NATURAL HISTORY. 



27 



" Blest son of foresight, lord of fate I 

 That awful independent of to-morrow ! 

 Whose work is done ; who triumphs in the past ; 

 Whose yesterdays look backward with a smile." YOUNG. 



taming the denser fluids, and reflects the rays of light in a 

 different manner. 



71. Howis the blood in the human body circulated and purified ? 



First, the heart sends the blood to all the capillaries through one 

 set of blood-vessels called arteries. Then the blood is brought back 

 to the heart by another set of blood-vessels called veins. Next by 

 the blood which returns by the veins is impure, and is sent by 

 another set of arteries from the heart into the lungs, to be purified 

 by the air we breathe. Then it is brought back to the heart by 

 another set of veins. Thus there are two sets of arteries and veins 

 through which the blood is all made to pass ; first, through the 

 body and back to the heart for the purpose of nourishment, and 

 then through the lungs and back for the purpose of purification. 



72. The right side of the heart receives and sends out the impure blood. The upper 



division receives it from the body 

 through two large veins. Then the 

 blood passes to the lower division of 

 the heart, where it is sent to the 

 lungs through one 

 with two branches, 



large artery 

 one for each 

 lung. This is the pulmonary artery . 

 The left side of the heart receives 

 and sends out the pure blood. The 

 upper portion receives it from the 

 lunss through three large veins. 

 Then the blood passes to the lower 

 division of the heart when it is sent 

 to the capillariet all over the body 

 through one large artery called the 

 aorta. 



73. Why is the blood regarded as so important an agent in 

 animal economy ? 



Because the blood is the vehicle of life to every atom of our 

 organization. By properties peculiar to itself, all the various fluids 

 of our body are produced from it, and every particle of bone, 

 muscle, membrane, nerve, and vessel must have existed as an in- 

 gredient of the blood, and have been conveyed to its appropriate 



