DIGESTION. 109 



INTESTINAL DIGESTION. 



The process of digestion as it takes place in the small intestine is 

 exceedingly important and complex, and is brought about by the 

 action of the pancreatic juice, the bile, and the intestinal juice. 



The contents of the stomach at the close of gastric digestion con- 

 sist of water, inorganic salts, peptones, undigested albumins and 

 starches, maltose, cane-sugar, liquefied fats, cellulose, and the indi- 

 gestible portions of meats, cereals, fruits, etc. This so-called chyme 

 is quite acid in reaction, and upon its passage through the now open 

 pylorus into the intestine it excites a reflex stimulation and secretion 

 of the intestinal fluids, which are decidedly alkaline in reaction, and 

 which have a neutralizing action on the chyme. As soon as the latter 

 becomes alkaline and gastric digestion is arrested, the various phases 

 ot intestinal digestion begin which eventuate in the transformation 

 of all the remaining undigested nutritive materials into absorbable 

 and assimilable compounds. 



The small intestine is about 22 feet in length and about i H inches 

 in diameter. Like the stomach, it possesses three coats, as follows : 



1. The serous, or peritoneal. 



2. The muscular, the fibers of which are arranged for the most part 

 circularly. Some of the fibers are so arranged as to form longi- 

 tudinal bands. 



3. The mucous, which presents a series of transverse folds, known as 

 the valvula conniventes. 



Intestinal Glands. In that portion of the small intestine known 

 as the duodenum are to be found a number of small, branched, tubu- 

 lar glands (Brunner's), the acini of which are lined by short, 

 cylindric cells, similar to those lining the pyloric glands. From the 

 duodenum to the termination of the intestine the mucous membrane 

 contains an enormous number of tubular glands (Lieberkuhn's), 

 formed by an inversion of the basement membrane and lined by 

 epithelial cells. The common secretion of these intestinal glands 

 forms the intestinal juice. This is a thin, opalescent, slightly yel- 

 lowish fluid, alkaline in reaction, and contains water, salts and pro- 

 teid matter. 



The function of the intestinal juice is but incompletely known. 

 It appears to have the power of converting starch into dextrose ; 

 It is doubtful whether it is capable of digesting either albumins or 



