236 



INTESTINAL DIGESTION. 



dissecting the muscular coat from the mucous membrane, they may be seen 

 with the naked eye, in the areolar tissue, in the form of little, rounded bod- 

 ies, about one-tenth of an inch (2-5 mm.) in diameter. Examined micro- 

 scopically, these bodies are found to consist of a large number of rounded 

 follicles held together by a few fibres of connective tissue. They have blood- 

 vessels ramifying on their exterior and are lined with glandular epithelium. 

 They communicate with an excretory duct which penetrates the mucous mem- 

 brane and opens into the intestinal cavity When these structures are ex- 

 amined in a perfectly fresh preparation, the excretory duct is frequently 

 found to contain a clear, viscid mucus, of an alkaline reaction. This secre- 

 tion has never been obtained in quantity sufficient to admit of the determi- 

 nation of its chemical or physiological properties. Its quantity must be very 

 small, compared with the secretion produced by the follicles of Lieberkiihn. 



The intestinal tubules, or follicles of Lieberkiihn, the most important 

 glandular structures in the intestinal mucous membrane, are found through- 



Fio. 68. Intestinal tubules ; magnified 100 diameters (Sappey). 



A. From the dog. 1, excretory canal ; 2. 2, primary branches ; 3, 3, secondary branches ; 4, 4, terminal 



culs-df-sac. 



B. From the ox. 1, excretory canal ; 2, principal branch dividing into two ; 3, branch undivided ; 4, 4, 



terminal culs-de-sac. 



C. From the sheep. 1, trunk ; 2, 2, branches. 



D. Single tube, from the pig. 



E. From the rabbit and hare. 1, simple gland ; 2, 3, 4, bifld glands ; 5, compound gland from the 



duodenum. 



out the whole of the small and large intestines. In examining a thin section 

 of the mucous membrane, these little tubes are seen closely packed together, 



