As to the heredity of cancer, all that can be said is that the burden of proof rests upon those who assert it. It is really curious how widespread the belief is that cancer "runs in families," and how exceedingly slender is the basis of evidence for such a belief. There are so many things that we do not know about cancer that any positive statement of any kind would be unbecoming. It would be absurd to declare that a disease, of which the cause is still unknown, either is or is not inherited. And this is our position in regard to cancer. An overwhelming majority of the evidence so far indicates that it is not a parasite; if it were, of course, we could say positively that it is not inherited. Although we are getting a discouraging degree of familiarity with the process and clearly recognize that it consists chiefly in the sudden revolt or rebellion of some group of cells, a tendency which quite conceivably might be transmitted to future generations, yet it is highly improbable, on both biological and pathological grounds, that such is the case. If this rebellious tendency were transmitted we should at least have the right to expect that it would appear in the cells of the same organ or region of the body. It is a singular fact that in all the hundreds of cases in which cancer has appeared in the child of a cancerous parent it has almost invariably appeared in some different organ from that affected in the parent. For instance, cancer of the lip in the father may be followed by cancer of the liver in the son or daughter, while cancer of the breast in the mother will be followed by cancer of the lip in a son. Further than this, the percentage of instances in which cancer appears in more than one member of a family is decidedly small, considering the frequency of the disease. I took occasion to look into the matter carefully from a statistical point of view some ten or twelve years ago, and out of a collection of some fifty thousand cases of cancer less than six per cent were found to give any history of cancer in the family. And this, of course, simply means that some one of the relatives of the patient had at one time developed the disease. In fact, the consensus of intelligent expert opinion upon the subject of heredity of cancer is, that though it may occur, we have comparatively little proof of the fact; that the percentage of cases in which there is cancer in the family is but little larger than might be expected on the doctrine of probabilities from the average distribution. Though possibly the offspring of a cancerous individual may display a slightly greater tendency toward the development of that strange, curious process of "autonomy" than the offspring of the average individual, this tendency is so small and occurs so infrequently as to be a factor of small practical importance in the propagation and spread of the disease.