196 FUNCTIONS OF NUTRITION. 



whitish points. Farther down they occur in clusters of several 

 together, and in the lower part of the jejunum and in the ileum they 

 constitute rounded or oval patches, from H to 5 centimetres in length, 

 known as " Peyer's patches." These patches are situated opposite the 

 attachment of the mesentery, with their long diameter parallel to the 

 axis of the intestine. 



The structure of the solitary glandules and of those forming Peyer's 

 patches is the same. 



Each follicle is a rounded or ovoid body, from one-half to two milli- 

 metres in diameter, situated partly in the mucous membrane and partly 

 below it. It consists of a closed capsule, from the inner surface of 

 which slender anastomosing filaments pass through the substance of 

 the organ, forming a scaffolding or frame-work of minute fibres. In 

 the interstices there is a small quantity of fluid, together with an 

 abundance of lymph corpuscles, or faintly granular cells about 13 mmm. 

 in diameter. The follicle is also provided with capillary blood-vessels, 

 which penetrate its investing capsule, inosculate freely in its interior, 

 and return upon themselves in loops near its centre. 



These follicles have a close relation with the lymphatics of the intes- 

 tine. The lymphatic vessels coming from the villi form a plexus in the 

 substance of the mucous membrane, from which branches pass to the 

 follicles and ramify over them, forming another plexus upon their in- 

 vesting capsule. They do not, however, penetrate into the interior 

 of the follicles, which are occupied by blood-vessels alone. Owing to 

 the analogy in structure between these bodies and portions of the 

 lymphatic glands, as well as to the fact that the lacteals from the neigh- 

 borhood of Peyer's patches are more numerous than those from other 

 points of the intestine, the closed follicles are generally regarded as 

 belonging to the system of the lymphatic glands. They furnish no 

 secretion to the intestinal cavity, but are connected in some way with 

 the elaboration of the absorbed materials. 



Absorption by the Villi, 



The villi are the active agents in the process of absorption. The 

 entire mucous membrane of the small intestine, including the valvular 

 conniventes, represents about 6000 square centimetres of surface ; and 

 as the number of the villi is, on the average, not less than 30 to the 

 square millimetre, there must be at least from fifteen to twenty millions 

 of them in tho intestine. By their abundance, as well as by their pro- 

 jecting form, they multiply the extent of contact of the digested fluids 

 with the mucous membrane, and increase, to a corresponding degree, 

 the activity of absorption. They hang out into the nutritious, semi- 

 fluid mass in the intestinal cavity, as the roots of a tree penetrate the 

 soil ; and they imbibe its liquefied portions with a rapidity which is in 

 proportion to their extent of surface and the movement of the circu- 

 lation. 



Absorption is also hastened by the peristaltic action of the intestine. 



