I. I shall mention the circumstances which favour the attainment of longevity.
II. I shall mention the phenomena of body and mind which attend it; and,
III. I shall enumerate its peculiar diseases, and the remedies which are most proper to remove, or moderate them.
I. The circumstances which favour longevity, are,
1. Descent from long-lived ancestors. I have not found a single instance of a person, who has lived to be 80 years old, in whom this was not the case. In some instances I found the descent was only from one, but, in general, it was from both parents. The knowledge of this fact may serve, not only to assist in calculating what are called the chances of lives, but it may be made useful to a physician. He may learn from it to cherish hopes of his patients in chronic, and in some acute diseases, in proportion to the capacity of life they have derived from their ancestors[67].
2. Temperance in eating and drinking. To this remark I found several exceptions. I met with one man of 84 years of age, who had been intemperate in eating; and four or five persons who had been intemperate in drinking ardent spirits. They had all been day-labourers, or had deferred drinking until they began to feel the languor of old age. I did not meet with a single person who had not, for the last forty or fifty years of their lives, used tea, coffee, and bread and butter twice a day as part of their diet. I am disposed to believe that those articles of diet do not materially affect the duration of human life, although they evidently impair the strength of the system. The duration of life does not appear to depend so much upon the strength of the body, or upon the quantity of its excitability, as upon an exact accommodation of stimuli to each of them. A watch spring will last as long as an anchor, provided the forces which are capable of destroying both, are always in an exact ratio to their strength. The use of tea and coffee in diet seems to be happily suited to the change which has taken place in the human body, by sedentary occupations, by which means less nourishment and stimulus are required than formerly, to support animal life.
3. The moderate exercise of the understanding. It has long been an established truth, that literary men (other circumstances being equal) are longer lived than other people. But it is not necessary that the understanding should be employed upon philosophical subjects to produce this influence upon human life. Business, politics, and religion, which are the objects of attention of men of all classes, impart a vigour to the understanding, which, by being conveyed to every part of the body, tends to produce health and long life.
4. Equanimity of temper. The violent and irregular action of the passions tends to wear away the springs of life.