80 DIGESTION. 



CHAPTER VI. 

 DIGESTION. 



TJw Principal Processes of Nutrition The General Plan of Digestion 

 Mastication Tlie Teeth Preservation of the Teeth Insalivation 

 The Stomach and tlte Gastric Juice The Movements of tlie 

 Stomach Gastric Digestion The Intestines TJie Bile and Pan- 

 creatic Juice Intestinal Digestion Absorption by means of Blood- 

 vessels and Lacteals Tlie Lymphatic or Absorbent System The 

 Lymph Conditions which affect Digestion The Quality, Quan- 

 tity, and Temperature of Hie Food The Influence of Exercise and 

 Sleep. 



1. Nutrition. The great design of food is to give 

 nutriments nourishment to the body. But this is not 

 accomplished directly, as the food must first pass through 

 certain preparatory changes, as follows : (1), Digestion, by 

 which the food is reduced to a soluble condition; (2), Ab- 

 sorption, by which, when digested, it is imbibed into the 

 blood; (3), Circulation, which carries the enriched blood 

 to the various parts of the system; and (4), Assimilation. 

 by which each tissue derives from the blood the materials 

 necessary for its support. 



2. By these means the sustaining power of food is grad- 

 ually developed and employed, and the vital machinery 

 kept in working order, somewhat after the manner of the 

 steam-engine. To operate the latter, the force imprisoned 

 within the coal and water is set free and converted into 

 motion by the combustion of the fuel and the vaporization 

 of the water. It will be seen, however, when we come to 

 study these operations in the human body, that they are 

 conducted silently and harmoniously, with marvellous deli- 

 cacy and completeness, and without that friction, and con- 



1 . Design of food ? How accomplished ? 



2. Sustaining power of food ? Simile of the engine ? Operation in the human 

 body ? 



