Everyday experience tells us the stomach mucosa is not sensitive to touch. Pavlov states: "It can hardly be doubted that under normal conditions the surface of the stomach has a certain degree of tactile sensibility." The term tactile sensibility is evidently used here in the sense of a general response to mechanical stimulation rather than as implying a true tactile sensibility. When solid food is swallowed, no tactile sensation is felt after the food has passed the pharynx, unless the mass is so large that it causes unusual distension of the esophagus. In that case it may be felt all the way down the esophagus, but this is due to the distension of the wall of the esophagus and is not a tactile sensation from contact with the mucosa.
Hertz tested on himself the tactile sensibility of the mucosa of the esophagus by means of an esophagoscope with a slit down the side, so that a metal bulb in a long holder could be moved along the mucous membrane of the esophagus and the pharynx. The pharyngeal mucosa was found to be sensitive to touch; the esophageal was insensitive.
The author has tested the tactile sensibility of his own gastric mucosa, swallowing a good-sized rubber tube, through which was passed a test-tube brush attached to a strong piano wire. Pulling the test-tube brush about in the cavity of the stomach produced no sensation.
Numerous tests were made on the gastric mucosa of Mr. V., our gastric fistula case. Gently touching or striking the mucosa with blunt objects produced no sensation. If the mucosa is rubbed or pressed very vigorously with a blunt object Mr. V. says he "can feel it"; he cannot describe the sensation thus produced except in a negative way. It is not like touch, nor is it pain or hunger. Whatever the character of the sensation may be, we are satisfied that it is a real change in the stream of consciousness, for he recognizes these stimuli when he has no other means of knowing that the gastric mucosa is being handled. The sensation may not originate in the mucosa, but in the muscularis (tonus relaxation through reflex inhibition) or possibly in the visceral peritoneum, as the pressure must be considerable to produce it. We are satisfied that the stimulation of the normal gastric mucosa of Mr. V. does not produce tactile sensation. The same conclusion has been reached by previous workers using human.gastric fistula cases.