DIGESTION. 259 



forming lymph-follicles. In the condition in which they have been most 

 commonly examined, each gland appears as a circular opaque-white 

 rounded body, from ^ to -^ inch in diameter, according to the degree in 

 which it is developed. They are principally contained in the submucous 

 coat, but sometimes project through the muscularis mucosce into the 

 "mucous membrane. In the agminate glands, each follicle reaches the 

 free surface of the intestine, and is covered with columnar epithelium. 

 Each gland is surrounded by the openings of Lieberkuhn's follicles. 



The adjacent glands of a Peyer's patch are connected together by ade- 

 noid tissue. Sometimes the lymphoid tissue reaches the free surface, 

 replacing the epithelium, as is also the case with some of the lymphoid 

 follicles of the tonsil (p. 236). 



Fever's glands are surrounded by lymphatic sinuses which do not 

 penetrate into their interior; the interior is, however, traversed by a very 

 rich blood capillary plexus. If the vermiform appendix of a rabbit, which 

 consists largely of Peyer's glands, be injected with blue, by pressing the 



FIG. 189. Agminate follicles, or Peyer's patch, in a state of distension, x 5. (Boehm.) 



point of a fine syringe into one of the lymphatic sinuses, the Peyer's 

 glands will appear as greyish white spaces surrounded by blue; if now the 

 arteries of the same be injected with red, the greyish patches will change 

 to red, thus proving that they are surrounded by lymphatic spaces, but 

 penetrated by blood-vessels. The lacteals passing out of the villi commu- 

 nicate with the lymph sinuses round Peyer's glands. 



It is to be noted that they are largest and most prominent in children 

 and young persons. 



Villi. The Villi (Figs. 183, 188, 190, and 191), are confined exclu- 

 sively to the mucous membrane of the small intestine. They are minute 

 vascular processes, from a quarter of a line to a line and two-thirds in 

 length, covering the surface of the mucous membrane, and giving it a 

 peculiar velvety, fleecy appearance. Krause estimates them at fifty to 

 ninety in number in a square line, at the upper part of the small intes- 



