CH. XXXVII.] INTESTINAL MOVEMENTS 559 



the movements are inhibited for a brief period, after which they are 

 greatly augmented. 



(2) The Sympathetic. These fibres leave the spinal cord by the 

 anterior roots from the sixth thoracic to the first lumbar, pass 

 through the lateral chain, but do not reach their cell-stations until 

 they arrive at the superior mesenteric ganglia : thence they pass as 

 non - medullated, post - ganglionic fibres to the muscular coats. 

 Stimulation of these nerves causes inhibition of any peristaltic 

 movements that may be present. They also contain vaso-motor 

 fibres, and section of these leads to vaso-dilatation and a great 

 increase of very watery succus entericus. 



These two sets of nerves (vagus and sympathetic) terminate in 

 the ganglionated plexus of Auerbach, situated between the two 

 muscular layers of the intestinal wall. 



Under normal circumstances, the intestinal movements are 

 regulated from the central nervous system ma these two channels. 

 Nevertheless, after all the nerves are cut, the movements continue, 

 and may remain normal for months. This independence of control 

 from the central nervous system justifies the use of the term 

 autonomic (see Chapter XVIL). The true peristaltic waves are, 

 however, coordinated reflex actions, the centres for the reflex being 

 situated in the ganglion cells of Auerbach's plexus. The movements 

 entirely cease if the intestine is painted with cocaine, or if nicotine 

 is injected, for under the influence of these drugs the sy nap tic junc- 

 tions of the ganglion cells are paralysed. The importance of the 

 integrity of the plexus was also shown by Magnus in his experiments 

 with strips of intestinal muscle ; such strips are incapable of 

 spontaneous rhythm if the nerve plexus is not removed with them. 

 Yanasi found that the intestinal muscle of the embryo guinea-pig 

 will contract when directly stimulated, but it is only capable of 

 spontaneous peristalsis after the development of Auerbach's 

 plexus. 



In order that peristalsis may attain its object in driving the 

 intestinal contents onwards, it is necessary not only that a wave of 

 contraction should travel along, but a wave of relaxation must also 

 take place in the front of the mass which is urged forwards. This 

 does take place on stimulation ; the normal stimulus is the presence 

 of material within the intestine ; the intestine is usually quiescent 

 when empty. But, as Starling showed, a pinch applied to any 

 particular spot will cause a wave of contraction behind the point 

 pinched, and a wave of relaxation or inhibition in front of it, which 

 travels downwards. 



Peristalsis may be stimulated in many ways, and inhibited in 

 many ways : 



(1) The usual stimulus is doubtless the mechanical one of the 



