ALIMENTATION AND DIGESTION 



127 



middleman, in that form which is best fitted for the use 

 of the tissues. 



34. Digestion in the large intestine. The large intestine 

 contains no villi, and its glands secrete an intestinal juice 

 characterized by a large content of mucin (p. 44). 



In the small intestine the amount of water added by secre- 

 tion balances that absorbed, so that the consistency of the 

 contents undergoes but little change from the stomach to the 

 beginning of the large intestine. This consistency, it will be 



FIG. 62. The paths by which the products of digestion enter the general 



circulation 



Those which are absorbed by the blood vessels ((7) of the intestine pass by the 

 portal vein (P. V.) to the liver before they can enter the right auricle (R.A.) through 

 the hepatic vein (H. V.) and the inferior vena cava (I. V.C.). Those products which 

 are absorbed by the lacteals pass directly to the superior vena cava (S.V.C.) 

 through the thoracic duct 



remembered, was (approximately) that of moderately thick 

 pea soup. During the passage through the small intestine 

 the digested portions of the food are being removed by 

 absorption, while the indigestible elements are left behind. 

 Among the indigestible elements of food are certain connec- 

 tive tissues of the animal foods, but especially the cellulose 

 (p. 97), which forms the cell wall of plant tissues. The large 

 intestine receives from the small this indigestible material, 

 together with a certain variable but usually comparatively 

 small proportion of the proteins, fats, and carbohydrates 



