cancer is hereditary. This is abundantly borne out by clinical histories in my possession. There are records where both parents died of it, where even one or other grandparent developed cancer, and it is only too commonly told the writer that in some particular case the father or the mother was a victim of cancer. The most remarkable example known to me at present is in the family of a master-carpenter in Edinburgh. His mother died of uterine cancer, and he has lost all his brothers and sisters, seven in number, by some form or other of malignant disease. Embryologically regarded, persons suffer from cancer because they are at the basis members of a group of identical twins or triplets. It is, therefore, not from any and every aberrant germ-cell that a cancer takes its start, but from one or other of some few germ-cells, embryonic in destiny, cells which should have given rise to twins, triplets, etc., identical with the embryo, which arose in any particular gestation.
(continued from p 132) But if the number of young here arising at every gestation were much reduced, while all the preliminaries were retained, what a rich harvest of tumours might be the result! In a case of identical triplets, cited by Professor H. H. Wilder, at least two of the sisters died of cancer.