NUTRITION. 107 



burned to enable it to work; and the food or fuel must be 

 brought .therefore, to every corner of our frames. 



Digestion. A great part of our food is solid, and could 

 not of itself get outside of the alimentary canal. To render 

 it available it must be dissolved so that it can soak through 

 the walls of the stomach and intestines. For this purpose 

 we find a set of digestive organs which make solvent juices 

 and pour them on the food which we swallow, and so get 

 it into a liquid state in which it can be absorbed. 



Circulation. The solution containing our digested food 

 if it simply soaked through the walls of the alimentary 

 canal, would be of no use to distant parts, as the brain, or 

 the muscles of the limbs. We find, therefore, in the body 

 a set of tubes containing blood, and called blood-vessels: 

 the blood is driven through these by a pump, the heart. 

 Much of the dissolved food passes into the blood-vessels of 

 the alimentary canal, and from them is carried by other 

 blood-vessels to every organ, no matter how remote. As 

 the blood flows unceasingly, round and round in its vessels, 

 from part to part, the organs concerned in moving and 

 conveying it are called circulatory organs, and the blood- 

 flow itself is known as the circulation. 



Absorbents. Some of the dissolved food is taken up 

 into another set of tubes in the walls of the alimentary 

 canal; these tubes carry it afterwards into the blood-vessels. 

 They are called the absorbents. 



Why must many foods be dissolved? What is accomplished by 

 the digestive organs? 



What are the blood-vessels? What enters those of the alimentary 

 canal? How are organs distant from the alimentary canal nourished? 

 Why are the organs which keep up the blood-flow called circulatory 

 organs? What is meant by the circulation? 



What are the absorbents? Where do they convey the foods 

 which they take up in the walls of the alimentary canal? 



