We do not have to depend upon mere irresponsible guesses for the new faith in the possibility of longer life for man. Scientists have been experimenting along this line for some years, and Metchnikoff assures us that the average human life should exceed “three-score years and ten” by four decades.

He points out that the greatly increased number of persons who remain physically and mentally active past the age of seventy-five and eighty years is itself a proof that life may be prolonged. He recognizes that merely to extend existence is not a sufficient end to work for—it must be an active, worthwhile existence, and he has experimented toward this end.

All of us can recall instances of “old people” who have preserved their physical and mental faculties until their last years. We have been in the habit of regarding these people as exceptions and have perhaps not noticed that these “exceptions” are already almost frequent enough to prove that there is no such rule for longevity.

Whenever we investigate a new and wonderful thing, we find that its causes are simple and ordinary. So Metchnikoff and kindred experimenters are beginning to show us that prolonging life is a comparatively simple matter. It comes back again to diet and sleep on the physical side and to understanding of the universal laws on the mental and the emotional side of life.

All scientific men agree that nearly all of us eat too much, or eat improper food. Most of them say that we sleep too much, or try to sleep too much. They advise simple diet, varied but not heavy. It is probable that the early human being ate as the wild animals do, to appease hunger, and had to eat whatever he could find without regard to taste. As civilization advanced and he learned ways of getting increased returns from Nature, he began to select and choose what he should eat. In this way he developed “appetite” as apart from natural hunger, and as his knowledge increased, and his taste became more and more refined, appetite gradually took the place of hunger.

People ordinarily seldom know the pleasure of satisfying real hunger. Because of habit, the appetite stirs as often as three or five times a day and we gratify it. We must have certain foods prepared in a certain way. Eating becomes an end in itself, rather than merely a means to an end. If appetite is fully indulged, he becomes heavy, suffers from indigestion and sleeplessness, talks of stomach trouble and consequent “loss of appetite.” He seeks a physician to restore what he is really better without. Not every physician is as wise as the one to whom a cook once applied. She told her story of inability to eat her meals, of uncertain and unrestful sleep, increased weight, and shortness of breath. The physician heard her tale of woe and asked her the size of the family for which she cooked and about their mode of living. He learned that the family consisted of five, and that they entertained lavishly. “Do you taste all the food you prepare?” was the next question.

“Yes, sir; I must taste it to be sure it is just right.” “Ah!” replied the doctor; “put on a plate exactly the same quantity of everything that you take to taste—no more, no less—and send it to me to-morrow evening.”

Much to the cook’s astonishment, at the close of the next day, which had included a dinner-party, there was a heaping platter of food, more than she would have thought it possible to eat even at three meals.

“It is not a tonic you want,” said the physician. “You already eat too much, which accounts for your loss of appetite, shortness of breath, and sleeplessness. It may be necessary for you to taste all the food you cook, but take smaller ‘tastes’ and eat nothing else on cooking days. I cannot help you; you must help yourself.” (Being an ignorant woman, she went to another doctor and got some ill-tasting drug.)

And such is, after all, the decision of all the scientific investigators into the life and health of men: We must help ourselves by understanding the laws of life and observing them.

Most rich persons are really like the man who applied to his physician about “loss of appetite.” “Try beginning dinner with raw oysters,” said the doctor. In a few days the patient returned, to say that the oysters did no good.

“Maybe you didn’t eat enough?” said the doctor.

“Well,” said the man, “I ate four dozen.”