NERVOUS CONTROL 73 



Influence of the Blood-Supply upon the Cardiac Centre 



Rise in the arterial pressure within the skull causes reflex 

 slowing of the heart by stimulating the vagus centre. 

 Increase in the hydrogen ion content of the blood has the 

 same effect. 



From what has been said, it is clear that, owing to its 

 being controlled by the central nervous system, the heart 

 possesses a much greater latitude of adaptation than if it 

 were independent. The function of the cardiac centre 

 is to regulate the output of the heart according to the needs 

 of the body as a whole. It must be remembered however 

 that we are here dealing with only one aspect of a complex 

 story. The greatest increase in the activity of the heart 

 occurs as the result of an unusual demand for oxygen by 

 the tissues, and this demand is met not only by a quickening 

 of the circulation but by changes in other systems. Until 

 these have been separately considered, we shall not be in 

 a position to understand fully the significance to the 

 animal economy of the factors affecting the activity of 

 the heart. 



