66 THE ENZYME TREATMENT OF CANCER
or less complete of the asexual generation, when robbed of its embryo, or when it fail to form such, can—and this is established—give origin to a malignant carcinomatous tumour, the nature of cancer is clear. The vagrant primary germ-cell is the seed, while its fruit, sometimes represented by an embryoma, may, on occasion, take the form of a carcinoma.
In the foregoing pages, written in 1902, cancer is spoken of as “a disease,” for not until the researches had advanced much farther did it become clear that cancer was a natural phenomenon. The origin of a cancer from “a vagrant germ-cell “ is urged; but on grounds, given later, it soon became necessary to restrict this power of independent development to some few only of the vagrant germ-cells. Its asexual nature is clearly defined in the foregoing, and while at that time its restriction to mammals seemed clear (although in 1895 its occurrence in some other vertebrates had been recorded, as I found later on), below the mammals it is still anything but common. Even now (1911) no case is known in reptiles, and but a few instances have been found in birds, while in many thousands of frogs examined the writer has only encountered one undoubted case of epithelioma. Considering its frequency in mammals, especially in man, the statement made above of its connection with uterine gestation would still appear to have a basis of fact underlying it. The adaptation of the asexual generation (trophoblast) to uterine life, shown by the occurrence of uterine gestation, favours its abnormal development in mammals as a parasitic cancer, as in no other class of back-boned animals. In the following chapter an attempt will be made to show how the tumours are related among themselves, and to the individual harbouring such a new formation.