(Discusses various foods and their food values, the quantities we need, and their money cost.) I think there is no more important single question about health than the question of how much food we should eat. It is one about which there is a great deal of controversy, even among the best authorities. We shall try here for a common-sense solution. At the outset we have to remind ourselves of the distinction we tried to draw between nature and man. To what extent can civilized man rely upon his instincts to keep him in perfect health? Let us begin by considering the animals. How is their diet problem solved? Horses and cattle in a wild state are adjusted to certain foods which they find in nature, and so long as they can find it, they have no diet problem. Man comes, and takes these animals and domesticates them; he observes their habits, and gives to them a diet closely approaching the natural one, and they get along fairly well. But suppose the man, with his superior skill in agriculture, taking wild grain and planting it, reaping and threshing it by machinery, puts before his horse an unlimited quantity of a concentrated food such as oats, which the horse can never get in a natural state--will that horse's instincts guide it? Not at all. Any horse will kill itself by overeating on grain. I have read somewhere a clever saying, that a farm is a good place for an author to live, provided he can be persuaded not to farm it. But once upon a time I had not heard that wise remark, and I owned and tried to run a farm. I had two beautiful cows of which I was very proud, and one morning I woke up and discovered that the cows had got into the pear orchard and had been feeding on pears all night. In a few hours they both lay with bloated stomachs, dying. A farmer told me afterwards that I might have saved their lives, if I had stuck a knife into their stomachs to let out the gas. I do not know whether this is true or not. But my two dead cows afford a perfect illustration of the reason why civilized man cannot rely upon his instincts and his appetites to tell him when he has had enough to eat. He can only do this, provided he rigidly restricts himself to the foods which he ate in the days when his teeth and stomach and bowels were being shaped by the process of natural selection. If he is going to eat any other than such strictly natural foods, he will need to apply his reason to his diet schedule.