108 INTESTINAL MOVEMENTS . 



Intestinal movements are dependent on the ganglia of 

 Auerbach's plexus, situated between the outer longitudinal 

 and inner circular layers of muscle. Secretion is believed 

 to be influenced by Meissner's plexus, lying in the sub- 

 mucous coat ; but these ganglia, immediately regulating 

 intestinal movements and secretions, are controlled by 

 cerebro-spinal centres and nerves, notably by the vagi, 

 which, when irritated, cause increased peristalsis, and by 

 the splanchnics, which diminish intestinal movements. 

 The blood-supply of the intestine is mainly regulated by 

 the splanchnics and vagi, but also in part by the lumbar 

 portion of the cord. 



Purgatives vary in the degree and method of their action. 

 The purgative oils, such as linseed and castor oils, act in 

 virtue of their fatty acids, linoleic and ricinoleic acids, set 

 free on saponification in the duodenum. These acids mildly 

 irritate the bowel and so increase peristalsis gently and 

 without griping. Their mechanical lubricant effects assist 

 this action throughout the alimentary tract. 



Another group of purgatives are the anthracene group, 

 all derivatives of anthraquinone. They include aloes, 

 rhubarb, and senna, cause moderate purgation by increasing 

 peristalsis, but do not inflame the bowel wall to any extent. 



The drastics are much more irritant, and cause inflamma- 

 tion of the intestine with the outpouring of considerable 

 inflammatory exudate. In consequence of this condition, 

 absorption is prevented, peristalsis is very violent, and 

 severe purgation, often with griping, follows. 



The last group of agents are those which act by stimu- 

 lating the unstriped muscle in the bowel wall to contraction. 

 These are exemplified by physostigmine and barium, and 

 their action is produced whether given by the mouth or by 

 hypodermic or intravenous injection. 



Purgatives are frequently classified clinically as follows : 



Laxatives or aperients, such as small doses of oil, mag- 

 nesia, sulphur and treacle, with fruits, roots, and green 

 vegetable food. 



Simple purgatives, such as full doses of oils, aloes, various 

 species of rhamnus, which produce more copious, softened, 

 or fluid evacuations. 



