THE HUMAN BODY. 



ing in moderation. Excitement of any kind increases the 

 number and force of heart-beats so that they can be felt, 

 and sometimes heard. In the affection called palpitation, 

 the action of the heart is unnaturally rapid, and some- 

 times hard enough to shake the body. 



7, The heart has been called a pump. It is really 

 a double pump. There are two streams flowing out of 

 it with each contraction, and two streams flowing into it 

 with each relaxation. The two sides 

 of the heart have no direct communi- 

 cation, and are often spoken of as the 

 right and left heart, as if they were 

 separate. 



8. There are, accordingly, two dis- 

 tinct circles of blood. One begins at 

 the right ventricle, goes through the 

 pulmonary artery to the lungs, and 

 back through the pulmonary veins to 

 the left auricle. This is called the 

 pulmonary circulation, or the lesser 

 circulation. 



Fi 32 The other begins at the left ventricle, 



REPRESENTATION OF THE and goes through the aorta, to be clis- 

 GREATER AND LESSER tributed to all parts of the body, and, 



CIRCULATION. \ 



passing through the capillaries and 

 veins, is poured into the right auricle by the vena cava 

 superior and the vena cava inferior. This is called the 

 systemic or greater circulation. 



9, Let us observe a contraction and its effect. Suppose 

 the auricles to be full. The blood has been pouring 

 into the right one from the venae cavoe, and into the left 

 from the pulmonary veins. Now the auricles contract. 



