234 FIRST YEAR SCIENCE 



it, and the whole process of digestion is greatly retarded. 

 Thus much more energy is expended than otherwise would 

 be. The saliva is necessary to digest some of the starch 

 and to aid in the further digestion. 



The food passes from the mouth down the throat and 

 through a valve into the stomach. This is a large pouch 

 which will hold usually from three to four pints. It has 

 muscular walls which enable it to contract and expand, 

 thus keeping the food moving about so that it is thoroughly 

 mixed with the gastric juice. The gastric juice is secreted 

 by little glands thickly imbedded in the lining of the 

 stomach. Artificial gastric juice was made in Experi- 

 ment 117. Some of the proteins (Experiment 119) are 

 digested in the stomach, although the larger part of 

 digestion takes place in the small intestine. 



From the stomach the food passes through a valve into 

 the small intestine. This is a complexly coiled tube which 

 fills the larger part of the abdomen. The inner wall of 

 the tube is lined with glands which secrete digestive juices, 

 and into the intestine are poured the secretions from two 

 large glands, the pancreas and the liver. The small 

 intestine is the great digestive organ of the body. Here 

 the fats and oils (Experiment 120) are digested and the 

 digestion of the starches and proteins is completed. The 

 small intestine opens through a valve into the large in- 

 testine^ a tube five or six feet long decreasing in size 

 toward the exit to the body. There is little digestion in 

 the large intestine. 



The changes that take place in the food as it passes 

 through the alimentary canal are very complex, but dur- 

 ing its progress the valuable part of the food is so changed 

 and prepared that it can be absorbed by the blood and 

 transported by it to the different parts of the body where 

 its energy is needed. Absorption takes place all along 



