Removal of the cerebral hemispheres in the guinea-pig leads to somewhat increased gastric tonus and hunger contractions (Dr. King). In the pigeon this operation does not change the hunger contractions of the empty crop, except that visual and auditory stimuli do not lead to inhibition of these movements in the decerebrated bird (Rogers). In frogs removal of the cerebrum has no effect on the hunger contractions of the stomach (Patterson). Goltz's decerebrated dog showed hunger. We may therefore conclude that in so far as the stomach hunger contractions are dependent upon tonus and motor nervous impulses via the vagi nerves, these impulses do not originate in the cerebral hemispheres.
In man (infants as well as adults) the gastric hunger contractions are at least as frequent and intense during sleep at night as during the waking state. In our five days' starvation experiment continuous records of the stomach contractions were taken during sleep at night. These records show that the stomach was in strong tonus and hunger contractions practically half of the time of sleeping. The hunger periods were less frequent during the day when the subject was about his work.
Numerous experiments on dogs show that the hunger contractions and the gastric tonus are more vigorous and regular when the animal is sleeping than when he is awake and taking notice of things about him. The only apparent exception to this condition so far observed in any species is the rumen of the goat. A few observations on one goat seemed to show that the hunger contractions of the rumen or first stomach pouch decrease in intensity when the animal is lying down sleeping. We shall not be satisfied that this is so until the same result is obtained on a number of ruminants. Possibly the gastric motor part of the vagi nervous apparatus in the ruminating animals is under a more direct control from the cerebrum than is the case in other species.
During sleep there is decreased activity of the central nervous system in general; decreased tonus of the skeletal muscles; decreased tonus of the musculature of the blood vessels, at least in certain parts of the vascular system; decreased tonus of the urinary bladder, etc.; in short, a lowered activity of all the neuromuscular mechanisms so far investigated. One might have expected that so far as the tonus of the empty stomach depends on a central influence by way of the vagi the gastric tonus and hunger contractions would be diminished during sleep. But instead of being depressed in sleep the hunger contractions continue with the same vigor as during the waking state, and in many instances with increased vigor. The increase in the gastric hunger contractions during sleep may be due to the elimination of all inhibitory impulses via the splanchnic nerves. But the absence of depression certainly indicates that the vagogastric tonus mechanism, at least in man and dog, occupies a unique position in the organism-a degree of independence of afferent impulses (extero-ceptors) and central processes not known in the case of any other neuromuscular apparatus.