DIGESTION. 



189 



being composed of rounded follicles clustered about a central excretory 

 duct. Each follicle is about T J Q of a millimetre in diameter, and con- 

 of a membranous wall, lined with nucleated cells of glandular epithe- 

 lium. The' follicles collected round each terminal branch of the duct 

 are bound together by a thin layer of 

 connective tissue, and covered with a FIG. 31. 



plexus of capillary blood-vessels. 



The follicles of Lieberkiihn, which are 

 much more numerous than the preced- 

 ing, occupy the entire thickness of the 

 mucous membrane. They are nearly 

 straight tubules, from T J 2 to T ! g of a milli- 

 metre in diameter, lined with cylindrical 

 epithelium, opening on the free surface 

 of the mucous membrane, and terminat- 

 ing below by rounded extremities. They 

 are so thickly set that, for the most part, 

 there appears to be no space between Portion of one of BEER'S GLA.VDS; 

 them, except that occupied by capillary from human intestine, 



blood-vessels. 



The fluid produced by the mucous membrane of the small intes- 

 tine consists of the secretions of these two sets of glands. But owing 

 to the situation of Brunner's glands, their secretion is always mixed 



with other fluids ; and by the 

 intestinal juice proper is under- 

 stood the secretion of Lieber- 

 kiihn's follicles. It is by no 

 means easy to obtain this fluid 

 in pure form and normal con- 

 dition. The follicles have no 

 single excretory duct, in which 

 a canula might be inserted ; and 

 a fistulous opening in the intes- 

 tine would yield a mixture of 

 all the secretions discharged 

 into its cavity. If these should 

 be shut off by a ligature applied 

 above the fistula, the disturb- 

 ance of the digestive process 

 would be so great, that the ex- 



OF LJEBEKKUHN; iroui small intestine 



of dog. penment could hardly be ex- 



pected to give valuable results. 



Nevertheless, attempts have been made, by various methods, to 

 obtain the intestinal juice for examination. Bidder and Schmidt tied 

 the biliary and pancreatic ducts, and then established an intestinal fis- 

 tula below, from which they extracted the fluids accumulated in the 

 gut. Frerichs operated by opening the abdomen, taking out a loop of 



FIG. 32. 



