92 HUMAN PHYSIOLOGY CHAP. 



little oil. Shake thoroughly for a minute and notice that the oil is 

 changed to a creamy liquid, called an emulsion. Milk is a good 

 example of an emulsion. Lather is an emulsion. 



74. Places of Digestion. We may sum up the places 

 of the digestive changes as follows: (i) In the mouth 

 the foods are cut, ground, and softened, and some of the 

 starchy material is changed into sugar by the action of the 

 saliva. (2) In the stomach a large amount of food may 

 be stored up for digestion, most of the foods are soft- 

 ened by the churning action of the muscles, and some 

 of the proteids are dissolved by the action of the gastric 

 juice. (3) In the small intestine the starchy foods are 

 all converted into sugars, proteids are dissolved, and fats 

 and oils are broken up into small droplets so that they 

 may enter the blood. 



75. Peristalsis. We have learned that the food 

 passes through the oesophagus by a peculiar contrac- 

 tion of the longitudinal and circular muscles to which 

 is given the name peristalsis. The stomach churns the 

 food by constantly throwing it back and forth, now 

 pressing in one direction and now in another. 



In the small intestine there is a muscular movement 

 which thoroughly mixes the foods with the various 

 digestive fluids and also forces the contents along 

 through the winding course of the canal. As the food 

 is thus moved along from the mouth through the various 

 parts of the alimentary canal, its bulk is increased by 

 the addition of saliva, gastric juice, bile, pancreatic 

 juice, and intestinal juice, and it becomes more and more 

 nearly liquid. The only solids found in the chyle are 



