DIGESTION IN THE DUODENUM. 421 



digestion, are absorbed into the portal and lymphatic systems ; 

 whilst the undigested portions of the food and various excre- 

 tions are further acted on by the bowel, and become the faeces. 



Just as the acid gastric juice was stimulated to flow by the 

 alkaline reaction of the insalivated food, so the three great 

 alkaline secretions entering the intestine are stimulated to flow 

 by the acid chyme. Moderate acidity of the contents, as they 

 enter the duodenum, is manifestly the most favourable to intes- 

 tinal digestion, excessive acidity tending to neutralise the alka- 

 line fluids, and render them inert. 



The nervous mechanism which regulates each of the three 

 secretions is comparatively obscure ; but they appear to be 

 governed, like the gastric functions, both by local ganglia and 

 by centres in the medulla, between which and the viscera there 

 pass the vagus and sympathetic, as afferent and efferent, nerves. 

 The vessels of the parts, so far as is known, are dilated during 

 functional activity. The muscular movements are still, as in 

 the stomach, partly progressive and partly churning, but the 

 former decidedly preponderate. 



II. PHARMACODYNAMICS. 



In pursuing the contents of the alimentary canal from the 

 stomach into the duodenum, the pharmacologist becomes 

 conscious of a decided loss of control over them when they 

 have passed the pylorus. The chyme is now practically beyond 

 recall upwards by vomiting ; and the chemical or physiological 

 effects which could be produced by drugs in the mouth and 

 stomach can only be imperfectly copied in the intestines. Yet 

 a closer examination of the influences on duodenal digestion 

 which are in our power is reassuring. 



The food can be modified in any direction we may think fit, 

 and the proportion of fatty and starchy principles specially ar- 

 ranged to affect intestinal digestion ; or the liver, pancreas, and 

 duodenal glands may be allowed to enjoy physiological rest by 

 abstinence from food. The food may be specially cooked in 

 combination with an extract of pancreas and an alkali, and thus 

 thoroughly "peptonised" or pancreatised before it is taken. 

 Starch may be partly converted into maltose and dextrin 

 Extract of Malt or maltine. If evacuation of the duodenum by the 

 mouth be practically impossible, we may expel its contents down- 

 wards by the use of purgatives, which will be presently studied. 



A more complex problem meets us when we attempt to 

 affect the secretions of the liver, pancreas, and intestinal glands. 

 We cannot directly increase the alkalinity of the secretions, as 

 we increase the acidity of the gastric juice by a dose of 

 diluted hydrochloric acid after meals ; for any alkali given 



