DIGESTION 



207 



the pancreatic external secretion need no special description; indeed, 

 little that is definite and certain could be said about them. 



INTESTINAL JUICE, or succus entericus, as it used to be called, is even 

 less known than is pancreatic juice because it is secreted in very small 

 quantity and becomes immediately mixed with the complex liquid com- 

 pounded by the salivary glands, the stomach, the liver, and the pancreas. 

 This juice is opalescent, straw-colored, strongly alkaline, with a specific 

 gravity of about 1010, and contains much proteid, mucin, carbonate, 

 and lactate. It is produced by the simple follicles, crypts of Lieberkiihn 

 of the small intestine, and perhaps in part also by Brunner's glands. 

 The function of the intestinal juice appears to be to hydrolyze carbohy- 

 drates, to finish the hydrolysis of protein, and to invert sugars. It probably 

 puts the finishing touches to the hydrolysis of carbohydrates preparatory 

 to inverting them as they pass through the intestinal wall during absorp- 

 tion. As inverting enzymes, invertase (inverting saccharose to dextrose) 

 and maltase (inverting maltose to dextrose) have been named. The 

 proteolytic ferment present, according to Abderhalden, is erepsin. 



FIG. 105 



L.Ct 



Section in the bottom end of a tubular gland of a dog's duodenum: a, b, c, "protoplasmic" 

 cells; rf, e, mucous cells. (Bizzozero.) 



Whether the enzyme enterokinase, described by Bayliss and Starling as of 

 such great importance for stimulating in union with secretin the pan- 

 creatic glands, is produced by the simple follicles or by Brunner's glands 

 is undecided. Delezenne thinks it is secreted by the lymph-follicles, and 

 Camus supposes that it is confined to the gut's lumen, while, on the other 

 hand, the non-enzymic secretin may go directly into the blood-stream. 

 In either event enterokinase would form a part of the intestinal juice, 

 and in its supposed function of developing trypsinogen into trypsin 

 would have considerable importance. 



BILE has some proper influence on the intestinal digestion of fats 

 as has been just suggested above, but the action, although perhaps 

 important, is none too well understood. 



