The importance of the initial psychic secretion of the saliva for further digestion is indicated when we realize that materials can be tasted only when dissolved in the mouth, and thereby brought into relation with the taste organs. The saliva which waters the mouth assures the dissolving of the dry but soluble food even when it is taken in large amounts.
The importance of the initial psychic secretion of gastric juice is made clear by the fact that the continued flow of this juice during digestion not only stimulates the glands of the stomach to pour out the chemical gastric juice, but by its action on the mucous membrane of the duodenum it also starts the flow of bile and pancreatic juice.
These facts are of fundamental importance in the cooking and serving of food, especially when the appetite is fickle. A bright and cheery dining-room, the daintiness of the table service, the center-piece of ferns or flowers, all are factors in exciting the pleasurable emotions, and so stimulate the appetite.
On the other hand, the digestive processes may be wholly abolished by vexation, worry, and anxiety, or when such strong emotions as anger or fear are allowed to prevail. This fact has long been known in regard to the salivary secretion, and it has now been established in regard to the secretion of the gastric juice. It is necessary to avoid all circumstances likely to provoke emotional reactions.
The inhibitory influence of excitement on the flow of the gastric juice has been studied by Professor Cannon, of Harvard University, in an interesting series of experiments on dogs. And a most important point is that the cat, which was allowed to infuriate the dog being experimented on, was only in the room for five minutes, and in spite of the fact that the animal was hungry and ate eagerly; there was almost a complete suppression of the flow of gastric juice for a period of twenty minutes.
A similar experiment was tried on a boy with a gastric fistula. Food was shown to the boy and then withheld. He was so vexed because he could not eat at once that he began to cry and flew into a towering passion, with the result that no secretion appeared even after the child was calmed. In both the case of the dog and boy there was not only a temporary inhibition of the flow of gastric juice, but it is a noteworthy fact that the effects of the emotional excitement remained long after its cause had been removed.
The practical point is, that if the digestive processes have been inhibited by emotional disturbances any food taken will lie stagnant in the stomach; and not only will there be a suppression of the gastric but of the pancreatic secretion as well, with the consequence that there is likely to be an accumulation of unabsorbed organic material in the colon and perhaps higher up as well. Bacterial decomposition will be fostered and actual harm may be done the organism.
And just as a single occasion may lead to a passing digestive disturbance, so continual mental depression, worry, or grief may permanently impair the working of the tract and so undermine the vigor and capacity of the sufferer.
It is believed that many acute attacks of indigestion in children are due to sharp rebukes administered at the table.
The Psychic Tone.—Just as there is a psychic secretion, so likewise there is a “psychic tone,” or psychic contraction of the gastro-intestinal muscles, as a result of taking food. And just as the secretory activities of the stomach are inhibited by strong emotions, so also are the movements of the stomach. And, indeed, the movements of nearly the entire alimentary canal are almost completely stopped during moments of great excitement.