On the Effects of Afferent Stimulation of the Vagus upon Some Vegetative Organs

Abstract

1. The centripetal stimulation of the vagus, if comparatively strong, brings pressor effect and if comparatively weak, depressor effect on the blood pressure.
But, in an animal, whose splanchnics are severed or whose abdominal viscera are removed, a strong afferent stimulation of the vagus gives rise rather to a lowering, not to a raising, of the blood pressure.
Also in an animal deeply anaesthetized, the blood pressure is markedly lessened by a strong afferent stimulation. In one with its vagi on both sides cut the result is the same.
Even when the large brain is removed, so far as the medulla oblongata is preserved, the afferent stimulation produces a pressor effect.
2. The afferent stimulation, regardless of its intensity, lessens the rate of heart beat. An increase is rarely observed.
3. Respiration is depressed by the stimulation of the central vagus stump.
4. The automatic movement of the stomach and intestines is more or less inhibited by a relatively strong stimulation of the central vagus stump and is accelerated by a relatively weak stimulation.
5. Changes in blood pressure, rate of heart beat, respiration and movement of the stomach and intestines due to afferent vagus stimulation are similar to those caused by sensory nerve stimulation, with regard to the fact that they show themselves in opposite ways according to whether the stimulation is strong or weak and to the evidences shown in the experiments of anaesthesia, decerebration, etc. It may, therefore, be presumed that the change brought about by the stimulation of the central vagus stump is a reflex phenomenon similar to that due to the sensory nerve stimulation.