ABSORPTION. 



somewhat wavy line, toward the base of the villus, and then be- 

 comes continuous with a small twig of the mesenteric lacteals. 



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

 their projecting form, and their great abundance, they increase enor- 

 mously the extent of surface over which the digested fluids come 

 in contact with the intestinal mucous membrane, and increase, also, 

 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 

 their circulation. 



The process of absorption is also hastened by the peristaltic 

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

 parts of the alimentary canal, is double, consisting of both circular 

 and longitudinal fibres. The action of these fibres may be readily 

 seen by pinching the exposed intestine with the blades of a forceps. 

 A contraction then takes place at the spot irritated, by which the 

 intestine is reduced in diameter, its cavity obliterated, and its con- 

 tents forced onward into the succeeding portion of the alimentary 

 canal. The local contraction then propagates itself to the neighbor- 

 ing parts, while the portion originally contracted becomes relaxed ; 

 so that a slow, continuous, creeping motion of the intestine is pro- 

 duced, by successive waves of contraction and relaxation, which 

 follow each other from above downward. At the same time, the 

 longitudinal fibres have a similar alternating action, drawing the 

 narrowed portions of intestine up and down, as they successively 

 enter into contraction, or become relaxed in the intervals. The effect 

 of the whole is to produce a peculiar, writhing, worm-like, or 

 "vermicular" motion, among the different coils of intestine. During 

 life, the vermicular or peristaltic motion of the intestine is excited 

 by the presence of food undergoing digestion. By its action, the 

 substances which pass from the stomach into the intestine are 

 steadily carried from above downward, so as to traverse the entire 

 length of the small intestine, and to come in contact successively 

 with the whole extent of its mucous membrane. During this pas- 

 sage, the absorption of the digested food is constantly going on. 

 Its liquefied portions are taken up by the villi of the mucous mem- 

 brane, and successively disappear ; so that, at the termination of the 

 small intestine, there remains only the undigestible portion of the 

 food, together with the refuse of the intestinal secretions. These 



