DIGESTION 259 



(2) Peristaltic movements which propel the contents 

 of the gut downwards, every such movement consisting 

 in a contraction of the gut above the point of stimulation 

 and relaxation of it below that point (Starling's 'Law of 

 the Intestines ') 



The peristaltic contractions are the result of a local 

 nerve mechanism (Auer bach's plexus), but they are also, 

 apparently, under the influence of the central nervous 

 system, especially through the medium of the splanchnics, 



f& iu**ik* ^L 



/. 



\ 



FIG. 17. DIAGRAM OF SEGMENTATION IN HUMAN SMALL INTESTINES 

 OCCURRING SIMULTANEOUSLY WITH PERISTALSIS. (HERTZ.) 



which appear to exert a slight tonic inhibition of them. 

 Thus paralysis of the solar plexus induces an exaggerated 

 peristalsis with diarrhoea, and ' nervous diarrhoea ' is 

 probably brought about in this way. On the other hand, 

 irritation of the splanchnics induces colic and constipa- 

 tion, as happens in lead-poisoning or in cases of intra- 

 abdominal inflammation.* 



* See Largiel Lavastine, abst. in Archiv /. VerdauungskranTch., 

 1903, ix. 417. 



172 



