340 ELEMENTS OF GENEKAL SCIENCE 



meal which leaves a residue of cellulose, such as oatmeal, 

 bread, fruit, and vegetables ; and to go to the toilet regularly. 

 If water is taken at mealtime it should not be used to wash 

 down unchewed food. 



Since mental states have such an effect on the flow of 

 the digestive juices and on the movement of food along the 

 alimentary canal, everyone should try to see that mealtimes 

 are as pleasant as possible. If one is very tired, it is often 

 better not to eat until after one has rested. 



347. Transportation of food to the cells. The food, after 

 its complex preparation in the alimentary canal, passes with 

 water through the intestinal wall into the small capillaries 

 of the circulatory system and is carried to all the cells of 

 the body. The circulatory system consists of a series of 

 branching tubes through wlu'ch the blood is iorced by the 

 heart. The blood flows away from the heart through arteries, 

 which divide and redivide into smaller and smaller branches. 

 They terminate in many extremely small tubes, known as 

 capillaries, which are interwoven so as to constitute a fine 

 network. These capillaries are directly in contact with the 

 cells of the body. The capillaries unite and form the veins 

 which finally, as large veins, lead back to the heart. So rapid 

 is the movement of blood that it is accurately estimated that a 

 given particle may sometimes leave the heart, make its round 

 to one of the more distant parts of the body, and return to 

 the heart within half a minute. 



348. The heart and circulation. The branching of the 

 circulatory system is much too complex to show in any 

 single picture, but the accompanying diagram shows the kind 

 of branching. It is to be remembered that every cell in the 

 body is reached directly or indirectly by a capillary. The 

 diagram also shows the relation between the circulation 

 through the lungs and through the rest of the body. The 

 right side of the heart pumps the blood through the lungs. 

 The blood is returned to the left side of the heart, which 



