332 MECHANISMS OF THE DIGESTIVE TRACT 



of the vagus has no apparent effect on the intestines. Bunch 1 only 

 observed an effect (inhibition) once in a large number of experiments, 

 and hence denied that the vagus is to be regarded as a motor nerve. 

 Jacobi 2 states that in the rabbit (after a few days' starvation) stimula- 

 tion of the vagus is without effect, unless the splanchnics or the fibres 

 which run from the suprarenals to the solar plexus be divided, and 

 hence regards these fibres and the vagi as mutually antagonistic. In 

 rabbits he describes the intestinal fibres as conveyed chiefly in one vagus, 

 either right or left, while the other sends fibres chiefly to the stomach. 

 These discordant results are due to the influence of various disturbing 

 factors, among which may be mentioned the influence of anaesthetics and 

 the exposure and handling of the intestines, with the circulatory changes 

 thereby induced. More important than these, however, are the in- 

 hibitory influences to which every part of the intestine is subject, either 

 originating in the higher parts of the gut, and travelling down the 



Fig. 187.— Curves obtained by balloon method, to show effects of exciting peripheral end 

 of right vagus. Upper curve = intestinal contractions, second curve = arterial blood 

 pressure, third curve = excitation marker, lowest curve — time marking in six-second 

 intervals. During the period shown on the excitation marker, the vagus was 

 excited with strong induced currents (tenth excitation). 



intestinal wall, or started by any sensory stimulation of the gut itself, 

 and transmitted reflexly through the spinal cord. It is necessary, there- 

 fore, to cut out such influences as much as possible, by dividing both 

 splanchnics and by avoiding any lesion of the intestine above the 

 observed point, such as a ligature, which might set up descending 

 inhibitory impulses. If these precautions are observed, stimulation of 

 the vagus in the neck, after paralysis of the cardio-inhibitory fibres by 

 means of atropin, will always produce an effect upon the intestinal 

 movements; the effect, which may be little marked at first, but increases 

 with each succeeding stimulation, is twofold — (1) An inhibition with 

 very short latent period (less than one second), leading to the dropping 

 of one or two beats, and (2) an augmentation of the rhythmic contrac- 

 tions, which gradually develops after the lapse of 10 to 30 seconds, and 

 lasts for some length of time after the cessation of the stimulus. The 



1 Journ. Physiol., Cambridge and London, 1897, vol. xxii. p. 357. (This contains an 

 excellent summary of previous work on intestinal innervation, with full references.) 



2 Arch. f. exper. Path. u. Pharmakol., Leipzig, 1892, Bd. xxix. S. 171. 



