THE CARDIAC AUGMENTOR CENTER. 761 



heart. Accordingly, irritation of the medulla, of the lower extremity 

 of the divided cervical cord, of the inferior cervical ganglion (stellate 

 ganglion), or of the superior dorsal node, is attended with acceleration of 

 the heart-beat and increase of its strength (in the dog and the rabbit) ; 

 or, if the heart's action has already ceased, with renewal of its beat, 

 without change in blood-pressure. 



It is probable that the accelerator nerves and those increasing the strength of 

 the heart are distinct, both with respect to their anatomical arrangement, and 

 with regard to their susceptibility to various poisons. 



When the medulla oblongata or the cervical cord is irritated, the vasomotor 

 nerves situated in them are also irritated. In consequence, the vessels that 

 derive their motor fibers from the irritated area contract, and the blood-pressure 

 is markedly increased. As, however, the increase in blood-pressure alone causes 

 acceleration of the heart-beat, the irritation described does not directly demon- 

 strate the existence of accelerator fibers in these central structures. The ex- 

 periment would be convincing only if before the irritation is applied the blood- 

 pressure were enormously lowered by destruction of the splanchnic nerves, so that 

 the former could no longer exert an accelerating influence. Indirectly it can be 

 demonstrated also that, if all of the nerves of the cardiac plexus, therefore also 

 the accelerator fibers, are extirpated, after irritation of the medulla or the cervical 

 cord the pulse-frequency does not rise (in consequence of increase in blood-pressure) 

 in the same degree as before the extirpation. 



The center is in any event not in a state of tonic irritation, for section 

 of the nerve does not cause slowing of the heart. Destruction of the 

 medulla or of the cervical cord itself likewise has a negative effect. 

 Nevertheless, in this instance also, the splanchnic nerve must be pre- 

 viously destroyed, to bring about marked lowering of the blood-pressure, 

 in order that the reduction in the number of heart -beats that occurs in 

 consequence of the lowered blood-pressure after destruction of the 

 cord shall not be incorrectly interpreted as being due to destruction of the 

 accelerator center. 



Cardiac accelerator fibers pass, according to the statements of earlier 

 investigators and of v. Bezold, in part into the cervical sympathetic, 

 in part through the vagus to the heart, and irritation accelerates the 

 heart -beat or strengthens the cardiac contractions, or both. The inhib- 

 itory fibers of the vagus lose their irritability more readily than the accel- 

 erator fibers, but they are more irritable than the latter. 



The fibers of the vagus that influence the force of the contractions are situated 

 in the frog in the nerves of the septum. The acceleration of pulse attending 

 increased muscular activity is attributable to irritation of the accelerator fibers, 

 occurring in conjunction with stimulation of the motor nerves, while the irritation 

 of the inhibitory nerves is diminished. The acceleration appears especially in de- 

 bilitated convalescents. The heart, after a period of increased activity, later 

 resumes its normal action. Practice in the form of activity favors such resumption. 



The cases described by Tarchanoff and van de Velde are most striking. In 

 these, human beings were able, solely through the influence of the will (at rest 

 and without alteration of respiration) , to increase the number of pulse-beats even 

 to twice the normal. 



Direct irritation of the accelerator nerve gives rise to slowly developing effects, 

 which disappear gradually after cessation of the irritation. If the vagus and the 

 accelerator are irritated simultaneously, only the inhibitory action of the vagus 

 makes its appearance. According to Hunt, in the case of this simultaneous 

 irritation, the action of that nerve appears which is most strongly irritated. If 

 during the activity of the accelerator nerve, the vagus is suddenly irritated, 

 prompt reduction in the number of heart-beats occurs, and if the irritation of 

 the vagus ceases the acceleration soon begins again. The activity of the accel- 

 erator nerves (in the frog) is enfeebled by cold and increased by heat. 



