THE SMALL INTESTINE. 



169 



In structure the solitary nodules correspond to lymph-nodules in other 

 localities, consisting of a capsule of fibrous tissue enclosing the delicate reticu- 

 lum which supports the lymphocytes within its meshes. Within the larger 

 nodules, spherical or ellip- 

 soidal germ -centres are 

 present; they are, how- 

 ever, not constant, being 

 present, as a rule, in young 

 subjects, but often absent 

 in older ones. Each nod- 

 ule is surrounded by a rich 

 network of small blood- 

 vessels, from which fine 

 capillaries penetrate the 

 lymphoid mass (Fig. 151). 

 Definite lymph-paths are 

 absent within the nodules, 

 although a plexus of lym- 

 phatics surrounds their 



exterior. 



FIG. 210. Surface view of mucous membrane of small intes- 

 tine (ileum), showing villi, glands and solitary lymph-nodules. 

 Xio. 



The aggregated nod- 

 ules or Peyer's patches 

 are collections of simple 

 nodules, the individual nodules being blended by intervening lymphoid tissue 

 (Fig. 2 1 1 ). They are present in the lower half of the small intestine, especially 

 in the ileum, but exceptionally are found as high as the beginning of the 

 jejunum. The patches appear as slightly raised elongated oval areas. They 



Submucosa supporting mucosa 



, 

 x.- -.. 



FIG. 2ii. Transverse section of ileum, showing a Peyer's patch cut across. X 8. 



usually number about thirty, although as few as eighteen or as many as eighty 

 have been counted. Their length is ordinarily from 1-4 cm. and their breadth 

 from 6-1 6 mm. f Each patch contains from 20-30 ovoid individual lymph- 

 nodules which, when well developed, occupy both the mucous and submucous 

 coats, their smaller ends almost reaching the epithelium and their bases the 

 muscular tunic. The villi and crypts of Lieberkiihn are present over the 

 areas between the nodules, although less developed than beyond the patch. 



