INTESTINAL DIGESTION 



133 



simple sugars. Some of these enzymes complete the digestion of 

 starch and sugar which was started in the mouth. Another con- 

 stituent, enterokijiase, causes the trypsinogen of pancreatic juice 

 to form trypsin. There is also an active hormone, secretin, in the 

 intestinal juice. It has no digestive action but passes into the 

 blood stream and is carried to the liver and the pancreas, which 

 it activates. (A hormone is a chemical substance formed in one 

 part of the body and activating another part.) It has been 

 found that if a dog is fed and some of its blood in the vein lead- 

 ing from the intestine is introduced into the blood of another 

 dog, the liver in the second dog immediately secretes a large 

 amount of bile, and the pancreas secretes pancreatic juice, which 

 shows that a hormone must have passed through the blood 

 and was carried to the pancreas and the liver. In the human 

 body, most of the food is digested in the small intestine because 

 the food stays there longest. It has been estimated, from obser- 

 vations, that the last food of 

 a meal passes out of the small 

 intestine about ten hours 

 after eating. There are more 

 enzymes in this part of the 

 digestive tract than in any 

 part of the canal, which, also, 

 accounts for the large amount 

 of digestion that occurs here. 

 The large intestine leads 

 from the small intestine. It 

 is about five feet long, and 

 about two and one half inches 

 in its broadest part. A little 

 pouch is formed where the large intestine connects with the small 

 intestine. Leading from this pouch is a short, narrow, wormlike 

 tube, usually less than the diameter of an ordinary lead pencil, 



intestine* 



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vermi/orin-. 



Enough of the small intestine and large intes- 

 tine are shown to make clear the position of the 

 appendix. Note the opening of the appendix. 



