104 
MANUAL OT NATURE STUDY. 
entrance of veins and departure of arteries, dis¬ 
tinguishing between those of the pulmonary sys¬ 
tem and those of the systemic. The heart may 
be represented as a pump, forever receiving blood 
from the lungs and body, and continually pumping 
it again to various parts of the system. (See third 
year work.) 
Color of blood ? When a finger is cut, what is 
the great natural process that stops the flow of the 
blood ? (Clotting.) What is the use of blood to 
the system ? How does it create heat ? How does 
it promote growth and repair waste ? 
“Blood, then, is a very wonderful fluid.’ * * * 
But you will not wonder at it when you come 
to see that the blood is the great circulating market 
of the body, in which all the things that are wan¬ 
ted by all parts, by the muscles, by the brain, by 
the skin, by the lungs, liver and kidneys, are 
bought and sold. What the muscle wants it buys 
from the blood; and so with every other organ and 
part, as long as life lasts, this buying and selling 
is forever going on, and this is why the blood is 
forever on the move, sweeping restlessly from 
place to place, bringing to each part the things it 
wants, and carrying away those with which it has 
done. When the blood ceases to move, the market 
is blocked, the buying and selling cease, and all 
