Chap. XIV] THE DIGESTIVE SYSTEM 269 



(a) Solitary lymph nodules. — Closely connected with the lym- 

 phatic vessels in the walls of the intestines are small, rounded 

 bodies of the size of a small pin's head, called solitary lymph 

 nodules. These bodies consist of a rounded mass of fine lym- 

 phoid tissue, the meshes of which are crowded with leucocytes. 

 Into this mass of tissue one or more small arteries enter and form 

 a capillary network, from which the blood is carried away by 

 one or more small veins. Surrounding the mass are lymph 

 channels which are continuous with the lymphatic vessels in the 

 tissue below. 



Aggregated lymph nodules. — They are simply collections of 

 lymph nodules, commonly called Peyer's patches. A well-formed 

 Peyer's patch consists of fifty or more of these solitary lymph 

 nodules, arranged in a single 

 layer, close under the epithe- 

 lium of the intestinal mucous 

 membrane, and stretching 

 well down into the tissue be- 

 neath. These patches are 

 circular or oval in shape, 

 from one-half to three inches 

 (12.5-75 mm.) long, and one- 

 half inch (12.5 mm.) wide, 

 and from twenty to thirty in 



number TheV are lartrest ^^^- 156. — - Aggregated Lymph Nodule 



"^ . ^ /■ (Peyer's Patch). (Gerrish.) 



and most numerous in the 



ileum. They increase in size during digestion. These Peyer's 

 patches are the seat of local inflammation and ulceration in 

 typhoid fever. It is interesting to note that in this condition, 

 the long axis of the ulcer runs in the same direction as the long 

 axis of the intestine ; whereas in tuberculosis of the intestine, 

 the long axis of the ulcer is at right angles to the long axis of the 

 intestines. 



Function. — It is in the small intestine that the greatest amount 

 of digestion and absorption takes place. The valvulae conniventes 

 delay the food so that it is more thoroughly subjected to the action 

 of the digestive juices ; and being covered with villi they increase 

 the surface for absorption. The glands of the small intestine 

 secrete the succus entericus which aids in the digestion of food. 



