THE STORY OP DIGESTION 35 



though the circumstance may appear, the stomach 

 has really very little to do with the digestion of food 

 at all, that is, when compared with the bulk of the 

 digestive work at large. The action of the stomach 

 is no doubt highly important, but it does not by any 

 means include those actions through which the 

 larger amount of the diet is converted into a form 

 ready to be assimilated by and into the blood. The 

 first digestive work accomplished in the mouth is 

 division of the food by the teeth. This is an 

 extremely important action, but one unfortunately 

 too much neglected by the vast majority of people. 

 The proper division of the food by the teeth is 

 essential for the healthy performance of digestion, 

 first, because the stomach cannot digest masses of 

 food ; and second, because unless food be thoroughly 

 divided by the teeth it cannot be thoroughly mixed 

 with the saliva which is in itself an essential for the 

 perfect digestion of starchy foods. Returning pres- 

 ently to consider the teeth themselves, we may 

 illustrate the axiom that digestion begins in the 

 mouth, by considering the duties performed by the 

 saliva or " water " of the mouth. This fluid is fur- 

 nished by three sets of glands. Of these glands, 

 one set exists in front of the ears, these being known 

 as the parotid glands. The other two pairs, called 

 sub-maxillary and sub-lingual glands, are situated in 

 the floor of the mouth. Each pours its secretion 

 into the mouth through a special tube or duct, the 

 saliva representing a " secretion " as it is termed, 

 manufactured by cells. The essential units in the 

 salivary glands are living cells, which, from the 

 blood supplied to the glands, elaborate or manufac- 

 ture the particular secretion afforded by these 

 organs. Each cell in this way may therefore be 



