GO THE HUMAN BODY. 



CHAPTER V. 

 THE CIRCULATION. 



SECTION I. 1, The blood is found in every part of the 

 body. But the body does not hold it as a sponge holds 

 water. It is rather like a house which has a supply of 

 water carried through it in pipes. The blood in the body 

 is all contained in pipes, called blood-vessels. 



2, It is constantly in motion. Starting from the heart, 

 it moves through the blood-vessels off to distant parts of 

 the body, and then back to the heart again, making a 

 circle. The heart and blood-vessels are, therefore, called 

 the organs of circulation. 



3, The blood-vessels are called arteries, capillaries, and 

 veins. Coming out of the heart is a very large artery, 

 called the aorta. This gives off branches as it passes on, 

 and these branches, again, other branches, growing smaller 

 as they divide, until at length the smallest branches are 

 called capillaries. 



4, The capillaries are very numerous, very small, and 

 very close together. They form a net-work in every inch 

 of bone and muscle and skin and brain, a net-work 

 finer than the finest silk. We can not put a fine needle- 

 point into the skin without opening some of these capil- 



SUGOESTIONS TO TEACHERS. SECTION I. A beefs or sheep's heart, from 

 the butcher's, will show all the parts named in the text. The action of the 

 heart-muscle and of its valves may be partly illustrated with a Davidson's 

 syringe. 



