264 HANDBOOK OF PHYSIOLOGY. 



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

 which consists largely of Peyer's glands be injected with blue by press- 

 ing the point of a fine syringe into one of the lymphatic sinuses, the 

 Peyer's glands will appear as grayish-white spaces surrounded by blue ; 

 if now the arteries of the same be injected with red, the grayish 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 communicate 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. 191, 196, 198, and 199), are confined ex- 



Fio. 195. Transverse section of Injected Peyer's glands (from Kolliker). The drawing was 

 taken from a preparation made by Frey: it represents the fine capillary- looped network spreading 

 from the surrounding blood-vessels into the interior of three of Peyer's capsules from the intestine 

 of the rabbit. 



clusively to the mucous membrane of the small intestine. They are mi- 

 nute 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- 

 tine, and at forty to seventy in the same area at the lower part. They 

 vary in form even in the same animal, and differ according as the lym- 

 phatic vessels they contain are empty or full of chyle; being usually, in 

 the former case, flat and pointed at their summits, in the latter cylindri- 

 cal or cleavate. 



Each villus consists of a small projection of mucous membrane, and 

 its interior is therefore supported throughout by fine adenoid tissue, 

 which forms the framework or stroma in which the other constituents 

 are contained. 



