Standing or walking in situ has no effect on the gastric tonus or the hunger contractions. But running in situ promptly inhibits the hunger contractions. The degree and duration of the inhibition are on the whole directly proportional to the speed of the running. In some cases walking seemed to prolong a hunger period without changing the rate or intensity of the individual contractions. In no case did walking or running induce hunger contractions in the quiescent stomach. The results on man are thus identical with the results on dogs. In both species rapid running is accompanied by inhibition of the gastric tonus and hunger contractions. In the case of the dog running in the treadmill, one cannot be sure that the exercise is strictly voluntary and enjoyable. The inhibition may therefore be due to certain emotional states (anxiety, discomfort, mild anger, or fear). This possibility is eliminated by the tests on man. In the men the conditions of the emotions when running in place were not different from that when standing or walking in place. In no case was the running carried to the point of respiratory, cardiac, or muscular distress.
Moderate exercise in the form of playing tennis or walking 4 to 8 miles was taken in the afternoon. No supper was taken, and the motor condition of the empty stomach was recorded from 8:00 p.m. to 12:00 midnight.
//The tracings obtained on the days specific exercise was taken * ■ show on the whole greater gastric hunger activity than the controls. The periods of quiescence become shorter. This tends to make the gastric hunger contractions more or less continuous, and there appears to be some increase in the rate of the contractions. A typical experiment (S. J. O.) may be cited in the way of illustration.
Record of control day.-Lunch 1130 p.m. No special exercise. No supper. Period of observation 8:00 p.m to 12 midnight.
8:00 to 10:00 p.m. Stomach practically quiescent. 10:00 to 10:40. Strong hunger contractions, ending in tetanus. 1 o: 40 to 11:35. Stomach quiescent.
11:35 to 12:05. Moderate hunger contractions ending in tetanus.
Record of exercise day.-Lunch 1:30 p.m. No supper. Tennis 4:00 to 5:00 p.m.; walking 6:00 to 7:00 p.m. Period of observation 8:00 p.m. to 12 midnight.
8:15 to 9:50 p.m. Practically continuous hunger contraction ending in strong tetanus. 9:50 to 10:20. Stomach quiescent.
10:20 to 11:4c Strong hunger contractions ending in tetanus.
(Control day, 70 minutes; exercise day, 190 minutes.) Total duration of hunger periods from 8:00 p.m. to 12 midnight.
In some instances there was no marked difference between records of the control and the exercise days. This is to be expected, since the activity of the gastric hunger mechanism depends in part on factors not understood or controlled. Exercise that brings on a degree of fatigue bordering on exhaustion seems to depress the gastric hunger mechanism. But our experiments on this point are as yet too few to permit a final conclusion.
The immediate effect of stimulation of the cold nerve-endings of the skin by ice pack, alcohol bath, cold shower bath, or cooled air is inhibition of the gastric tonus and hunger contractions, and the degree of inhibition is proportional to the intensity of the stimulation. In no instance did we observe an initial increase in gastric tonus and hunger contractions. When the stimulation is continued the inhibitory effects gradually diminish, even though the man shivers intensely from the cold. In this way the gastric hunger contractions may return to their normal rate, intensity, and regularity, while the man is shivering and jerking like a dog in mild parathyroid tetany. It may be noted in this connection that'mild and in some instances fairly severe parathyroid tetany in dogs does not appreciably influence the gastric hunger contractions.
Intense stimulation of the heat nerve-endings of the skin (hot shower) produces practically the same initial inhibition as the corresponding stimulation of the cold nerve-endings.
While it is true that on prolonged stimulation of the cold nerve-endings of the skin, during a period of gastric hunger contractions, the inhibitory effects gradually disappear, so that the contractions reappear in their normal intensity, these contractions are always felt as weaker than the normal, or may not be felt at all. Evidently the intense sensation of cold dominates consciousness to the exclusion of the gastric hunger pangs.
