DIGESTION 227 



A loop or coil of small intestine may be so distended by gas or 

 ingesta as to become twisted, but it is more difficult to imagine 

 either of these conditions producing twist or displacement of the 

 large intestines, and it becomes a question, as we have previously 

 said, how far the action of the muscular bands of the bowel may- 

 have a contributing influence. That great force is necessary is 

 undoubted, bearing in mind the difficulty, if not impossibility, of 

 restoring the parts to their position post mortem, or endeavouring 

 after death to reproduce the lesions experimentally. These 

 matters will be referred to again. 



Nervous Mechanism of the Intestinal Canal. — Two distinct 

 impulses are conveyed by the intestinal nerves — viz., those for 

 contraction and for inhibition. In the anterior part of the tract 

 the former function is mainly or entirely carried out by the vagus, 

 stimulation of which is found to cause active contraction of the 

 small intestines. Contraction of the large intestines is effected 

 through branches of nerves which issue from the sacral portion of 

 the cord, and pass with the nervi erigentes to the hypogastric 

 plexus. From this plexus fibres run in the coats of the large 

 intestines, producing on stimulation much the same results as the 

 vagus — viz., active contraction of both circular and longitudinal 

 coats. 



Stimulation of certain branches of the sympathetic nerve stops 

 or inhibits the contractions produced by stimulation of the 

 vagus, hence the term ' inhibitory.' The inhibitory nerves of 

 the small intestine are derived from the dorso-lumbar portion of 

 the cord, pass by the rami communicantes (re, Fig. 80) to the 

 main sympathetic chain, Sy., and thence through the large 

 and small splanchnic nerves to the solar plexus, from which the 

 final distribution to the intestines is made. The inhibitory fibres 

 for the large intestines are derived mainly from the lumbar cord 

 through re. and Sy. (Fig. 80) to the inferior mesenteric ganglion. 

 From this ganglion inhibitory fibres are supplied to both longi- 

 tudinal and circular coats. The connections of the abdominal 

 sympathetic ganglia of the horse are shown in Fig. 81. 



Contractions of the bowels and peristalsis can occur after all 

 nerves leading to the intestines have been divided ; this points to 

 the existence of local ganglia, and such may be found in the 

 intestinal wall. The intestinal movements are automatic and 

 self-regulated, though they can be provoked by both chemical 

 and mechanical stimuli. The normal stimulus to peristalsis is 

 the passage of ingesta along the canal. In the dog even the sight 

 of food is said to promote peristalsis. Gases, such as C0 2 , H 2 S, 

 and CH 4 , and organic acids, such as acetic, propionic, caprylic, 

 etc., act as stimuli, and promote contraction, which is a fortunate 



