The lectures were prepared for and delivered to practicing physicians at the New York Skin and Cancer Hospital, in connection with the regular Wednesday lectures on Diseases of the Skin, as I felt that I should give them the benefit of what I felt to be of value in my own practice, private and public. Although holding the views here expressed for many years I have hesitated writing strongly on the subject before, lest I should be misunderstood or misjudged: for favorable results based solely on a clinical diagnosis of cancer are always doubted. I have also feared lest by advocating a dietetic and medical consideration and treatment of cancer, which possibly might not be carried out exactly, I might really do harm; since some might be led to neglect operative measures in proper cases, at the proper time; and so in certain instances great injury and injustice might be done to the patient, and the time pass in which a surgical operation might possibly be of service. But with my views and experience, strengthened greatly by what studies I have been able to make in the midst of a busy professional life, I now feel that I should do wrong in not presenting the results and conclusions of my study and observation. And I wish also to enter my strong protest against the course which is usually followed in regard to cancer, both before and after operation. With a rather extended experience during the last forty years, I have rarely if ever found a patient with cancer who has received adequate and continuous medical care before operation, with a view of discovering and rectifying the cause of the morbid growth. Too often when a cancer is suspected or discovered it is taken as a foregone conclusion that the malady is hopeless, except as the _results of the disease_, that is the new growth, may be removed by the knife, X-ray, radium, caustics, etc. And after a surgical operation, as far as my observation goes, the patients are invariably left entirely to their own resources, with the hope, alas, too often futile, that the tumor will not regrow, but with no attempt to so guide the life that there shall not be the same tendency to a recurrent malignant new-formation. Against this latter course I also raise my earnest protest. In presenting matter from literature bearing on the subject under discussion I am well aware that I have hardly more than touched the surface of the deep ocean of recorded observations on cancer, but it was the best that I could do in my busy life. I only hope that others will take up in earnest the subjects here presented, and that this pioneer work may lead to the building of a strong and permanent structure regarding the true basic cause of cancer. Truth never fears proof.