THE INTESTINES 357 



acid is present. Again, the food coming to the stomach is alkaline, 

 from the saliva it contains; the acid neutralizes this (cf. 220). Since 

 food is exposed to the air before we eat it, it contains a multitude of 

 bacteria, including those of fermentation. The acid destroys these, 

 and thus prevents fermentation and infection. We must not, however, 

 depend upon the hydrochloric acid to destroy all bacteria, for some, 

 such as those of typhoid, are not killed by it. 



The action of the gastric juice changes food to a milky substance 

 called chyme; this is ready for digestion in the intestines. 



365. The Intestines. As portions of food are changed 

 to chyme, the muscular ring at the pylorus is relaxed, and 

 the chyme enters the small intestine. Both the intestines 

 together form a tube about 27 or 28 feet long. This tube 

 is so long that it must be coiled in the abdomen (cf. 

 Fig. 273, 350) . Herbivorous animals have even longer in- 

 testines; that of the grown ox is about 150 feet long (cf. 

 345). In man the small intestine is about 22 feet long 

 and 1 irich in diameter; the large intestine is about 2 

 inches in diameter. Both of these have lengthwise and 

 circular muscles, like those of the esophagus. 



Three glands discharge their secretions into the small 

 intestine; the glands are the intestinal glands (which 

 secrete the intestinal juice), the liver, and the pancreas. 

 All of these secretions have an alkaline reaction, and thus 

 differ from the gastric juice, which has an acid reaction. 



The organs that are of the greatest importance in 

 absorbing the digested food of the small intestine, and in 

 transferring nutriment from the alimentary canal to the 

 blood, are the villi (singular, villus). These are small 

 elevations that project from the wall of the small intestine, 

 and make its absorbing surface about 6 or 7 times as 



