3. Cancer is not wholly due to traumatic causes; although these may 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 microörganism or parasite; although various forms of these have been found in connection with the disease, and each has been claimed as the cause of cancer.
5. It is known clinically and experimentally that cancer is not contagious.
6. Nor is it hereditary in any appreciable degree; although certain rare instances have been reported in which such seems to be the case, and though some tendency in that direction has been demonstrated in certain strains of mice.
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 years; although its incidence is greatly increased with advancing age.
9. Cancer does not especially belong to or affect any particular sex, race, or class of persons. It is, however, more frequent in females than in males, although of late years the proportion in the latter is steadily rising.
10. Cancer is not confined to any climate, location, or section of the earth, but has been observed in all countries and climates, though with different frequency.
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.