The close parallel between the degree of tke stomach contractions and the intensity of the hunger sensations is further shown by the fact that the beginning of a strong contraction is frequently signaled by key No. 2 (moderate hunger), and then a shift made to key No. 3 (strong hunger) nearer the apex of the. contraction. Evidently, it is possible to distinguish a gradually increasing intensity of the hunger sensation during and parallel with the individual hunger contractions in the stomach. But this distinction is never made in very strong hunger and corresponding contractions.
Fusion of the hunger sensations into hunger tetanus parallel with strong and rapid contractions or tetanus of the stomach contractions.- The essential features and conditions of the incomplete tetanus of the stomach contraction at the end of the period of very vigorous contractions are already familiar to the reader. These tetanus periods of the stomach are invariably accompanied by a similar fusion or tetanus of the hunger sensation. The fusion of the hunger sensation appears to be more complete than the fusion of the stomach contractions. When the rate of the strong stomach contractions approaches 2 per minute, the fusion of the hunger sensations is practically complete, that is, a person is then unable to distinguish any rhythmical variations in the hunger intensity. These phases of the stomach contractions are always signaled with key No. 3 (strongest hunger). The greater fusion of the hunger sensations than is shown by the synchronous stomach contractions is probably due to the tonus element, as a strong and persistent state of tonus gives rise to a continuous hunger sensation. The fact that the strong individual sensations lag or persist longer than the corresponding stomach contractions may also be a factor.
The abrupt cessation of the gastric tetanus at the end of a strong contraction period is accompanied by an equally abrupt and complete cessation of the hunger sensations.
Individual contractions of the "20-seconds rhythm" may give rise to a mild hunger pang, in which case they are usually stronger than those not definitely recognized in consciousness. But occasionally there may be no marked difference in the amplitude of the contractions. Each consecutive contraction of the " 20-seconds rhythm" is never signaled as a hunger contraction unless the contractions are very strong, in which case they can hardly be distinguished from the moderate contraction of the periodic or "30-seconds rhythm."
Assuming that the " 20-seconds rhythm" is an antrum rhythm, and that the stomach contractions cause the hunger sensations, it follows that strong contractions of the pyloric region should cause hunger. Now, such strong contractions of this region of the stomach occur during vomiting, yet vomiting is, to our knowledge, never accompanied by hunger sensations, although epigastric pain and distress may be felt. Of course it is possible that the change in the physiological condition in the central and the gastric nervous mechanisms usually present in vomiting may account for the absence of hunger. The recognition of only an occasional contraction of the "20-seconds rhythm" as a hunger contraction when all the contractions are of nearly uniform intensity is probably due to variations in attention.
The significance of the time relations between the stomach contractions and the hunger sensations.-It was pointed out by Cannon and Washburn that the time relations between the stomach contractions and the hunger sensations might serve to determine the nature of their causal relationship. It is doubtful, however, whether the data secured by the methods so far employed are of much significance as regards this point. Unless the balloon in the stomach completely fills the stomach cavity and the pressure in the balloon is very slight, it is clear that the manometer does not register the very beginnings of the contractions. And on the subjective side we have the fluctuation of attention as a source of error.
The recognition of the stomach contraction as a hunger pang depends not only on the strength of the contraction, but also on the rapidity of development of the contraction phase; that is, two contractions may indicate equal degrees of shortening of the stomach musculature, but if the contraction phase of one covers a minute or more, while that of the other half a minute or less, the latter contraction only is accompanied by a definite hunger sensation. The stomach may thus exhibit slow tonus undulations of considerable magnitude without any attendant hunger feeling. This relation of the rate of the contraction of the hunger sensation is in accord with one of the general "laws of stimulation," and would seem to strengthen the view that the sensation is the result of the contraction.
In no instance out of the numerous tests made on man was the hunger felt before the beginning of the stomach contractions. But when the balloon and the manometer are adjusted as delicately as possible, the hunger signal and stomach contractions appear nearly simultaneously. But inasmuch as the manometer probably does not register the very beginning of the contractions, it is evident that some seconds of the contraction phase always precede the hunger feeling.
When the stomach contraction is of moderate strength and hunger sensation of correspondingly moderate intensity, the hunger sensation usually ceases at the height of the contraction, but when the contractions are very strong the hunger sensation persists also during the relaxation phase. In other words, the sensation lags, both at the beginning and at the end of the contraction.
A certain degree of constant or tonic contraction in the empty stomach appears to give rise to a continuous hunger sensation.-This sensation is a somewhat incomplete feeling of tension or pressure in the epigastric region, but usually less intense and less definitely localized than the pangs of hunger caused by the strong rhythmical contractions. This constant epigastric tension may thus be present during an entire hunger period lasting for 15 to 60 minutes or more, but augmented to distinct hunger pangs with each strong contraction. The degree of tonus or constant contraction of the stomach during a hunger period differs with the individual man, and this tonus is not in evidence in some of the lower animals. But it is likely that close introspection will reveal uniformly both the longer hunger rhythms (15 minutes to ij hours) and the more rapid rhythm (30 seconds) of the hunger pangs.