APPENDIX B 253
every normal human gestation developed a conspicuous destroying and eroding tendency—that for the purpose of the implantation of the egg it destroyed the decidua, and that processes of it might extend almost through the thickness of the uterus. Between this normal destruction and that of malignant chorio-epithelioma a completely closed chain of cases could without difficulty be found, with gradual progression of malignancy. Cases often arose where it was difficult for the pathologist to determine whether he was dealing with a normal or an abnormal destruction.
If a parasite were postulated to account for chorioepithelioma, its advocates would find difficulty in escaping from the conclusion that such a parasite was not also required to stimulate the implantation and development of the normal egg. He decided that malignant chorioepithelioma only differed in degree from the normal processes. Certain embryomata or teratomata were encountered in the sexual organs, ovaries and testes. Occasionally these tumours were very malignant. They destroyed, recurred, and formed metastases in distant organs. In recent years trophoblast or chorion-cells had been found associated with these turnouts. This trophoblastic tissue in its typical form was completely characteristic, and it resembled in every morphological respect the trophoblast of normal gestation. At times the cells formed solid epithelial strings and nests—there arose ordinary carcinoma. In this connection he produced micro-photographs taken from such a tumour of the testis. It consisted chiefly of nothing but trophoblastic tissue, with here and there cartilage, skin, and tubes of columnar epithelium—a picture which, he maintained, each of his hearers would recognize as the trivial picture of a carcinoma or adenoma. He desired that day to add something new which appeared to him to show that chorio-epithelioma was not limited to the sexual organs, but that it might occur elsewhere. In itself that would not be specially remarkable, because in