The Theory That Hunger is a General Sensation
The conception that hunger arises from a general condition of the body rests in turn on the notion that, as the body uses up material, the blood becomes impoverished. Schiff[5] advocated this notion, and suggested that poverty of the blood in food substance affects the tissues in such manner that they demand a new supply. The nerve cells of the brain share in this general shortage of provisions, and because of internal changes, give rise to the sensation. Thus is hunger explained as an experience dependent on the body as a whole.
Three classes of evidence are cited in support of this view:
1. “Hunger increases as time passes”—a partial statement. The development of hunger as time passes is a common observation which quite accords with the assumption that the condition of the body and the state of the blood are becoming constantly worse, so long as the need, once established, is not satisfied.
While it is true that with the lapse of time hunger increases as the supply of body nutriment decreases, this concomitance is not proof that the sensation arises directly from a serious encroachment on the store of food materials. If this argument were valid we should expect hunger to become more and more distressing until death follows from starvation. There is abundant evidence that the sensation is not thus intensified; on the contrary, during continued fasting hunger, at least in some persons, wholly disappears after the first few days. Luciani,[6] who carefully recorded the experience of the faster Succi, states that after a certain time the hunger feelings vanish and do not return. And he tells of two dogs that showed no signs of hunger after the third or fourth day of fasting; thereafter they remained quite passive in the presence of food. Tigerstedt,[7] who also has studied the metabolism of starvation, declares that although the desire to eat is very great during the first day of the ordeal, the unpleasant sensations disappear early, and that at the end of the fast the subject may have to force himself to take nourishment. The subject, “J. A.,” studied by Tigerstedt and his co-workers,[8] reported that after the fourth day of fasting, he had no disagreeable feelings.
Carrington,[9] after examining many persons who, to better their health, abstained from eating for different periods, records that “habit-hunger” usually lasts only two or three days and, if plenty of water is drunk, does not last longer than three days. Viterbi,[10] a Corsican lawyer condemned to death for political causes, determined to escape execution by depriving his body of food and drink. During the eighteen days that he lived he kept careful notes. On the third day the sensation of hunger departed, and although thereafter thirst came and went, hunger never returned. Still further evidence of the same character could be cited, but enough has already been given to show that after the first few days of fasting the hunger feelings may wholly cease. On the theory that hunger is a manifestation of bodily need, are we to suppose that, in the course of starvation, the body is mysteriously not in need after the third day, and that therefore the sensation of hunger disappears? The absurdity of such a view is obvious.
2. “Hunger may be felt though the stomach be full”—a selected alternative. Instances of duodenal fistula in man have been carefully studied, which have shown that a modified sensation of hunger may be felt when the stomach is full. A famous case described by Busch[11] has been repeatedly used as evidence. His patient, who lost nutriment through a duodenal fistula, was hungry soon after eating, and felt satisfied only when the chyme was restored to the intestine through the distal fistulous opening. As food is absorbed mainly through the intestinal wall, the inference is direct that the general bodily state, and not the local conditions of the alimentary canal, must account for the patient’s feelings.
A full consideration of the evidence from cases of duodenal fistula cannot so effectively be presented now as later. That in Busch’s case hunger disappeared while food was being taken is, as we shall see, quite significant. It may be that the restoration of chyme to the intestine quieted hunger, not because nutriment was thus introduced into the body, but because the presence of material altered the nature of gastro-intestinal activity. The basis for this suggestion will be given in due course.
3. “Animals may eat eagerly after section of their vagus and splanchnic nerves”—a fallacious argument. The third support for the view that hunger has a general origin in the body is derived from observations on experimental animals. By severance of the vagus and splanchnic nerves, the lower esophagus, the stomach and the small intestine can be wholly separated from the central nervous system. Animals thus operated upon nevertheless eat food placed before them, and may indeed manifest some eagerness for it.[12] How is this behavior to be accounted for—when the possibility of local stimulation has been eliminated—save by assuming a central origin of the impulse to eat?
The fallacy of this evidence, though repeatedly overlooked, is easily shown. We have already seen that appetite as well as hunger may lead to the taking of food. Indeed, the animal with all gastro-intestinal nerves cut may have the same incentive to eat that a well-fed man may have, who delights in the pleasurable taste and smell of food and knows nothing of hunger pangs. Even when the nerves of taste are cut, as they were in Longet’s experiments,[13] sensations of smell are still possible, as well as agreeable associations which can be roused by sight. More than fifty years ago Ludwig[14] pointed out that, even if all the nerves were severed, psychic reasons could be given for the taking of food, and yet because animals eat after one or another set of nerves is eliminated, the conclusion has been drawn by various writers that the nerves in question are thereby proved to be not concerned in the sensation of hunger. Evidently, since hunger is not required for eating, the act of eating is no testimony whatever that the animal is hungry, and, after the nerves have been severed, is no proof that hunger is of central origin.