CHAPTER XIV. 



ALIMENTATION. 



Section I. Preliminary remarks on secreting glands and mucous 

 membranes. 



Section II. Food-principles ; proteids, fats, carbo-hydrates, water, saline 

 and mineral substances : chemical composition of the body : average compo- 

 sition of milk, bread, and meat. Concluding remarks. 



Section I. In our last chapter, we described the methods by- 

 means of which the blood is supplied with one of its most vital 

 constituents, oxygen. In the next three chapters, we shall con- 

 sider how the blood is supplied with those materials through 

 the alimentary canal, which it also constantly requires to main- 

 tain the life and growth of the body. 



The subject of alimentation, or the process by which the 

 body is nourished, naturally falls into three divisions, viz. : — 



(1) Food. 



(2) Digestion. 



(3) Absorption. 



In order, however, to make the subject more intelligible, it 

 will be necessary to make a few preliminary remarks upon the 

 construction of secreting glands and mucous membranes. 



Secreting glands. — The secreting glands differ from other 

 glands, such as the lymphatic glands, the tonsils, Peyer's 

 patches, etc., by being always devoted to the function of 

 secretion, and by discharging the secretions they form through 

 little tubes or ducts which open exteriorly. The lymphatic 

 glands and bodies of allied structure are often spoken of as 

 ductless glands, in order to distinguish them from these true 

 secreting glands provided with ducts. 



A secretion is a substance elaborated from the blood by cell 



164 



