From the enormous work which has been done on cancer with the microscope and the test tube, it would seem sometimes that research workers have become somewhat myopic, and not farsighted enough to recognize the true value of statistical studies and clinical observations. In these lectures we have attempted to make a brief synthetic study of some of the work which has been done in connection with cancer, and from this we believe that certain conclusions can be drawn; if these are correct and followed, it is hoped that much more can be accomplished in regard to the prophylaxis and cure of this more than threatening, fatal malady. In order that you may hold clearly the points which have been made I want to give you a synopsis or conclusions of them, as they have been brought out in this and preceding lectures. 1. Cancer is but a deviation from the normal life and action of certain of the ordinary cells of the body, which, for some as yet unexplained reason, take on an abnormal or morbid action; with this there is a continued tendency to a malignancy which invades contiguous tissue, and in the end tends to destroy life. 2. There is some reason to believe that this action first takes place in what are known as “embryonic rests,” or pre-natal, wrongly placed tissue elements, which, however, are now shown to exist in every one, in many localities: but the reason why they take on this malignant action, and form cancer, has not been satisfactorily explained. 3. Cancer is _not_ wholly due to traumatic causes, although those play a not inconsiderable part in its occurrence in certain localities and cases. 4. It is pretty conclusively decided that cancer is _not_ caused by a micro-organism, or parasite. 5. It is also known clinically and experimentally that it is _not_ contagious. 6. _Nor_ is it hereditary in any appreciable degree. 7. Occupation has _not_ any very great influence on the occurrence of cancer, although it is more frequent in some pursuits than in others. 8. Cancer is _not_ altogether a disease of older age, although its incidence is greatly increased with advancing years. 9. It does _not_ especially belong to or affect any particular sex, race, or class of persons. 10. It is _not_ confined to any location or section of the earth, but has been observed in all countries and climates. 11. No single cause of cancer has yet been demonstrated, nor is it likely that this will ever be the case, as the experimental and other investigations have covered almost every possible line of research, with only _negative_ results. 12. The exclusion of almost every other possible cause of cancer, as well as its pathological history, leads to deranged metabolism as the only remaining possible etiological element; this acts by inducing changes in nutrition, which latter depends on diet and the proper action of the secretory and excretory organs, which, still further, may be affected by nervous influences.