INTESTINAL DIGESTION 85 



sugar to glucose. It does practically all the work of 

 digesting starch and sugar. 



The third ferment, steapsin, saponifies some of the fat 

 with the soda and potash of the chyme. About one half 

 an ounce of soap is thus formed daily. It acts as a lubri- 

 cating and cleansing agent. The ferment also emulsifies 

 the remainder of the fat. 



117. Action of the bile. About a quart of bile is poured 

 into the intestine each day. It has a slight power in emul- 

 sifying fat, and in converting starch into glucose, but while 

 its direct action is small, it does a great amount of work in 

 helping and stimulating all the processes in the intestine. 

 It almost doubles the power of the pancreatic juice. It 

 acts as a lubricant to enable the food to slip down the 

 intestine easily. It stimulates the peristalsis of the intes- 

 tine, and prevents the growth of germs of fermentation. 

 It also enables digested food to pass more readily from 

 the intestine into the blood tubes. When bile is of poor 

 quality, or too little in quantity, digestion is less perfectly 

 performed, and headaches, mental dullness, and all the 

 symptoms called biliousness result. 



118. Peristalsis. The intestine shows peristaltic move- 

 ments like those in the esophagus. A half an inch or so 

 of muscle fiber, running lengthwise of the intestine, con- 

 tracts, pulling the next lower part of the intestine up over 

 a lump of food. Then the circular fibers contract, squeez- 

 ing the food down the tube, while the fibers next below 

 repeat the process, as the first ring of contraction relaxes. 

 So the contraction runs down the tube, forcing the intestinal 

 contents before it. 



This peristalsis is a slow, gentle movement. By it the intestinal 

 contents are mixed with its juices, and slowly propelled toward the 

 large intestine, where it is propelled still more slowly. 



