The Concomitance of Contractions and Hunger in Man
Although the evidence above outlined had led me to the conviction that hunger results from contractions of the alimentary canal, direct proof was still lacking. In order to learn whether such proof might be secured, Washburn determined to become accustomed to the presence of a rubber tube in the esophagus.[*] Almost every day for several weeks Washburn introduced as far as the stomach a small tube, to the lower end of which was attached a soft-rubber balloon about 8 centimeters in diameter. The tube was thus carried about each time for two or three hours. After this preliminary experience the introduction of the tube and its presence in the gullet and stomach were not at all disturbing. When a record was to be taken, the balloon, placed just within the stomach, was moderately distended with air, and was connected with a water manometer ending in a cylindrical chamber 3.5 centimeters wide. A float recorder resting on the water in the chamber permitted registering any contractions of the fundus of the stomach. On the days of observation Washburn would abstain from breakfast, or eat sparingly; and without taking any luncheon would appear in the laboratory about two o’clock. The recording apparatus was arranged as above described. In order to avoid any error that might arise from artificial pressure on the balloon, a pneumograph, fastened below the ribs, was made to record the movements of the abdominal wall. Uniformity of these movements would show that no special contractions of the abdominal muscles were made. Between the records of gastric pressure and abdominal movement, time was marked in minutes, and an electromagnetic signal traced a line which could be altered by pressing a key. All these recording arrangements were out of Washburn’s sight; he sat with one hand at the key, ready whenever the sensation of hunger was experienced to make the current which moved the signal.
[*] Nicolai (loc. cit.) reported that although the introduction of a stomach tube at first abolished hunger in his subjects, with repeated use the effects became insignificant.
Sometimes the observations were started before any hunger was noted; at other times the sensation, after running a course, gave way to a feeling of fatigue. Under either of these circumstances there were no contractions of the stomach. When Washburn stated that he was hungry, however, powerful contractions of the stomach were invariably being registered. As in my own earlier experience, the sensations were characterized by periodic recurrences with free intervals, or by periodic accesses of an uninterrupted ache. The record of Washburn’s introspection of his hunger pangs agreed closely with the record of his gastric contractions. Almost invariably, however, the contraction nearly reached its maximum before the record of the sensation was started (see [Fig. 37]).
Figure 37.—One-half the original size. The top record represents intragastric pressure (the small oscillations due to respiration, the large to contractions of the stomach); the second record is time in minutes (ten minutes); the third record is W’s report of hunger pangs; the lowest record is respiration registered by means of a pneumograph about the abdomen.
This fact may be regarded as evidence that the contraction precedes the sensation, and not vice versa, as Boldireff considered it. The contractions were about a half-minute in duration, and the intervals between varied from thirty to ninety seconds, with an average of about one minute. The augmentations of intragastric pressure in Washburn ranged between eleven and thirteen in twenty minutes; I had previously counted in myself eleven hunger pangs in the same time. The rate in each of us was, therefore, approximately the same. This rate is slightly slower than that found in dogs by Boldireff; the difference is perhaps correlated with the slower rhythm of gastric peristalsis in man compared with that in the dog.[37]
Before hunger was experienced by Washburn the recording apparatus revealed no signs of gastric activity. Sometimes a rather tedious period of waiting had to be endured before contractions occurred. And after they began they continued for a while, then ceased (see [Fig. 38]). The feeling of hunger, which was reported while the contractions were recurring, disappeared as the waves stopped. The inability of the subject to control the contractions eliminated the possibility of their being artifacts, perhaps induced by suggestion. The close concomitance of the contractions with hunger pangs, therefore, clearly indicates that they are the real source of those pangs.
Figure 38.—One-half the original size. The same conditions as in [Fig. 37]. (Fifteen minutes.) There was a long wait for hunger to disappear. After x, W. reported himself “tired but not hungry.” The record from y to z was the continuance, on a second drum, of x to y.
Boldireff’s studies proved that when the empty stomach is manifesting periodic contractions, the intestines also are active. Conceivably all parts of the alimentary canal composed of smooth muscle share in these movements. The lower esophagus in man is provided with smooth muscle. It was possible to determine whether this region in Washburn was active during hunger.
To the esophageal tube a thin-rubber finger-cot (2 centimeters in length) was attached and lowered into the stomach. The little rubber bag was distended with air, and the tube, pinched to keep the bag inflated, was gently withdrawn until resistance was felt. The air was now released from the bag and the tube farther withdrawn about 3 centimeters. The bag was again distended with air at a manometric pressure of 10 centimeters of water. Inspiration now caused the writing lever, which recorded the pressure changes, to rise; and a slightly farther withdrawal of the tube changed the rise, on inspiration, to a fall. The former position of the tube, therefore, was above the gastric cavity and below the diaphragm. In this position the bag, attached to a float recorder (with chamber 2.3 centimeters in diameter), registered the periodic oscillations shown in [Fig. 39]. Though individually more prolonged than those of the stomach, these contractions, it will be noted, occur at about the same rate.