It is well known that strong stimulation of the cold nerve- • endings of the skin causes a reflex increase of tonus of the urinary bladder. In several instances we started these stomach tests on the men at a time when their bladders were known to contain 50 to 200 c.c. of urine. This permitted us to compare the reflex effect of cold on the stomach and bladder tonus without a balloon in the bladder. When the cold stimulation began during a period of gastric quiescence and was continued long enough to induce intense shivering, a strong desire to micturate soon developed while there was no evidence of increased gastric tonus. Prolonged cold stimulation may produce so great a tonus of the bladder that micturition cannot be inhibited voluntarily. The tonus centers of the urinary bladder are, the vagogastric tonus centers are not, directly influenced by cold stimulation of the skin.
When the cold nerve-endings of the skin are stimulated, as described above, during a period of quiescence of the empty stomach, the stomach remains quiescent. If there is any change in the gastric tonus it is in the direction of inhibition. Nevertheless, this cold stimulation, if not sufficiently intense to be painful, seemed to induce a "sensation of emptiness" in the abdominal region, a sensation that seemed to be associated with appetite and desire for food. We record this with some hesitation, for this sensation of emptiness may be purely subjective (auto-suggestion). It may also be due to the increased tonus of the abdominal muscles. In any event this sensation is clearly different from the hunger pangs.
All of the tests in this group were made on one man (A. j. C). A prolonged cold bath, from 6:00 to 7:00 a.m., followed by a brisk walk, nearly always resulted in increased hunger activity of the stomach as recorded for the period 8:00 a.m. to 12:00 m. The temperature of the water varied from 50 C. to 150 C. The subject remained in the water as long as was deemed safe (10 to 20 minutes) despite discomfort and pain. Water at this temperature soon brings on shivering, contracture, and at times severe headache, and it requires much vigorous exercise to restore the feeling of warmth. Rubbing the skin (rough towel) seems to be of little avail. A typical experiment may be cited in illustration.
Control record.-No bath or breakfast. Observation period 8:00 a.m. to 12:00 m.
8:50 to 10:00 a.m. 26 fairly strong hunger contractions; no tetanus. 11:00 to 11:45. 22 fairly strong hunger contractions; no tetanus.
Gastric tonus on the average 5 cm. bromoform. Test period.-6:00 to 6:15 a.m., cold bath (temperature of water 10° C). No breakfast. Observation period 8:00 a.m. to 12:00 m.
8:00 to 9:00 a.m. 32 strong contractions; no tetanus. 9:45 to 10:25. 23 fairly strong contractions; no tetanus. 11:15 to 11:45. J9 strong contractions ending in tetanus.
Gastric tonus on the average 8 cm. bromoform. Control period.-48 hunger pangs; no tetanus. Test period.-74 hunger pangs; tetanus.
Under ordinary conditions the periods of gastric hunger contractions of the author do not end in tetanus, but the hunger tetanus appears after 3 to 4 days' complete starvation. Intense stimulation of the cold nerve-endings for 15 to 30 minutes thus seems to bring about a condition similar to prolonged starvation. This is in harmony with the observation of Lusk that such stimulation quickly renders the liver free from glycogen. This effect of cold on the gastric hunger mechanism is obviously an indirect one, or brought about through changes in the blood, and is not a direct reflex from the skin.
Lusk has shown that intense cold leads to quicker and more complete oxidation of the body glycogen than prolonged starvation. And it is interesting to note that the same stimulus causes not only an increase in the gastric hunger contractions, but also an even greater increase in the subjective hunger and appetite sensations, probably owing to an increased excitability of the central nervous system. The increased desire to eat after a cold bath, in the case of the healthy individual, is a universal experience. I have investigated this matter in the case of young children, with whom habit or intelligence cannot be assigned as the cause for seeking food after a cold bath. It was found that young children react in the same way as adults.
While these observations include only two species (man, dog), it docs not seem likely that the gastric vagotonus mechanism will have different reflex associations in other animals. But this opinion should not stand in the way of actual investigation of the condition in other vertebrates as well as in the invertebrates. In man and in dogs the situation appears to be this: The vagus motor nuclei in the medulla control, in part, the tonus and hunger contractions of the stomach. The tonus of the vagus nuclei, in turn, are controlled by the condition of the blood rather than by afferent nervous impulses, unless sensory impulses from the stomach musculature itself play such a r61e. This possibility is now under investigation.