2 PHYSIOLOGY OF ALIMENTATION. 



in pari of animal, in part of vegetable origin. Among the 

 vegetable fats are the cottonseed and olive oils, while familiar 

 examples of animal fats are found in butter, cream, and 

 the fats of fat meat. Water makes up the bulk of the 

 inorganic material which we consume. Among the other 

 inorganic constituents of our food are the all-important 

 salts, which come to us in part as natural components of 

 our diet, in part as condiments, or as constituents of the 

 so-called mineral waters. 



Representatives of all these classes are found in the or- 

 dinary mixed diet, and no diet is sufficient for man for any 

 length of time unless it contains representatives of all these 

 classes. This mixed diet enters the alimentary tract, some- 

 times finely divided, sometimes in a state of coarse division. 

 Some of the constituents of the food may be in suspension 

 or in solution in water. At times the food is cooked, at 

 other times uncooked, and in this state is started on its 

 way through the alimentary tract. The alimentary tract 

 takes up or absorbs from this heterogeneous mass which 

 enters the mouth certain constituents of the food either 

 in the condition in which they are consumed by the indi- 

 vidual or after they have been aetejg^pon by the secre- 

 , tions of the alimentary tract. UBelfides altering the physical 

 and chemical constitution of the food the alimentary 

 tract therefore acts as an absorptive system. Interestingly 

 enough, however, it also acts as an excretory system. All 

 these various functions, not only the elaboration of the 

 food by physical and chemical means, but also those of 

 absorption and excretion, are included under the general 

 caption, alimentation. 



We shall now take up these functions separately, direct- 

 ing our attention first to the mechanical phenomena which 

 are associated with the journey of the food through the 

 alimentary tract. 



2. Mastication. The articulation of the inferior maxillary 

 bone with the skull allows of a variety of movements al! 



