92 STUDIES IN PHYSIOLOGY 



shaking the tubes and by leaving them in a warm place. 

 At the end of several hours, the egg in test tube No. 4, 

 which was treated with all the ingredients of gastric juice, 

 is found to be dissolved, but the pieces remain practically 

 unchanged in ^Jie other tubes. We infer therefore that the 

 proteid of egg is digested by the combined action of pepsin, 

 hydrochloric acid, and water. 



An instructive experiment may be performed in a fifth 

 test tube by adding the three ingredients of gastric juice to 

 a large piece of egg. It will be found that a much longer 

 time is required to digest the egg in this condition. Hence, 

 we see that if food is not properly chewed, the stomach is 

 compelled to ck) a considerable amount of extra work. 



One might ask the interesting question, Why does not 

 the stomach digest itself ? When we eat a piece of tripe, 

 which is prepared from the walls of a cow's stomach, the 

 tripe is liquefied by our gastric juice. Why, then, does not 

 our gastric juice dissolve the walls of our stomach? All 

 we know is that in some unknown way our stomach tissues 

 when alive are able to resist this solvent action. 



8. THE SMALL INTESTINE 



Position and Size. The small intestine is a much coiled 

 tube, filling the larger portion of the abdominal cavity (see 

 Fig. 23). It is usually twenty feet or more in length, and 

 therefore constitutes nearly four fifths of the whole length 

 of the alimentary canal. Beginning at the pyloric end of the 

 stomach with a diameter of about two inche^ it decreases 

 somewhat in size until it opens into the large intestine. 



Peritoneum. The whole abdominal cavity is lined with 

 a thin, smooth membrane called per-i-to-ne'um (Greek peri 

 = around -f- teinein = to extend). Sheets of peritoneum like- 

 wise inclose the various organs found in the abdominal 

 cavity, and connect these organs with the wall of the ab- 

 domen. Per-i-to-ni'tis is an inflammation of any portion of 

 this membrane. To the thin sheets of connective tissue and 



