CIRCULATION" OF THE BLOOD. 63 



11. The thin walls of the capillaries allow the liquid part of the 

 blood to soak out and nourish the tissues, and to soak back into the 

 capillaries bearing waste matter. 



12. The veins are thin walled, and collapse when empty, while the 

 arteries are thick walled, and stand open when empty of blood. 



13. Arteries carry blood from the heart, while veins carry it toward 

 the heart. 



14. The veins have valves which allow the blood to pass toward 

 the heart, but not away from it. 



15. Any intermittent pressure on the veins aids the blood flow. 



1 6. The blood flow is most rapid in the arteries, slower in the veins, 

 slowest in the capillaries. 



17. Gravity influences circulation. 



Questions. i. Why do the large arteries lie deep? 



2. In which direction should the limbs be stroked to promote circu- 

 lation? 



3. How does slapping the hands around the body warm the ringers? 



4. How can a horse or a cow be comfortable with the head down 

 for a long time? 



5. Why are the walls of the left ventricle thicker than those of the 

 right ? 



