THE STORY OF THE HEART 75 



the Isle of Man which illustrates the Home Rule 

 principle in that it possesses its own House of Keys, 

 regulating its local affairs. These ganglia are respon- 

 sible for keeping the heart duly at work. The muscle 

 of the heart requires to be stimulated to action like 

 every other muscle of the body, and so we discover 

 that the sympathetic system, represented by these 

 detached parts in the heart substance, will duly super- 

 vise and control the ordinary actions whereby the 

 the blood is circulated. Connected with the heart we 

 find a branch of the sympathetic system passing 

 into the heart and connecting itself with the cardiac 

 ganglia just mentioned. Also from the brain sys- 

 tem a branch of a very large and important nerve 

 known as the vagus is also connected with certain of 

 the ganglia of the heart. The meaning of that ap- 

 parent dual control over the heart's action becomes 

 clear when, as the result of experiment, it is shown 

 that whilst the sympathetic nerves stimulate the 

 action of the heart and quicken it, the vagus nerve 

 acts in the opposite direction and tends to slow the 

 heart's movements. We thus discover that provision 

 is made for the perfect control of the heart in health. 

 If circumstances arise when it is necessary for the 

 heart's work to be increased, the sympathetic nerve 

 will effect this end. If, on the other hand, the heart 

 requires to be slowed down, the vagus nerve will then 

 come into play. 



THE RELIEF OF THE HEART. So far a very com- 

 plete nervous control is exercised over the central 

 organ of the circulation. There yet remains, however, 

 a fourth nerve which demands attention. This nerve, 

 it was discovered, instead of conveying orders from 

 the central nervous system, carries messages in the 

 reverse direction. In other words, its purpose is to 



