88 HUMAN PHYSIOLOGY CHAP. 



gastric juice and its action on the various foods. Similar 

 observations have been made in other cases since. 



Get a few grains of pure pepsin from the drug store and make 

 some artificial gastric juice by mixing together one grain of pure 

 pepsin, four tablespoonfuls of warm water, and about ten drops of 

 strong hydrochloric acid. Label it gastric juice. It is now ready 

 for use. 



1 . Put some gastric juice into a small bottle or test tube and add 

 soft-boiled egg. Watch carefully for ten or fifteen minutes. 



2. Repeat, using a few fibers of raw beefsteak. Notice carefully 

 what happens. 



3. Repeat, using still other proteid foods. What do you learn 

 from these experiments ? 



73. Intestinal Digestion. The portion of the ali- 

 mentary canal into which the foods pass from the 



stomach is called the intes- 

 tines. The intestines begin at 

 the smaller and lower end of 

 the stomach at the right side 

 and form the remainder of the 



FlG. 40. Small intestine cut -,. ,. , -, ,-,-,, r 



open to show the folds of the digestive tube. The first por- 

 mucous membrane. (Drawn tion or small intestine is about 



by Mater.) _c / j / 



twenty- five feet long and one 



inch in diameter, while the second or large intestine is 

 about five feet long and two inches in diameter. The 

 intestines consist of an outer, thin serous coat, of a 

 middle, muscular coat having two layers of fibers (the 

 longitudinal and the circular), and of an inner, very 

 heavy lining of mucous membrane. The entire wall 

 varies in thickness from one sixteenth to one eighth of an 

 inch. The tube is very much coiled up in the abdomen, 



