ABSORPTION. 191 



penetrated by capillary bloodvessels, which pass through its investing 

 capsule from without, inosculate freely with each other in its interior, 

 and return upon themselves in loops near its centre. 



The follicles have a close relation with the lymphatics of the intestine. 

 The lymphatic vessels coming from the villosities form a plexus in the 

 substance of the mucous membrane from which branches pass to the 

 follicles and ramify upon their surface, forming another close plexus upon 

 their investing capsule. The lymphatic vessels, however, do not pene- 

 trate 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 coming from the neighborhood of Peyer's patches are 

 more numerous than from other points of the intestine, the closed folli- , 

 cles are generally regarded as belonging to the system of the lym- i-- 

 phatic glands. They constitute the simplest form of these glands, 

 situated in or immediately beneath the intestinal mucous membrane. 

 They furnish no fluid secretion to the intestinal cavity, but are con- 

 nected in some way with the preparation or elaboration of the absorbed 

 materials. 



Mechanism of Absorption by the Villi. The villi are the active 

 agents in the process of absorption. The entire extent of the mucous 

 membrane of the small intestine, including the valvulse conniventes, is 

 estimated at 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 the whole length of the small intestine. By their great abundance, 

 accordingly, as well as by their projecting form, they multiply the ex- 

 tent of surface over which the digested fluids come in contact with the 

 intestinal mucous membrane, and increase, to a corresponding degree, 

 the energy with which absorption takes place* They hang out into the 

 nutritious, semi-fluid mass contained in the intestinal cavity, as the 

 roots of a tree penetrate the soil ; and they imbibe the liquefied portions 

 of the food with a rapidity which is in direct proportion to their extent 

 of surface and the activity of the circulation. 



The process of absorption is also hastened by the peristaltic move- 

 ments of the intestine. The muscular layer here, as in other parts of 

 the alimentary canal, is double, consisting of both circular and longitu- I/ 

 dinal fibres. The action of these fibres maybe readily seen by pinching 

 the exposed intestine with the blades of a forceps. A contraction takes 

 place at the spot irritated, by which the intestine is reduced in diame- 

 ter, its cavity partially obliterated, and its contents forced onward into 

 the succeeding portion of the alimentary canal. The local contraction 

 then propagates itself to the neighboring parts, while the portion 

 originally contracted becomes relaxed ; so that a slow, continuous, 

 creeping motion of the intestine is produced, by successive waves of 

 contraction and relaxation, which follow each other from above down- 

 ward. At the same time, the longitudinal fibres have a similar alter- 



