DIGESTION AND FOOD. 41 



nourish the whole body, and must first pass into and through 

 the blocd-vessels. 



73. The mucous membrane, or inner lining of the intes- 

 tinal canal, is soft, like velvet, and filled with myriads of 

 pores, which perform an important part of the work of di- 

 gestion. These numberless little pores, or tubes, have their 

 open mouths upon the inner surface of the intestinal canal. 

 They run from the inner channel outward through the walls 

 of this canal. Their mouths are so small as to be invisible, 

 except by aid of a powerful microscope ; and yet they are so 

 numerous as to cover over all the inner surface of this organ. 

 Their duty is to absorb, or suck up, some of the nutritious 

 portion of the digested food, which, when it is in these little 

 tubes, has the appearance of milk. These are, therefore, 

 called the lacteal absorbents. These tubes, -when they first 

 start from the inside of the canal, are almost inconceivably 

 small, but they unite together, two and two, and more, and 

 thus become fewer and larger. The larger tubes again unite, 

 and form other and still larger ones, until they all are joined 

 in one large tube, called the thoracic lacteal duct. This goes 

 along the inner side of the back-bone, from the abdomen to 

 the upper part of the chest, and opens into the great vein, at 

 the right side of the heart. These mouths and tubes, small 

 and large, and this duct, constitute what is called the lacteal 

 system. Its object is to carry the nutritious portion of the 

 chyme from the digestive organs to the blood-vessels. 



74. Beside these lacteal absorbents there is another set 

 of vessels that assist in doing the same work in the lining 

 membrane of the intestinal canal. These are myriads of 

 veins, as minute as the lacteals. They absorb ether 

 portions of the digested food, and carry it through their 

 minute tubes into larger channels, and these pour their 

 contents finally into the great vein near the heart. 



75. In the duodenum, or the upper portion of the intes- 

 tinal canal, the digested food is divided into two kinds 

 that which is to enter the blood-vessels, and the waste. 



4* 



