"Mastication increases the amount of alkaline saliva passing into the stomach, and this not only prolongs the period of starch digestion within this organ, but, by its influence upon the reaction of the gastric contents, influences all the digestive processes taking place there."

7 Chittenden: "Nutrition of Man," pp. 18-19. 8 Campbell: Lecture quoted in "The A. B. - Z. of Our Own Nutrition," p. 109.

When the action of the saliva has been ended, the gastric juice takes up the work of digesting the fats and proteids. As in the case of saliva, the scientists have been finding out some new things in regard to this fluid which have greatly modified their ideas in regard to the whole subject of nutrition. It was formerly thought that the secretion of gastric juice was caused by the contact of the food with the stomach walls. A short time ago, however, Professor J. P. Pavlov, director of the Department of Experimental Physiology in the Russian Military School of Medicine at St. Petersburg, by a series of experiments upon dogs, established positively that the flow of gastric juice was caused primarily, not by contact of the food with the stomach-walls, but by a keen desire for food and by the pleasure of eating it - that is, by appetite and taste.

"Pavlov has clearly shown," says Professor Chittenden, "that the gastric juice is started by impulses which have their origin in the mouth and nostrils; the sensation of eating, the smell, sight, and taste of food serving as psychical stimuli, which call forth a secretion from the stomach glands, just as the same stimuli may induce an outpouring of saliva. These sensations, as Pavlov has asserted, affect secretory centers in the brain, and impulses are thus started which travel downward to the stomach through the vagus nerves, and as a result gastric juice begins to flow." 9

The first and mightiest exciter of the secre-tory nerves of the stomach, therefore, is the appetite. After appetite, the chief agent for the production of gastric juice is a keen sense of the pleasant taste of food. As the finer degrees of appreciation can be achieved only when food is finely divided, subjected to the transforming action of saliva, and passed slowly over the "taste-buds" in the mouth, it can readily be seen that mastication plays an important part in this process.

"The mere chewing of food," says Dr. Daniel S. Sager, " is sufficient to cause an abundant flow of gastric juice. The longer the food is held in the mouth, the greater the impression made on the nerves of taste. Through these nerves the appetite center is stimulated, and from this center are sent out to the stomach powerful nervous impulses which excite the glands to activity whereby powerful appetite juice is produced. When food is swallowed quickly, its various flavors are little appreciated. The excitation produced is of no consequence, and the amount of juice secreted will be very small; whereas if the food is retained in the mouth and masticated until every particle of sapid substance is extracted from it, there is an abundant flow of juice and the greatest good is derived from it. When food is eaten in the ordinary hasty manner, the taste is swallowed with it, the palate is stimulated only to a very moderate extent, very little appetite juice is produced, and digestion fails in consequence." 10

9 Chittenden: " Nutrition of Man," pp. 23-34.

Dr. Harry Campbell says: "It is now known that mastication acts reflexly upon the stomach, promoting the flow of gastric juice, and thus preparing the stomach for the entrance of the food into it. Food introduced into the stomach, unaccompanied by mastication, is less effective in promoting the gastric flow. It is probable that the influence of mastication on the flow of gastric juice is largely produced through the medium of psychic influences, for the more efficient the mastication, the more is the sense of taste affected."11

10 Sager: "The Art of Living in Good Health," pp. 23-24.

As in the case of saliva, the gastric secretions are stimulated by pleasure and checked by distress. Through observations on animals by means of the Rontgen Ray, scientists have been able actually to watch this law at work. By mixing with the food a small quantity of subnitrate of bismuth, a tasteless and practically harmless substance which is opaque to the Röntgen Ray, Dr. W. B. Cannon, of the physiological laboratory of the Harvard Medical School, showed by ocular demonstration, that as long as the subject of the experiment, a female cat, was kept happy and comfortable, the food passed rapidly and rhythmically along the digestive tract, but as soon as the cat was hurt or annoyed, the movements stopped short and the food remained stationary until the cat was once more made comfortable or restored to a good humor.12

11 Campbell: Lecture quoted in "The A. B. - Z, of Our Own Nutrition," pp. 109-103.

As food is brought into proper condition by the stomach, it is permitted to pass gradually into the small intestine where digestion is completed and the absorption of the prepared food material into the blood is begun.

"The intestine," says Professor Chittenden, "is a much more important part of the alimentary tract" (than the stomach); "it is likewise far more sensitive to changing conditions than the stomach, and undoubtedly one function of the latter organ is to protect the intestine and preserve it from insult. The stomach may be compared to a vestibule or reservoir, capable of receiving without detriment moderately large amounts of food, together with fluid, in different forms and combinations, with the power to hold them there until by action of the gastric juice they are so transformed that their onward passage into the intestine can be permitted with perfect safety. Then, small portions of the properly prepared material may be discharged from time to time through the pylorus without danger of overloading the intestine, and in a form capable of undergoing rapid and complete digestion. Further, the stomach as a reservoir is very useful in bringing everything to a proper and constant temperature before allowing its entry into the intestine. . . . The great bulk of the digested food material is absorbed from the small intestine, and there are two pathways open through which the absorbed material can gain access to the blood.