Regarding, then, cancer as a systemic disease, of which the tumor is but a local expression, often or perhaps always the result of local injury or irritation, possibly of one or more “embryonic rests,” let us briefly review the evidence in support of this view, and the measures found successful in combating the basic cause of the disease.
First let me remind you of the _negative_ and _positive_ results of laboratory and other study, which are pretty well conceded by those who know most about the disease; and in presenting these I cannot do better than to quote what I have collected in a former article.[4] There are eight of these in each group.
1. Clinically and experimentally cancer is shown to be _not_ contagious or infectious; although under just the right conditions certain malignant new growths can be inoculated in some animals of the same species, but not in other species, and human cancer cannot be transplanted on animals.
2. Although microörganisms of many kinds often have been found and claimed as the cause of cancer, there has been no concurrence of opinion in regard to them, and it is now pretty conclusively agreed that cancer is _not_ caused by a microörganism or parasite.
3. Cancer is _not_ wholly a result of traumatism; although local injury may have much to do with its development in some particular locality, even as in connection with the late lesions of syphilis.
4. Cancer is _not_ hereditary in any appreciable degree; although some tendency in that direction has been demonstrated in certain strains of mice.
5. Occupation has _not_ any very great influence on the occurrence of cancer; although it is more frequent in some pursuits than in others.
6. Cancer is _not_ altogether a disease of older years; although its occurrence is decidedly influenced by advancing age.
7. It does _not_ especially belong to or affect any particular sex, race, or class of persons.
8. Cancer is _not_ confined to any location or section of the earth, but has been observed in all countries and climates.
But while laboratory and other investigations have not demonstrated any single cause of cancer and have yielded only negative results, they have, by elimination, cleared the way for a study of its cause along other lines, which are bright with promise. They have also established certain facts which confirm the views which from time to time have been briefly expressed by many who were best acquainted with cancer; namely, that, because of its constant recurrence, and from the failure of surgery to check its rising mortality, it must be of a constitutional nature, intimately associated with dietary or nutritional elements, as I have elsewhere shown.[5]