156 A MANUAL OF PHYSIOLOGY 



logue of the nervous channels by which impulses may reach the 

 cardiac centres in the medulla, we may add that there must be 

 an extensive connection between them and the cerebral cortex, 

 since every passing emotion leaves its trace upon the curve of 

 cardiac action. The so-called ' reflex cardiac death,' which is 

 an occasional consequence of intense psychical influences (anxiety, 

 fright, etc.), may be due to the prolonged excitation of the 

 cardio-inhibitory centre, as well as to the disturbance of other 

 centres in the bulb by the cortical storm. It is a remarkable 

 fact, too, and one that can only be explained by such a con- 

 nection, that although in the vast majority of individuals the 

 will has no influence whatever on the rate or force of the heart, 

 except, perhaps, indirectly through the respiration, some persons 

 have the power, by a voluntary effort, of markedly accelerating 

 the pulse. In one case of this kind it was noticed that per- 

 spiration broke out on the hands and other parts of the body 

 when the heart was voluntarily accelerated. A rise of blood- 

 pressure due to constriction of the vessels has also been observed. 

 The effort cannot be kept up for more than a short time, and 

 the pulse-rate quickly goes back to normal. It has been recently 

 shown that this peculiar power is more common than has been 

 supposed, and that where it is present in rudiment, it can be 

 cultivated, although it is a dangerous acquisition. 



As an example of the direct action of a chemical stimulus 

 on a cardiac centre, we may cite the inhibition produced by 

 injection of adrenalin into a vein (p. 201), and as an instance of 

 the direct action of a physical change, the slowing of the heart 

 in asphyxia as the blood-pressure rises (p. 172). The variation 

 in the pulse-rate associated with changes in the position of the 

 body, to which we have already referred (p. 98), is brought about 

 by direct stimulation of the inhibitory centre by the increase 

 of blood-pressure in the medulla oblongata when a person who 

 has been standing assumes the supine, or even the sitting, posture. 

 But it is also due in part to changes in the amount of muscular 

 contraction, since muscular exercise causes acceleration of the 

 heart either reflexly, through afferent muscular nerves, or by a 

 direct effect of waste products of the metabolism of the muscles 

 on the cardiac centres in the bulb or on the heart itself (p. 229). 



Theoretically, quickening of the heart might be caused either 

 by a diminution in the inhibitory tone or by an increase in the 

 activity of the augmentor centre ; and slowing of the heart 

 might be due either to a diminution in the augmentor tone, if 

 such exists, or to an increase in the activity of the inhibitory 

 centre. So that it is not always easy to interpret such results 

 as we have quoted above. But it would appear that under 

 ordinary conditions the rate of the heart is mainly regulated 



