INTESTINAL JUICE AND DIGESTION IN INTESTINE. 181 



with cells of glandular epithelium, showing small but distinctly marked 

 nuclei. The follicles collected round each terminal branch of the main 

 duct are bound together by a thin layer of connective tissue, and covered 

 with a plexus of capillary bloodvessels. 



The follicles of Lieberkiihn, which are much more numerous than the 

 preceding, are not situated in the submucous connective tissue, but 

 occupy the entire thickness of the mucous membrane, forming, like the 

 gastric follicles in the mucous membrane of the stomach, the greater part 

 of its substance. They are 



simple, nearly straight tubules, Fl - 50 - 



from y 1 ^ to T V of a millimetre 

 in diameter, lined throughout 

 with cylindrical epithelium, 

 opening by their orifices upon 

 the free surface of the intes- 

 tinal mucous membrane and 

 terminating below by rounded 

 extremities. They are so 

 thickly set that in many places 

 there appears to be no space 

 left between them, except that 

 occupied by the capillary 

 bloodvessels which encircle 

 them in every direction. 



The fluid produced by the 



mucous membrane of the small testine of Dog. 



intestine consists of a mixture 



of the secretions of these two sets of glands. But as, owing to the situa- 

 tion of Brunner's glands, it has been found impossible to obtain their 

 secretion unmixed with other fluids, and as it is evidently much less 

 abundant than that produced in the remainder of the intestine, the 

 secretion of the follicles of Lieberkiihn is regarded as the main con- 

 stituent of the intestinal juice. It is by no means easy to obtain this 

 fluid in a pure form and in normal condition. There is no single excre- 

 tory duct, like that of the pancreas, into which a canula might be 

 inserted ; and a fistulous opening made in the intestine itself would of 

 course yield a mixture of all the secretions discharged into its cavity. 

 If these should be shut off by a ligature permanently applied above 

 the fistula, the disturbance of the digestive process would be so great, 

 that the experiment could hardly be expected to give a valuable result. 



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

 obtain the intestinal juice in condition sufficiently pure for examination. 

 Bidder and Schmidt first tied the biliary and pancreatic ducts, and then 

 established an intestinal fistula below, from which they extracted the 

 fluids accumulated in the cavity of the gut. Frerichs operated by 

 opening the abdomen, taking out a loop of intestine, emptying it so 

 far as possible by gentle pressure, isolating its cavity by the application 



FOLLICLES OF 



from Small In- 



