THE DIGESTIVE TRACT OF MAN 369 



Note that all the organs are held in place by a fold of the body- 

 cavity lining called the mesentery. What is its use ? A cream-colored 

 body, the pancreas, can be located between the stomach and the first 

 bend in the small intestine. 



The digestive tract of man. Comparing the food tube of man 

 and its glands part by part with that of the frog, we find a striking 

 similarity as to parts. The lower part of the digestive tube in the 

 frog is relatively much shorter than that of man, whose small in- 

 testine is about 20 feet in length. The large intestine is also rel- 

 atively shorter. We find that in general the uses of the parts are 

 quite similar in spite of their difference in size and the method of life. 



Self-Testing Exercise 



The digestive tract of man consists of a (1), beginning 



at the (2) and ending at the (3). Ducts from several 



(4) which aid in digestion empty into it. The parts of the 



food tube are (5), (6), (7), (8), 



(9) and (10) (11). The largest glands 



are the (12) and (13). 



PROBLEM IV. WHAT DIGESTIVE CHANGES TAKE PLACE IN 

 THE STOMACH? 



Demonstration 3. To determine the conditions most favorable for 

 gastric digestion. 



Use five test tubes or beakers and some boiled white of egg. In the 

 first tube put minced white of egg and water ; in the second minced 

 white of egg and 0.2 per cent hydrochloric acid ; in the third, fourth, 

 and fifth minced white of egg, 0.2 per cent hydrochloric acid, and 

 pepsin. 



Keep the first three in a warm place at about a temperature of 

 blood heat for several hours. Keep the fourth in an ice box or sur- 

 rounded by cracked ice. Keep the fifth in boiling water for 15 or 20 

 minutes, then place it in the warm place with the first, second, and 

 third. 



Test the first with biuret test 1 for the presence of a soluble protein 

 (a peptone). Test the second, third, fourth, and fifth with biuret 

 test and note results. 



1 Biuret solution : To the material to be tested add its own bulk of concentrated 

 caustic soda. Then add a drop or two of weak copper sulphate solution. A 

 violet or blue color shows the presence of unchanged protein, a rose pink the 

 presence of peptone. 



