Section 3. 

 Intestinal Digestion. 



The chyme which is poured from the stomach into the small 

 intestines meets there with three digestive fluids — viz., the 

 succus entericus, the .bile, and the pancreatic juice. 



The Succus Entericus is prepared by the glands of the small 

 intestines ; in the duodenum the glands of Brunner are found, 

 while the follicles of Lieberkiihn are met with throughout the 

 whole of the small and large intestines. Lieberkuhn's crypts 

 supply a considerable proportion of intestinal juice, while the 

 secretion from the glands of Brunner is scanty. Brunner's 

 glands, which are very large in the horse, are arranged on the 

 same principle as the gastric glands, while those of Lieberkuhn are 

 tubular glands, amongst the cylindrical epithelial cells of which 

 numerous mucus-forming goblet cells may be found. 



The total amount of succus entericus secreted by the horse is 

 given by Colin as 10 litres (17 pints). 



At one time it was considered that the succus entericus was a 

 comparatively unimportant fluid, the chief function of which 

 was to neutralise the acid chyme ; Colin, however, showed that 

 in the horse it has a distinctly digestive effect. It is now known 

 that though a pure secretion of Lieberkuhn's crypts has little or 

 no digestive action excepting on starch, an extract of, and juice 

 squeezed from the intestinal wall has a most important function. 

 The Lieberkuhn fluid is quantitatively small in amount, and 

 alkaline in reaction due to carbonate of soda. The intestinal 

 extract, on the other hand, contains three enzymes, and in 

 addition a peculiar chemical substance of remarkable properties. 

 The enzymes are : 



1. Enterokinase, which converts the trypsinogen, the mother 

 substance of the pancreatic proteolytic enzyme, into trypsin. 



2. Erepsin, a proteolytic ferment, which supplements the 

 work of trypsin, acting on deutero-albumoses and peptones, 

 breaking them up into amido-acids and hexone bases. 



3. Inverting Ferments, converting double sugars which cannot 

 be utilised by the tissues into single sugars which can. Of 

 inverting ferments there are three : 



Maltase, converting maltose and dextrin into dextrose. 

 Invertase, converting cane sugar into dextrose and levulose. 

 Lactase, converting milk sugar into dextrose and galactose. 

 Finally, the intestinal fluid contains secretin, which is not a 



