Appetite, and hunger, are not synonymous terms with the mere habit-craving for food which most people consider to be either appetite or hunger. Real hunger, or appetite, only comes to the body when the body has earned it. There must be an expenditure of tissue, which the body requires to be repaired; or there must be a real need for energy to carry on work before the body will manifest its need for energy-supplying material. In other words, the body cares nothing about our likes or dislikes, our whims or our fancies, in the nature of food, save when it has a real need for food. Professor Chittenden demonstrated that most people simply eat the entire round of meals from mere habit. The disturbance when for any reason they miss one or two meals from the accustomed routine is simply the outcry of a habit and not the outcry of a real need. While Dr. Kellogg advises that no meal be missed, yet he also strongly advises us not to eat unless really hungry, merely drinking a little fruit juice or something of the kind at the meal hour in order to keep up the normal action of the digestive organs.
The digestive juice which is manufactured by the body when it is really hungry and food has been given to it has been shown by Pawlow and Hanecke to be the most important element in digestion. The chemical juices produced in the stomach and intestines while food is in them is of small importance and value compared with the juices that are formed while food is being chewed when the body has a good appetite or is really hungry.
This juice begins to flow at the very sight of food, and continues to from three to five minutes after beginning mastication. The production of juice in the stomach is stimulated by the contact of food with the mouth, and only during that contact; so it is obvious that the longer the food is held in the mouth, if it is held there in enjoyment, and the more completely it is chewed, so long as chewing is accompanied by taste, the more thoroughly are the flavors set free by the act of chewing, and the higher becomes the stimulating effect of these flavors upon the psychic centers which cause the appetite juice to flow into the stomach.
These facts prove the dependence of gastric digestion, or stomach digestion, upon mastication. Pawlow was experimenting with gastric juice when he hit upon this demonstration; and he has concluded that we cannot have gastric digestion at all well without thorough mouth digestion; that the complete mastication of food, in other words, is the thing necessary to prepare the stomach to receive the food. Thus, if you chew your food well, the food will be predigested in the mouth, and when it enters the stomach it will find already there waiting for it not only enough gastric juice to digest it, but just the particular kind of gastric juice that is needed.
Pawlow turned this discovery of his to a very practical use. He has a dozen or more healthy dogs which he calls his Dog Dairy. From these dogs he collects daily a quart or more of gastric juice, or appetite juice; and the dogs produce this large quantity without taking a particle of food into their stomachs. The juice is carefully filtered, and bottled and shipped all over the world to those physicians who are in touch with Pawlow and his work, and by them are administered to human patients. It is given to those patients who are deficient in gastric juice, and is used in very obstinate cases of indigestion.
Pawlow collects his juice by having openings made in the throat and in the stomachs of the dogs. When the dogs are hungry they are given food of kinds which they particularly like, and they are allowed to smell the odor and to become excited over the prospect of eating it before they are actually allowed to have it. With the first sight and odor of this food, the dogs begin to secrete the appetite juice, which flows from the opening made in their stomachs through tubes into receptacles. Then when they begin to eat their food, the food does not reach the stomach at all, but simply passes through the openings in the throat into a receptacle before the dog, and the dog can go on eating the same meal over and over again. They thus enjoy themselves thoroughly for a long time. When the appetite juice ceases to flow, the process of feeding them in this manner stops, and they are given a real meal.
VIII
HEALTH AND THE MIND
This account of Professor Pawlow’s experiment leads directly to the all important subject of the influence of mental states upon digestion and assimilation. Dr. Saleeby has published a book called “Worry, the Disease of the Age”—the very title of which shows the attitude of physicians upon this question; and the bad opinion which mankind has always entertained of such states of mind as “the blues” has now been scientifically justified. The effects of pain and pleasure upon digestion have been demonstrated by actual experiments in the laboratory of the St. Petersburg professor.
A vivid account of these experiments has been given to the writers by Dr. J. H. Kellogg, who witnessed them about a year ago. Dr. Kellogg writes:
“Professor Pawlow took Professor Benedict and myself into a quiet corner of his laboratory, and there we found a dog that had his salivary glands or ducts arranged so that by means of little tubes passing through the skin all the saliva, instead of passing down his throat, passed out through the tubes and could be collected in small glass bottles suspended beside his neck.