404 Our Surroundings 



dicitis. There are no digestive ferments secreted by the glands 

 of the large intestine ; therefore if any digestion occurs, it is due 

 to secretions that pass into it from the small intestine. It is often 

 a breeding place for bacteria that induce fermentation and become 

 a source of danger to the health. 



Absorption. When food has been thoroughly digested and is 

 in soluble form, it is ready to pass through the mucous membranes 

 of the alimentary canal into the blood. The process of this move- 

 ment of the digested food into the blood is known as absorption. 

 Absorption begins in the stomach and is continued in the 

 small intestine. Since only digested food can be absorbed, the 

 amount taken up in the stomach is slight, as only a small portion 

 of food is completely digested there. By far the greater part 

 of absorption takes place in the small intestine. 



The small intestine is well adapted by struc- 

 ture for the absorption of food. It is very long 

 and coiled and its inner lining is covered with 

 numerous small projections, called villi, thus 

 affording a large surface for absorption. These 

 villi, found in no other part of the alimentary 

 canal, contain two kinds of capillaries, blood 

 capillaries and lacteals or lymph capillaries, all 



VILLI OF THE tiny tubes which convey the fluid food to the 

 SMALL INTESTINE blood by tWQ distinct routes> 



Let us first consider the route through the blood capillaries. 

 They carry all non-fatty food, which is absorbed by the process 

 of osmosis from the small intestine through the walls of the 

 villi, and through the walls of the blood capillaries. These many 

 and intricate blood capillaries merge into one tube, called the 

 portal vein. The fluid enters this vein, and is carried to the liver 

 where it undergoes certain changes. 



The fats reach the blood by a different course. They, too, 

 are absorbed in liquid form by the process of osmosis, through 

 the cell walls of the villi. Here they enter the lacteals, which 

 merge into a tube called the thoracic duct. This tube carries the 

 fluid fatty food to a large vein at the base of the neck into which 

 it opens and discharges its contents into the blood current. 



