Complete sections of the splanchnic and vagi nerves were made on four dogs and observations made on the gastric hunger contractions for 30 to 60 days after the operation. The sections of the splanchnic nerves were made 7 days after the section of the vagi. After this complete isolation of the dog's stomach from the central nervous system, there is practically a permanent hypotonus of the stomach except under conditions of prolonged starvation. The gastric hunger contractions are much the same as when the vagi alone are severed. The contractions are usually of great amplitude, but the intervals between the contractions are frequently longer than in normal dogs. The grouping of the contractions in periods is usually in evidence. These contractions of the isolated and empty stomach were present 10 to 20 hours after the vagi section, and there was some improvement in the rhythm or an approach toward the normal tonus and contraction rate during the 30 to 60 days of observation. On the whole, the hunger contractions of the isolated stomach conform to type I. The type II is rare except during prolonged starvation. Short periods (2 to 3 minutes) of incomplete tetanus are frequently seen, especially during prolonged starvation, and during the first half of the hunger period. It is therefore clear that all the essential characteristics of the hunger contractions of the empty stomach are determined by the local gastric mechanisms rather than by the character of the central innervation or the central inhibition.
Cannon has reported observations on the effects of vagi and splanchnic section on the gastric movements of digestion in cats. Section of the splanchnic nerves did not affect the movements of digestion; section of the vagi caused slowing and weakening of the peristalsis of digestion, but the normal rate of peristalsis was practically restored in a few days. Combined vagi and splanchnic section left the digestive movements of the stomach practically normal, even shortly after the operation. It seems that section of the vagi or complete section of the vagi and the splanchnic nerves in dogs causes on the whole a greater change in the movements of the empty stomach than does the same lesion in cats in case of the / movements of the filled stomach. This probably means that the tonus of the vagi plays a greater r61e in the movements of the empty than in the movements of the filled stomach. For it is not likely that there is such marked difference in the relative importance of the vagi nerves in cats and dogs.
The changes in the character of the gastric hunger contractions after isolation of the stomach from the central nervous system seem primarily due to the persistent hypotonus. This is indicated by the fact that on days when the stomach of a normal dog shows relatively slight tonus the hunger contractions approach the type shown by the isolated stomach, and on days when the isolated stomach exhibits tonus approaching that in normal dogs the hunger contractions tend to assume the normal type. Occasionally records are obtained from the empty and isolated stomach that practically demonstrate the above point. During a period of relatively slow hunger rhythm the tonus for some unknown reason may increase markedly for periods of varying length, and during these periods the hunger contractions are identical in rate and character with those of the intact stomach in normal (strong) tonus. In one of the dogs with the vagi and splanchnic nerves sectioned six days of fasting led to the appearance of periods of very great gastric tonus, and during these periods (virtually periods of incomplete tetanus) the gastric contractions assumed the form of type III.
However, the details of the changes in the hunger rhythm after isolation of the stomach from the central nervous system seem of minor importance in this connection. The essential point is that since the empty stomach, completely isolated from the central nervous system, does exhibit the typical hunger contractions, the primary rdle of the gastric nerves is that of modifying or regulating essentially automatic mechanisms in the stomach wall. In other words, the extrinsic nerves to the stomach play a rdle similar to that of the nerves to the heart in the regulation of the heart rhythm. Further analysis of the hunger mechanism must be directed primarily to the intrinsic neuromuscular apparatus of the stomach, and secondarily to the factors that control the vagus tonus.