"^ ABSORPTION. 17 



' . . /*• " "^»»t 



which secrete a juice known as the si^c'cus entericusj 



' which probably seconds the pancreatic juice. The digested 

 material is in part absorbed into the blood, and the mass of 

 food still being digested is passed along the small intestine by 

 means of the muscular contractions of the walls, known as 

 peristaltic action. It reaches the large intestine, and its 



^reaction is now distinctly acid by reason of the acid fer- 

 mentation of the contents. The walls of the large intestine 



. contain glands similar to those of the small intestine, and 

 the digestive processes are completed, while absorption also 

 goes on ; so that by the time the mass has reached the 

 rectum, it is semi-solid, and is known as fasces. These 

 contain all the indigestible and undigested remnants of the 

 food and the useless products of the chemical digestive' 

 processes. 



So far, we have dealt with the general process of diges- 

 tion, that is, the preparing the food for absorption into 

 the blood ; we shall now sketch the manner of absorption, 

 and the treatment of the absorbed matters after they have 

 reached the blood. Absorption begins in the stomach by 

 direct osmosis into the capillaries or fine branches of blood- 

 vessels in its walls, and a similar absorption, especially of 

 water, takes place along the whole of the digestive tract. 

 But lining the intestines there are special hair-like projec- 

 tions called villi ; they contain capillaries belonging to the 

 Dortal system (blood-vessels going to the liver), and small 

 Je^ls known ""aslacteals coTmected with lymph spaces in 

 fce~wall_gfjhe intestine. T he lacteals lead into a longi- 

 tud inai ly mp h vesseT'o r thoracic duct, wlncli "enters one of 

 Ite* veins' ||3f°"m e necK /^ 111 TEe" centre of each villus the 



bacteals ellM Hi DUhd spaces ; round them is a netted tissue 

 with many lymph spaces ; round these a capillary network 

 of blood-vessels, and also some muscular fibres used for 

 shortening and- emptying the villus. The whole is enclosed 

 in a sheath of fine skin or epithelium. The finely divided 

 fat passes through this epithelium into the lymph spaces of 

 the netted tissue, then into the lacteals, and so to the tlMracic 



^uct. ' ^ ■ 



The villus empties itself by Ihe contraction of its muscular fibres ; on 

 the relaxation of these, the fat is prevented from returnnig. by valves, 

 while the expansion sucks the fat from the netted tissue. l^Ttie thoracic 



rning.' 1 



