CHAPTER V. 



CONTROL OF CIRCULATION. THE BLOOD AND 

 THE LYMPH. 



The Effect of the Emotions on Circulation. In our 

 every-day experience we have evidence of the control of 

 the heart and blood tubes by the nervous system. We know 

 that certain emotions affect the circulation of the blood ; 

 for instance, blushing and pallor. Certain emotions may 

 also quicken or retard the action of the heart. Excessive 

 grief or joy has produced sudden death by stopping the 

 beat of the heart. 



Let us look a little more closely at that part of the 

 nervous system that has such intimate relation to the 

 blood system. 



The Rhythmic Action of the Heart. In the first 

 place, the action of the heart is automatic. The heart of 

 the frog continues to beat a long time after it is removed 

 from the body. This is regarded by many as due to the 

 action of certain ganglia imbedded in the walls of the 

 heart, especially in the auricles ; while others say that 

 since the ventricle, in which no ganglia have been found, 

 may beat independently of the auricles, rhythmic contrac- 

 tion is characteristic of heart muscle, and that we are, at 

 present, unable to explain it. 



But while the impulses that originate the action of the 

 heart arise within the heart itself, still the beat of the heart 

 is constantly modified by nerve impulses reaching it from 

 without. 



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