“But how is a person to know when he has chewed a mouthful long enough?” the reader asks. Mr. Fletcher answers that nature has provided us with a food filter—an automatic safety device. Professor Hubert Higgins, formerly demonstrator of anatomy at Cambridge University in England, and Professor Hasheby of Brussels, Belgium, have lately conducted a series of experiments which throw light on this question on its scientific side. At the back of the tongue there are a number of little knobs, which are really taste buds, or apparatus for the tasting of food. During the time that mastication is going on, the mouth is closed and is completely air tight, and germproof. This fact one can readily demonstrate by filling out the lips with air. The mouth is full of air, yet one can breathe behind this curtain of air, showing that the mouth is thoroughly cut off. This is what happens during mastication, for of course one should masticate with the lips closed. Now, when the food has become sufficiently ensalivated, or mixed up, the circumvallate papillæ at the back of the throat, where the taste buds are, relax, and behind that the soft palate forms a negative pressure. This soft palate is muscled just as it is in the horse—which is an animal that masticates, but is not found in the dog, which is an animal that bolts its food. Whenever the food is ready for the body, the soft palate relaxes, and is sucked back, and the swallowing of a mouthful of the prepared food takes place involuntarily. The body is thus supplied with as perfect a protection as could be devised, and perfectly automatic; all that is necessary being that one should masticate the food until it naturally disappears. One must not attempt to keep the food too long in the mouth, but let it have its own course. There are some sorts of food which, when one has chewed them three or four times, are sucked up, showing that they have received all the mouth treatment that nature requires they should. With other foods one can masticate up to one hundred and fifty times, and still they are not sucked up. This food filter is a perfectly instinctive apparatus; but as people have acquired the habit of flavoring foods with artificial sauces and relishes, most of them have spoiled this protective device. In the words of Mr. Fletcher himself: “This is a gift of Nature to man which we have been neglecting. It is not a gift which has been given to me and a few others alone. I think everybody could acquire the use of it if they would give Nature a chance by eating slowly, by eating with a sense of enjoyment, and by never eating save when they are really hungry and in a mood to enjoy the food.” III THE YALE EXPERIMENTS