290 ANATOMY FOR NURSES [Chap. XV 



taking food in and moving it along through the digestive canal, 

 and (2) in separating the food into small particles upon which 

 the digestive fluids can act rapidly. These processes consist of : — 



1. Mastication. 



2. Deglutition. 



3. Peristaltic action of oesophagus. 



4. Peristaltic action of stomach. 



5. ^Movements of the intestines. 



6. Defecation. 



Chemical digestion. — Chemical digestion is a process of hy- 

 drolysis which is dependent upon the presence of enzymes. By the 

 term hydrolysis is meant the breaking down of complex molecules 

 into simpler ones with the absorption of water. An example of 

 hydrolysis is the conversion of any of the complex sugars into 

 simpler sugars. (See page 8.) In the disaccharids only one 

 splitting is necessary, as each molecule of a complex sugar plus one 

 molecule of water will give two molecules of a simple sugar which 

 is soluble and read>' for absorption. The starches are more com- 

 plex in their composition, hence they must pass through several 

 stages of decomposition before they are changed by hydrolysis 

 to a simple sugar. Each splitting of the molecule gives substances 

 with simpler composition, though with the same relative proportion 

 of the constituents, and to each such substance produced is given 

 a special name. The proteins are even more complex than the 

 starches, and pass through a greater number of stages in the 

 process of digestion. The substances formed in each stage are of 

 lighter molecular weight and are named (1) meta-proteins, (2) pro- 

 teoses, (3) peptones, (4) polypeptids, and (5) amino-acids. 

 Many physiologists are of the opinion that protein digestion does 

 not pass beyond the peptone stage, as peptones are soluble and 

 can be absorbed. 



Fats are hydrolyzed and split up into fatty acids and glycerine; 

 the fatty acids are then acted upon by the bile and pancreatic 

 juice, and form soap. (See page 298.) 



Cause of chemical digestion. — It is possible to make carbo- 

 hydrates, proteins, and fats undergo the same changes outside 

 the body as occur during digestion. Carbohydrates, proteins, 

 and fats, if boiled with a mineral acid or subjected to the action 

 of enzA'mes, will hydrolyze and split up into simpler substances. 



