40 PHYSIOLOGY AND HEALTH. 



canal or its parts, and by this means they aid in carrying 

 the food forward. 



70. The inner lining, called the mucous membrane, se- 

 cretes the slimy mucus with which the whole inner surface 

 of the canal is moistened and protected from any irritating 

 quality of the contents. This membrane is loose and flab- 

 by, and, when the canal is empty and contracted, it is drawn 

 into wrinkles or folds, and seems to be too large for the 

 sack. But when the canal is distended with food, or any 

 other matter, it is drawn out, and lies more smoothly over 

 the inner face of the sack. Besides these folds, which are 

 made in the mucous membrane by the contraction of the 

 canal, there are other folds, which run around the inner 

 surface of the tube crosswise its length. These are perma- 

 nent, whether the tube be contracted or distended. This 

 membrane or lining of the intestine is furnished with a set 

 of glands, which prepare and throw into the canal a pecul- 

 iar fluid called the intestinal juice. This is another coop- 

 erator in the work of digesting the food and fitting it for 

 the blood. It meets and combines with the chyme in this 

 part of the alimentary canal, or the duodenum, and there 

 it digests or changes some of the elements of the food that 

 had not been so changed by the fluids in the stomach. 



71. The pancreas is a large gland lying behind the stom- 

 ach, and performs an important part in the work of digestion. 

 It prepares another fluid, called the pancreatic juice, and 

 sends it through a tube into the upper part of the duodenum. 

 This juice enters into combination with still other elements 

 of the food, especially the oily matters or fats, which had 

 not been affected by the gastric or intestinal juices, and 

 prepares these for the use of the blood. 



72. Thus each of these three different digestive fluids or 

 juices prepared in the stomach, the duodenum, and the 

 pancreas performs its own and peculiar part in the work 

 of digestion. They convert the nutritive elements of the 

 food into a condition fit to enter and become a part of the 

 blood. These elements constitute a milky fluid called chyle, 

 which is yet in the alimentary can il ; but it is destined to 



