The preventive treatment of old age is in no less degree possible than that of any other disease. To prevent old age rationally, we must avoid all those harmful agencies which may be deleterious to the glands with internal secretions, as it is the degeneration of these glands that brings it about. These agencies, however, being exceedingly numerous, we have mentioned in the previous chapter only those which are in the highest degree detrimental and also the most frequent. By avoiding these we believe we could successfully combat old age, but only for a certain time; and if not longer, in spite of our careful hygiene, it would not be our fault, but that of our ancestors of many generations ago who did not observe the rules of hygiene even as well as we do, and left us ductless glands of inferior quality. Parents can only bequeath to their children ductless glands of the same quality as they themselves possess. This undoubted fact is clearly proved by the experimental, pathological, and anatomical results we have mentioned in the chapter on heredity. We will illustrate this by the following examples, which will show how often it is difficult to avoid harmful agencies, and how much depends on having been born with healthy ductless glands. A person inhales air that contains virulent bacilli and contracts tuberculosis. Another drinks a glass of water or milk, contaminated by water or kept in vessels that have been washed with water containing the bacilli of Eberth, and contracts typhoid fever. Conversely, others who have inhaled the same air and drunk much more of the same water, have remained free from any infection. The cause of this is that the first mentioned have inherited defective ductless glands from their ancestors, and probably afterward have ill-treated these glands by an immoderate use of all those agencies that are detrimental to them, such as alcohol, sexual excesses, much meat, tobacco, tea and coffee in large quantities, etc., and thus could not produce anti-bodies to counteract the infection. Of course, the fault does not lie entirely with such people, but that from their birth they are the victims of the immoderation of their ancestors; and by this fact alone are doomed to more easily succumb in the incessant fight against the microbes, and therefore a limited lifetime has been already meted out to them at birth. We have, in the chapter on heredity, quoted instances of persons coming of short-lived families, who reached a great old age; but this was due solely to exceedingly careful hygiene. It is not always easy to observe these rules scrupulously, and besides often necessitates the possession of means to carry them out and to enable us to be more exempt from the wear and tear of life—cares and sorrow,—which shorten the lives even of persons with healthy glands, though much more of persons who have inherited defective ductless glands.