11. _No_ single cause of cancer has yet been demonstrated; nor is it likely that this will ever be the case, as 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 and biochemical studies, all lead, therefore, to deranged metabolism as the only remaining possible etiological element. This latter acts by inducing changes in nutrition, and these in turn depend on diet and the proper or improper action of the secretory and excretory organs; these latter may, still further, be affected by nervous influences. 13. While the biochemistry of cancer does not as yet throw very great light on its true nature and cause, enough has been determined to show that the morbid changes in the cells are largely associated with deranged metabolism. 14. The blood in advancing cancer manifests changes which indicate vital alterations in the action of the organs which form blood and control the nutrition of the body and its cells. 15. Clinical and experimental evidence demonstrate that the secretions and excretions of the body exhibit departures from normal; these, while not wholly pathognomonic of cancer, still indicate metabolic disturbances which involve the nutrition of the cellular elements, and these disturbances are of importance. 16. The evidence seems certain that the cancer mass, when fully developed, secretes a hormone or poison which tends to augment its own growth, and hastens the lethal progress of the disease. 17. The mortality from cancer is undoubtedly on the increase in every portion of the globe, in spite of the assiduous activity of the laboratories and the immense advances in surgical procedure. 18. This increase in mortality is seen to vary inversely, and in about the same proportion, with the steadily diminishing mortality of tuberculosis, under recent careful medical guidance. 19. The increase of cancer mortality is found to follow closely along the lines of modern civilization. 20. The extension of cancer appears to depend largely upon the altered conditions of modern life, particularly along the lines of self-indulgence in eating and drinking, and indolence. 21. The augmentation in the consumption of meat, coffee, and alcoholic beverages in civilized communities is seen to be coincident with the great and proportionately greater augmentation of the mortality from cancer. 22. The nerve strain of modern life seems to be an element of importance, both through disturbance of metabolism and by direct action on morbidly deranged cells.