DIGESTION AND ABSORPTION 



359 



in that organ. Contrary to common belief, the greatest amount of food is 

 digested after it leaves the stomach. But this organ keeps the food in it 

 in almost constant motion for a considerable time, a meal of meat and 

 vegetables remaining in the stomach for three or four hours. While 

 movement is taking place, the gastric juice acts upon proteids, softening 

 them, while the constant churning movement tends to separate the bits 

 of food into finer particles. Ultimately the semifluid food, most of it still 

 undigested, is allowed to pass in small amounts through the pyloric valve, 

 into the small intestines. This is done by the expansion of the ringlike 

 muscles of the pylorus. 



The partly digested food in the small intestine almost immediately 

 comes in contact with fluids from two glands, the liver and pancreas. We 

 shall first consider the function of the pancreas. 



Position and Structure of the Pancreas. The most impor- 

 tant digestive gland in the human body is the pancreas. 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. 





Appearance of milk under the microscope, showing the natural grouping of the 

 fat globules. In the circle a single group is highly magnified. Milk is one form 

 of an emulsion. (S. M. Babcock, Wis. Bui. No. 61.) 



Starch added to artificial pancreatic fluid and kept at blood heat 

 is soon changed to sugar. Proteid, under the same conditions, is 

 changed to peptone. Fats, which so far have been unchanged 

 except to be melted by the heat of the body, are changed by the 

 action of the pancreas into a form which can pass through the 

 walls of the food tube. If we test pancreatic fluid, we find it strongly 



