338 HUMAN PHYSIOLOGY 



Absorption in Stomach. — Fluids leave the stomach more rapidly 

 than do solids, milk, for example, taking about two hours to digest, 

 while a meal of meat and vegetables will not leave the stomach 

 for three to four hours. It is not thought that any great amount 

 of absorption of digested food occurs through the wall of the 

 stomach. As soon as food reaches the small intestine, however, 

 sugars and peptones are slowly absorbed, and pass into the blood. 



The Intestine and Glands connected with it. Laboratory Work on the Frog} 

 — The liver is the most prominent structure found in the body cavity. 

 Note its position, its red color, the number of lobes into which it is divided. 

 If the liver be pushed to one side, the small intestine is found to occupy part 

 of the remaining space in the body cavity. Between the stomach and a 

 coil of the small intestine lies a pinkish gland, the 'pancreas. The duct 

 or tube which carries its secretion empties, together with the bile duct from 

 the liver, into the small intestine, a short distance posterior to where the 

 latter leaves the stomach. Find the greenish gall bladder which holds the 

 secretion of the liver, the bile. Try to trace the course of the bile duct to 

 the small intestine. Notice the abrupt change in the diameter of the food 

 tube near its posterior end where it forms the large intestine; the latter 

 empties into a space called the cloaca. This forms a common outlet for 

 the food tube, kidneys, and reproductive organs. 



Position and Structure of the Pancreas. — In man, the pancreas 

 occupies the same relative position that it does in the frog. The gland is a 

 rather diffuse structure; its duct empties in a common opening with the 

 bile duct, a short distance below the pylorus. In internal structure, the 

 pancreas resembles the salivary glands. The fluid, as we shall see, has some 

 functions possessed by the saliva. 



The following experiments may be performed to illustrate the process of 

 digestion by pancreatic fluid. The several enzymes of pancreatic fluid are 

 sold in a powdered form as a substance called pancreatin.^ An artificial 

 pancreatic fluid may be prepared by adding to some pancreatin enough 

 water to dissolve it. To show saponification of fats add ten volumes of 1 .5 

 per cent sodium carbonate. 



Experiments to show the Properties of Pancreatic Fluid. — Prepare (1) test 

 tube containing starch and artificial pancreatic fluid; (2) test tube con- 

 taining proteid and artificial pancreatic fluid; (3) test tube containing oil 

 and artificial pancreatic fluid 4- ten volumes of 1 .5 per cent sodium carbonate ; 

 (4) test tube containing oil and water. Place tubes 1 and 2 in a pan con- 

 taining warm water. Leave at a temperature of 98° Fahrenheit, if possible, 

 for twelve hours. Then test No. 1 with Fehling's solution; No. 2 for pep- 

 tone with the biuret test. Test the contents of tube No. 1 or No. 2 with 

 red litmus paper. What reaction do j'-ou obtain? Shake up No. 3 and 

 No. 4 an equal number of times; compare the color and appearance of the 

 two tubes one minute after shaking. Note that the milky condition existing 



' In the female frog it will be necessary to remove the ovary, filled with tiny black 

 and white eggs, and the oviducts, twisted tubes through which the eggs are passed 

 to the outside of the body, before working on the rest of the digestive tract. 



2 This substance must be bought from a reliable firm, as it is frequently adulterated. 



