86 BLUSHING. 



If the blood tubes leaving the heart could all be united, 

 they would be best represented by a funnel with its tube con- 

 nected with the heart. If another funnel were placed with 

 its mouth to the mouth of the first, their point of union, the 

 widest point, would represent the capillaries; and if the 

 second funnel had a wider tube than the first, it would fairly 

 represent the veins which return the blood to the heart. 



Nourishment of the Walls of the Heart and Blood 

 Tubes. The Cardiac (Coronary) arteries send blood into the 

 muscular walls of the heart, and these arteries, like others, 

 divide, forming capillaries, through which the heart muscle is 

 nourished. The Cardiac veins return the blood to the right 

 auricle. 



The larger arteries and veins also have small blood tubes 

 in their walls which supply them with blood. 



The statements which have been made concerning the 

 action of the heart, and the blood tubes connected with it, 

 apply equally to both halves of the heart, which work simul- 

 taneously ; the chief difference in the two sides of the heart 

 is that the right side pumps dark blood, while the left pumps 

 bright blood. 



The left ventricle is much stronger, as it has to pump the 

 blood against so much greater resistance. 



Blushing. How is it that the face sometimes flushes so 

 suddenly ? Because of some emotion, you say. But how 

 does the emotion bring this about ? 



The following experiment, that has been repeatedly made 

 on the rabbit, may help us to answer the question. If the 

 sympathetic nerve, in the neck, which sends branches to the 

 head, be cut, the ear of that side at once grows red; i.e., it 

 blushes. But if the end of the nerve connected with the ear 

 be stimulated, the ear becomes pale. We have already learned 

 about the muscles in the wall of the arteries, and their action. 



