CHAPTER XIV 

 SALIVARY AND GASTRIC DIGESTION 



Before food is placed in the mouth it has, in many 

 cases, undergone some changes which anticipate those 

 which the digestive enzymes are now to carry forward. 

 Many industrial and domestic processes have helped 

 to separate the useful from the useless and to subdivide 

 the food. This is true of the milling of grain. The 

 ripening of fruits and vegetables and the analogous 

 change in meat those are in the line with digestion and 

 so far as they have advanced they lighten the task which 

 remains to be accomplished. 



Mastication. In the mouth a vigorous mechanical 

 treatment is administered to the food. The lower jaw 

 has a complex movement, up and down, forward and 

 back, and from side to side. As a result of this the food 

 is not merely shaved and sliced (the particular work of 

 the front teeth with their chisel form) but rubbed and 

 ground between the uneven surfaces of the molars. 

 The tongue contributes much to the process of mastica- 

 tion, rubbing portions of the food against the roof of the 

 mouth and constantly altering the position and bearing 

 of those parts on which the teeth are actively at work. 



The Saliva. While the mechanical operation goes 

 on the saliva flows from the ducts of the glands in quan- 

 tities of which we have little conception. The secre- 

 tion forms a very large share of what we swallow and 

 so of the stomach contents after a meal. It has been 

 estimated that 3 pints of saliva are produced in a day. 

 The discharge is of a reflex nature but is best placed 

 among those reactions favored by certain states of 

 consciousness which have been called psycho-reflexes. 



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