DIGESTION IN THE LARGE INTESTINE. 347 



might be carried into the epithelial cells covering a vil- 

 lus. The bile moistening the surface of the villus may 

 facilitate the passage of oil, as it does through a paper 

 filter or a plate of pi aster- of -Paris, and it is also said 

 io stimulate the contractions of the villi; if so, its efficacy 

 in promoting the absorption of fats will be explained, in 

 spite of its chemical inertness with respect to those bodies,* 



Digestion in the Large Intestine. The contractions of 

 the small intestine drive on its continually diminishing 

 contents until they reach the ileo-colic valve, through which 

 they v e ultimately pressed. As a rule, when the mass 

 enters the large intestine its nutritive portions have been 

 almost entirely absorbed, and it consists merely of some 

 water, with the indigestible portion of the food and of the 

 secretions of the alimentary canal. It contains cellulose, 

 elastic tissue, mucin, and somewhat altered bile pigments; 

 commonly some fat if a large quantity has been eaten; and 

 some starch, if raw vegetables have formed part of the diet. 

 In its progress through the large intestine it loses more 

 water, and the digestion of starch and the absorption of 

 fats is continued. Finally the residue, with some excretory 

 matters added to it in the large intestine, collects in the 

 sigmoid flexure of the colon and in the rectum, and is 

 finally sent out of the Body from the latter. 



The Digestion of an Ordinary Meal. We may best sum 

 up the facts stated in this chapter by considering the diges- 

 tion of a coiumon meal; say a breakfast consisting of bread 

 and butter, beefsteak, potatoes and milk. Many of these 

 substances contain several alimentary principles, and, since 

 these are digested in different ways and in different parts 

 of the alimentary tract, the first thing to be done is to con- 

 sider what are the proximate constituents of each. We 

 then separate the materials of the breakfast as in the f olV 

 lowing table 



* Some recent researches make it probable that a good deal of the 

 emulsified fat is also picked up by amoeboid connectjve-tissue cor- 

 puscles, which push their way between the epithelial cells and 

 thrusting processes (p. 20) into the intestine, pick up oil-droplets, 

 and then travel back and convey their load to the lacteal. 



