^ 

 or THE 

 TERSITT 



CHAPTER I. 



INTRODUCTORY REMARKS ON THE ALIMENTARY 

 JUICES GENERALLY. 



SALIVA AND ITS ACTION UPON FOOD. 



INTRODUCTORY OBSERVATIONS. 



DIGESTION is the process whereby the constituents of the food are 

 rendered soluble and converted into bodies which are capable of 

 absorption. These constituents are in part mineral, and of these 

 the chief undergo no important chemical change prior to absorption. 

 The larger part consists, however, of complex carbon compounds, 

 which are for the most part insoluble in water when ingested, and 

 which, after suitable mechanical processes of division and tritu ration, 

 are subjected to the action of certain digestive juices which dissolve 

 them and render them diffusible. 



The diges- The juices above referred to are produced in, or 



tive juices the by the agency of, the epithelium cells lining the 

 products of interior of the glands which are either situated in the 

 glands 216 walls of the alimentary canal or which empty their 



secretion into it. Although these cells derive the ma- 

 terials necessary for their metabolic activity from the blood, the 

 substances which they elaborate, and which are characteristic of 

 the secretion which they help to form, are not found in the 

 blood, but are the products of the activity of the protoplasm of the 

 cells themselves. 



Enzymes or The characteristic constituents of the several juices 



ferments of which are specially concerned in the chemical changes 

 the alimentary o f the alimentary canal are certain so-called ' unor- 

 ganised' ferments, which we shall, following the sug- 

 gestion of Kiihne, denominate Enzymes. These are capable, like 

 other ferments, of initiating, under suitable circumstances, specific 

 changes in certain bodies with which they are brought into contact, 

 changes which may be incommensurably great when contrasted with 



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