But it may be asked, is not appetite a safe guide to follow? Do not the cravings of the stomach and the so-called pangs of hunger merit consideration? Is it not the part of wisdom to follow inclination in the choice and quantity of our food? Can we not safely rely upon these factors as an index of the real needs of the body? If these questions are to be answered in the affirmative, then it is plain that a study of dietetic customs will tell us definitely how much food and what kinds of food are required daily to supply the true wants of the body. There are writers who claim that instinct is a perfectly safe guide to follow; that it is far superior to reason; but it is to be noticed that most of these writers, if they have any physiological knowledge to draw upon, are sooner or later prone to admit that the body has certain definite needs which it is the purpose of food to supply, with the added implication that any surplus of food over and above what is necessary to meet these demands is entirely uncalled for. Thus, one such writer states that “the man in the street follows his God-given instincts and plods peacefully along to his three square meals a day, consisting of anything he can find in the market, and just as much of it as he can afford, with special preference for rich meats, fats, and sugars.” Yet this same writer, a little later, emphasizes the fact that “every particle of the energy which sparkles in our eyes, which moves our muscles, which warms our imaginations, is sunlight cunningly woven into our food by the living cell, whether vegetable or animal. Every movement, every word, every thought, every aspiration represents the expenditure of precisely so much energy derived from food.” Why, then, would it not be wise to ascertain how much energy is so expended, on an average, during the day’s activity and govern the intake of food accordingly? Why not apply an intelligent supervision in place of following an instinct which, in the words of the author just quoted, leads one on to consume “anything he can find in the market and just as much of it as he can afford”? Truly, if dietetic customs and the habits of mankind are the results of instinct working in this fashion, there cannot be much value in the data obtained by observing the quantities of food mankind is in the habit of eating. Dietary standards based on such observations must be open to the suspicion of representing values far above the actual needs of the body.