ASPECTS AND ETIOLOGY OF CARCINOMA 53
established by pathological research, such as those given in tile latest edition of Ziegler’s “Pathologic,” will be taken for granted. It will be assumed that at the basis there is morphologically but one form of cancer, no matter how different it may appear to be in diverse localities.
A cancer of the skin is naturally different from one of the uterus or liver, for it grows and increases under other conditions. Ziegler, for one, adduces reasons against the supposed origin of cancer from some effects of unicellular organisms, and to his objections something more can be added. It is not in the nature of parasitic maladies to lead to cellular increase, such as is characteristic of cancer; and, while the phenomena of destruction possibly present themselves prominently to the surgeon and the pathologist, those of indefinite unrestricted cellular increase and multiplication most impress the embryologist. And if the nature of cancer to be brought out in the course of the following be the true one, any further one is a superfluity.
The conclusions are based chiefly, but not entirely, upon researches in Elasmobranch fishes,* and to any but vertebrate embryologists there might appear to be no warrant for applying results obtained in animals so low down in the scale to man himself. But the broad outlines, the laws, and even most of the details of the development, are the same in man as in the fishes, and the life-cycle of the former can be interpreted in terms of that of the latter. The starting-point goes back more than two years to the beginning of researches upon the germ-cells, and with these to the earlier work of Wilms upon tile embryomata. The results of the work, and of previous necessary
*Also upon researches in mammalian development, especially upon the trophoblast (larva or phorozoon, asexual generation), allantoic placenta, critical period, and span of gestation.