Section of both vagi in the chest was made in three dogs, and after this operation observations on the gastric hunger contractions were continued for from two weeks to three months. Observations were'made in some cases two hours after the vagi section.
Section of the vagi leaves the empty stomach on the whole permanently hypotonic; that is, at least for a period of up to three months after the operation. The tonus of the empty stomach in these dogs varies somewhat from day to day, and occasionally the tonus may approach that of a dog with the vagi intact, but on the whole the tonus is permanently much lower than normal. This is evident, not only from the observations by means of the balloon in the gastric cavity, but also on direct inspection and by palpation (introducing the finger through the fistula).
The hunger contractions of the empty stomach are changed mainly in rate and regularity. The duration of each individual contraction is about normal, or on the whole less than normal.
The long-drawn-out contractions or tetanus are rarely seen. But the intervals between the contractions vary on the whole from 2 to s minutes or even up to 8 minutes. The strength, or rather the amplitude, of the individual contractions may appear greater than normal, evidently because the contractions start rather suddenly and without any marked preliminary increase in tonus, and the maximal contractions are evidently so complete that all the air is forced out of the balloon. These contractions may continue of fairly uniform amplitude and rate for 2 to 3 hours, that is, during a whole observation period. The contractions vary in strength and rate from day to day, and on some days they may be completely absent during the entire observation period (2 to 4 hours).
The periodicity of the hunger rhythm is, on the whole, obscured, except on. the days when the gastric tonus approached that in normal dogs. On such days the contractions appear at shorter intervals, and tend to fall into groups similar to those in normal dogs. Periods of gastric hunger contractions of normal rate and intensity have been observed as early as 12 hours after complete section of the vagi in the chest. The period of most powerful hunger contractions so far observed in any dog was recorded in one dog 24 hours after the vagi section. The dog had during the four weeks preceding the vagi section showed almost invariably the type II rhythm. It was therefore a dog with unusually intense gastric motor activity. The complete section of the vagi causes on the whole less depression in dogs that exhibit great hunger contractions while the vagi are intact. The variations in the rate and intensity of the gastric hunger contractions in different dogs are therefore primarily due to individual variations in the condition of the stomach rather than to variations in the central innervation or the central inhibition.
In the dogs with the vagi sectioned, but the splanchnic nerves intact, the "psychic" or reflex inhibition of the gastric hunger contractions is still in evidence, but the inhibition "appears not to be so marked as when the vagi are intact. Accurate comparisons are, however, difficult to make because of the lowered tonus and the usual long intervals between the hunger contractions after section of the vagi. We expected an augmentation of the inhibition through the splanchnics after the vagi section. Instead of finding this to be the case, there actually appeared a gradual diminution in the influence of the splanchnic nerves on the empty stomach in the dog observed for 3 months after section of the vagi. It was not due to the regeneration of the vagi fibers, and consequent restoration of the vagus tonus. If further work should establish this as a fact, we should have a significant instance of physiological readjustment-either an actual diminution in the inhibitory impulses through the splanchnics in consequence of a dynamic readjustment in the central nervous system, or else an increased resistance ("tolerance") to the splanchnic impulses on the part of gastric motor mechanism. It is also evident from this experiment that if adrenalin is a factor in the inhibition of the gastric contractions via the splanchnic nerves, section of the visceral branches of the vagi leads to a decreased output of this substance from the adrenal gland under the influence of the splanchnic nerves.