Certain remarkable experiments conducted by Rogers, Metchnikoff, and Pawlow in Europe, and by Cannon and Kellogg in America, have thrown a new and interesting light upon the ideas of Fletcher; proving that the act of chewing the food gives to the nerves that control the digestive fluids an opportunity to assay the food, to test it and select for it the particular kind of digestive fluid which that particular kind of food requires. It appears that there are many different kinds of saliva, and each one of these kinds has a particular kind of work to do, which no other kind is able to do. Metchnikoff has shown that if one takes cane sugar into the mouth with or without other food, there is manufactured by the salivary glands a certain peculiar fluid which digests cane sugar. If the cane sugar is not taken into the mouth, then that substance is not made. The saliva that flows into the mouth when there is food there but no cane sugar with the food, will not digest cane sugar. So it readily can be seen that if cane sugar should be hastily swallowed, it is much less likely to be properly digested. And this holds good with nearly all other kinds of food.
THE “FOOD FILTER”
“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
At Yale University, Professor Russell H. Chittenden, Director of the Sheffield Scientific School, Lafayette B. Mendel, Professor of Physiological Chemistry, and Irving Fisher, Professor of Political Economy, have carried on a long series of experiments, begun six years ago as a test of the claims made by Fletcher. The net results of these experiments up to date (for they are still in progress) may be put into a nutshell. The following statement was drawn up by one of the writers of this book and submitted to Professors Chittenden and Fisher, who have accepted it as a summary of their present views:
“The commonly accepted standards which claim to tell the quantity of food needed each day by the average man are based upon many careful observations of what men actually do eat.
“We challenge these standards, however, as the exact science of to-day cannot accept as authority common customs and habits in any attempt to ascertain the right principles of man’s nutrition, since experiments have demonstrated how readily one set of habits may be substituted for another and how easily wrong habits become hardened into laws. The evidence presented by observers of common customs, while they must be duly considered, cannot, therefore, be taken as proof that these habits and customs are in accord with the true physiological needs of the body.
“We believe that the following propositions have been demonstrated as truths by the experiments we have made at Yale.