266 ELEMENTARY PHYSIOLOGY less. 



the remains of the food, now consisting either of un- 

 (ligestible material, or of material which has escaped the 

 action of the several digestive juices, or withstood their 

 influence, gradually assume the characters of fteces. 



17. Absorption from the Intestines.— A great deal 

 of the absorption takes place in the small intestine 

 (though the process is continued on in the large intestine), 

 and there can be no doubt that it is largely effected by 

 means of the villi. Each villus, as we have seen (p. 257), 

 is covered by a layer of epithelium, and contains iti the 

 centre a lacteal radicle, between which and the epithelium 

 lies a network of capillary blood-vessels embedded in a 

 delicate tissue. The soap and fatty acids pass into the 

 cells of the epithelium where they reunite with glycerine 

 to form droplets of fat which travel past the capillary 

 blood-vessels, into the central lacteal radicle ; so that, 

 after a fatty meal, these lacteal radicles of the villi become 

 filled with fat. The lacteal radicle is continuous with the 

 interior of the lymphatic vessels which ramify in the walls 

 of the intestine, and which pass into the large lymphatic 

 vessels running along the mesentery towards the thoracic 

 duct. Into these vessels the finely divided fat passes from 

 the lacteal radicle of the villus, and, mixing with the 

 ordinary lymph contained in the vessels, gives their 

 contents a white, milky appearance. Lymph thus white 

 and milky from the admixture of a large quantity of finely 

 divided fat is called chyle ; and this white chyle may after 

 a meal be ti'aced along the lymphatics of the mesentery 

 to the thoracic duct, and along the whole course of that 

 vessel to its junction with the venous system. After a 

 meal, in fact, this vessel is continually pouring into the 

 blood a large quantity of chyle, i.e. of lymph made white 

 and milky by the admixture of fats drawn from the villi 

 of the small intestine. 



In the case of the proteins and carbohydrates, the 

 result of digestion has been to produce a solution of 

 nitrogenous organic acids and sugars which are extremely 



