The question of the nervous control of the gastric hunger mechanism embraces several important physiological problems, none of which are as yet completely solved.
1. On the motor side we have the possibility of actual initiation of the gastric hunger contractions through the motor fibers in the vagi nerves by impulses from cerebral as well as lower centers acting on the motor nuclei of the vagi in the medulla. Even if contractions are not actually caused in this manner, it can be shown that they are in part dependent on a "tonus" influence exerted on the stomach by the vagi nerves. Hence the control of the J vagus tonus becomes a question of paramount importance in the I physiology and pathology of hunger.
2. On the afferent or sensory side we must determine the central paths of the afferent gastric nerves in order to elucidate the genesis of the conscious hunger sensation as well as the conscious and subconscious reflexes evoked by these afferent impulses. This raises the question of the sensory hunger center in the cerebrum. ^
3. We have also to deal with the very important reflex control of the gastric hunger mechanism as well as of the nervous foci in the medulla, mid-brain, and cerebrum concerned in the conduction of sensory and motor hunger impulses.
4. And, lastly, we must consider the automatic or reflex elements in the gastric hunger mechanism itself, independent of all central nervous system control. An understanding of these several factors is of particular importance for the interpretation and the control of the changes in hunger and appetite that we meet in disease.