MOUTH DIGESTION. 169 



into this canal, are the salivary glands, the liver, and the pan- 

 creas. 



The digestive process is subdivided into three parts : That 

 which takes place in the mouth mouth digestion; that which 

 takes place in the stomach stomach or gastric digestion ; and that 

 which takes place in the small intestine intestinal digestion. For- 

 merly, when digestion was spoken of it was always stomach diges- 

 tion which was referred to, because it was supposed that the entire 

 process took place in that organ ; and when digestion was impaired 

 the remedies which physicians employed were directed to the 

 stomach alone. There is, unfortunately, too much of this kind 

 of practice even now ; but the study of physiology has taught 

 that indigestion may be due quite as much to the improper per- 

 formance of mouth and intestinal digestion as to that which 

 takes place in the stomach, and unless this is recognized many 

 cases will be unsuccessfully treated. 



When food is taken into the mouth it has, presumably, been 

 as fully prepared as possible by the removal of those portions 

 which are of no nutritive value. No one eats the husks of corn, 

 the shells of nuts, the gristle of meat, or similar substances, be- 

 cause experience has shown that they are of little or no nutritive 

 value, and that their digestion is practically impossible. Such 

 extraneous matters, therefore, are removed, and the food is further 

 prepared, provided this preparation is necessary, by the process 

 of cooking. In the form, then, in which the food is taken in it 

 is as fully prepared as it can be outside the body. Whatever 

 remains to be done in order that the food may be prepared for 

 absorption must be effected after it enters the alimentary canal. 



Some of the ingredients of human food are already in a con- 

 dition to be absorbed by the blood-vessels of the alimentary canal, 

 and therefore they need to undergo no change. Such ingredients 

 are water, salts, and dextrose ; and were they the only constituents 

 of the food, no digestive organs would.be needed ; but, as already 

 said, this is not the fact. The greater part of the food must be 

 changed before it can be absorbed. The first step in this conver- 

 sion is that which takes place in the mouth. 



MOUTH DIGESTION. 



When food enters the mouth it consists of a mixture of vari- 

 ous food-stuffs. In order that the changes which these food-stuffs 

 undergo may be traced thoroughly, let it be supposed that repre- 

 sentatives of all classes of food-stuffs are present, namely, (1) 

 inorganic, salts and water ; (2) carbohydrates, starch and sugar ; 

 (3) fats, or oils ; and (4) proteids. 



All the food of a fluid nature, no matter what classes of food- 



