THE CANCER PROBLEM 113
growth of which was favoured by the absence of an “embryo” or sexual generation.
At that time there appeared to be one hopeful outlook for cancer research along the lines of embryology. It was that in every normal development the trophoblast, which in the absence of a completed embryo might become a malignant tumour, chorio-epithelioma, was invariably suppressed and degenerated. The task was to find out how this came about; for there appeared to be good reason for the hope, if not for the sure belief, that the factor or factors which brought about this result in normal development might also be potent when directed against an irresponsible trophoblast or cancer. To find these factors would be the solution of a general scientific problem of which, apparently cancer was but a special case. These factors have now been found, and in consequence cancer ceases to be a problem for the embryologist. A scientific solution of a certain problem has been obtained; whether or not this be at the same time a solution of the cancer problem in its medical aspects would not be for the embryologist to predict. He can only guarantee the truth of the embryological findings and conclusions, and maintain that these would remain, even though they should fail utterly when applied in the treatment of malignant tumours.
The change in nutrition initiated at the critical period in vertebrate animals, from fishes to man, is based in the commencing functional activities of the pancreatic gland or sweetbread. This introduces an alkaline digestion by means of the pancreatic juice with its various ferments. But what of the pre-critical nutrition ? There are many ways in which this might be investigated. One might examine normal trophoblast, cancer or sarcoma, blastoderm of a fish—such as the skate—cleaved eggs of an amphibian, or