Figure 39.—One-half the original size. The top record represents compression of thin rubber bag in the lower esophagus. The pressure in the bag varied between 9 and 13 centimeters of water. The cylinder of the recorder was of smaller diameter than that used in the gastric records. The esophageal contractions compressed the bag so completely that, at the summits of the large oscillations, the respirations were not registered. When the oscillations dropped to the time line, the bag was about half inflated. The middle line registers time in minutes (ten minutes). The bottom record is W’s report of hunger pangs.
This study of hunger, reported by Washburn and myself in 1912, has since been taken up by Carlson of Chicago, and in observations on a man with a permanent gastric fistula, as well as on himself and his collaborators, he has fully confirmed our evidence as to the relation between contractions of the alimentary canal and the hunger sensation. In a series of nearly a score of interesting papers, Carlson and his students[38] have greatly amplified our knowledge of the physiology of the “empty” stomach. Not only are there the contractions observed by Washburn and myself, but at times these may fuse into a continuous cramp of the gastric muscle. The characteristic contractions, furthermore, continue after the vagus nerve supply to the stomach has been destroyed, and, therefore, are not dependent on the reception of impulses by way of the cranial autonomic fibres. Recently Luckhardt and Carlson have brought forward evidence that the blood of a fasting animal if injected into the vein of a normal animal is capable of inducing in the latter the condition of cramp or tetanus in the gastric muscle mentioned above—an effect which does not occur when the blood of a well-fed animal is injected. It seems possible that a substance exists in the blood which acts to excite the gastric hunger mechanism. But this point will require further investigation.
With these demonstrations that contractions are the immediate cause of hunger, most of the difficulties confronting other explanations are readily obviated. Thus the sudden onset of hunger and its peculiar periodicity—phenomena which no other explanation of hunger can account for—are at once explained.
In fever, when bodily material is being most rapidly used, hunger is absent. Its absence is understood from an observation made by F. T. Murphy and myself,[39] that infection, with systemic involvement, is accompanied by a total cessation of all movements of the alimentary canal. Boldireff observed that when his dogs were fatigued the rhythmic contractions failed to appear. Being “too tired to eat” is thereby given a rational explanation.
A pathological form of the sensation—the inordinate hunger (bulimia) of certain neurotics—is in accordance with the well-known disturbances of the tonic innervation of the alimentary canal in such individuals.
Since the lower end of the esophagus, as well as the stomach, contracts periodically in hunger, the reference of the sensation to the sternum by the ignorant persons questioned by Schiff was wholly natural. The activity of the lower esophagus also explains why, after the stomach has been removed, or in some cases when the stomach is distended with food, hunger can still be experienced. Conceivably the intestines also originate vague sensations by their contractions. Indeed, the final banishment of the modified hunger sensation in the patient with duodenal fistula, described by Busch, may have been due to the lessened activity of the intestines when chyme was injected into them.
The observations recorded in this paper have, as already noted, numerous points of similarity to Boldireff’s observations[40] on the periodic activity of the alimentary canal in fasting dogs. Each period of activity, he found, comprised not only widespread contractions of the digestive canal, but also the pouring out of bile, and of pancreatic and intestinal juices rich in ferments. Gastric juice was not secreted at these times; when it was secreted and reached the intestine, the periodic activity ceased. What is the significance of this extensive disturbance? I have elsewhere presented evidence[41] that gastric peristalsis is dependent on the stretching of gastric muscle when tonically contracted. The evidence that the stomach is in fact strongly contracted in hunger—i. e., in a state of high tonus—has been presented above.[*] Thus the very condition which causes hunger and leads to the taking of food is the condition, when the swallowed food stretches the shortened muscles, for immediate starting of gastric peristalsis. In this connection the observations of Haudek and Stigler[42] are probably significant. They found that the stomach discharges its contents more rapidly if food is eaten in hunger than if not so eaten. Hunger, in other words, is normally the signal that the stomach is contracted for action; the unpleasantness of hunger leads to eating; eating starts gastric digestion, and abolishes the sensation. Meanwhile the pancreatic and intestinal juices, as well as bile, have been prepared in the duodenum to receive the oncoming chyme. The periodic activity of the alimentary canal in fasting, therefore, is not solely the source of hunger pangs, but is at the same time an exhibition in the digestive organs of readiness for prompt attack on the food swallowed by the hungry animal.
[*] The “empty” stomach and esophagus contain gas (see Hertz: Quarterly Journal of Medicine, 1910, iii, p. 378; Mikulicz: Mittheilungen aus den Grenzgebieten der Medicin und Chirurgie, 1903, xii, p. 596). They would naturally manifest rhythmic contractions on shortening tonically on their content.