Our gastric fistula man, Mr. V., offers an exceptional opportunity for studying the relations of certain conscious states, particularly those associated with foods and with eating, on the activities of the empty stomach. The esophagus is completely closed at the level of the upper end of the sternum, so that nothing can enter the stomach from the mouth. The swallowing mechanisms are normal, and the man can swallow and hold in the esophageal pouch about 25 c.c. of material. The gustatory (and olfactory) sense is normal. The senses of thirst and hunger are normal. He masticates his food in the usual way, and the chewing processes are accompanied by the normal conscious states. The masticated food is placed in a syringe and introduced into the stomach through the fistula, which does not involve any pain or discomfort, and the man is adjusted to this condition, as this has been his method of feeding for the last twenty years. Because of the ample size of the gastric fistula the man may sit down at the dinner table, see, smell, taste, and chew his food in the usual manner up to the point of introducing the food through the fistula, while tracings are being taken of a tonus and the movements of the stomach, and records made of the secretion of the gastric juice.
We know, particularly through the researches of Pavlov on dogs, and from many observations on man, that when appetite is present the sight, smell, taste (especially taste) of palatable foods causes a reflex secretion of gastric juice, the so-called "psychic secretion." The efferent nerve-fibers for this reflex reach the stomach through the vagi. The more recent work of Cannon and others has demonstrated that the tonus of the stomach musculature is also primarily dependent on efferent nervous impulses through the vagi. A certain degree of tonus is normally a prerequisite for peristalsis or contractions in the empty stomach. The suggestion is therefore obvious that the same stimuli which lead to psychic secretion of gastric juice may at the same time cause an augmentation of the tonus and the contractions of the stomach musculature. Cannon postulated such a "psychic tonus," but no evidence for its existence has been recorded.
It is a universal experience of normal persons that the sight or smell (or even the memory) bf palatable foods seems to induce hunger and appetite, or intensify these sensations if they are already present. The simplest explanation of this fact would be that the smell or taste of palatable foods initiates or augments the stomach contractions, thus increasing the hunger sensation by increasing the intensity of the gastric stimulation. The facts, at least in man and dogs, are the very opposite of those demanded by this hypothesis.
There are two sources of error in experiments of this character. In the first place, the periods of contraction of the empty stomach vary in intensity and duration, and the intervening periods of relative quiescence vary in length. The periods of quiescence may be interrupted by occasional contractions. This being the case, the initiation of stomach contractions simultaneously with tasting palatable food during quiescence of the stomach, for example, may • be a mere coincidence. An augmentation of the contractions seemingly due to tasting food during a contraction period may simply be the usual increase in strength of the stomach contraction during such period. In the same way, if tasting food toward the end of a contraction period should be followed by cessation of the stomach contractions, this apparent inhibition may be a coincidence, the cessation of the contractions being "spontaneous" and not casually connected with the tasting of food. These difficulties were realized before the work was undertaken, as it was preceded by an extended survey of the "spontaneous" stomach movements when not interfered with experimentally. Because of the variability of the "spontaneous" stomach activity, the individual test must be repeated a great number of times, and little or no significance can be ascribed to exceptional results.
A source of error, more serious because not so readily controlled, lies in certain subjective states of an inhibitory character. Pavlov found that while the sight and smell of palatable foods ordinarily caused "psychic" secretion of gastric juice in dogs when hungry, if the dogs knew from past experience that they were not to be permitted to eat the food, the same stimuli caused no secretion. We may have analogous conditions in regard to the stomach tonus and movements. It is possible that, no matter how great the hunger or appetite in man, the knowledge that the seeing, smelling, or tasting food was part of an experiment might initiate cerebral processes of an inhibitory character. This source of error has been controlled in two ways: (1) in Mr. V.'s case the mastication or tasting food was made part of his ordinary routine in preparing the food to be put into the stomach, and the man knew that as soon as the food was prepared it would be introduced into the stomach in the usual way; (2) records were made of the presence or absence of the psychic secretion of gastric juice. If the tasting and chewing of food start a copious flow of gastric juice, we can infer that the tasting and chewing do not give rise to cerebral processes of an inhibitory character.