THE CIRCULATION. 



these ganglia, irritation of the cord caused no change in the number of 

 heart-beats. 



The accelerator nerves have their origin in the medulla oblongata 

 and pass out from the spinal cord through the anterior roots of the 

 second, third and fourth dorsal spinal nerves ; then by the white rami 

 to the stellate or first thoracic ganglion, and then by the annulus of 

 Vieussens to the inferior cervical ganglia and thence to the heart, 

 either to its cardiac plexus or more probably to the cardiac muscle. In 

 the frog the vagus contains accelerator fibers. Here the accelerator 

 fibers leave the spinal cord mainly through the third spinal nerve, then 

 by the ramus communicans to the third sympathetic ganglion up the 

 cervical sympathetic to join the ganglion on the trunk of the vagus 



Fig. 85- Acceleration of the Heart following an Irritation of an 

 Efferent Branch of the First Thoracic Ganglion in a Curarized Dog. 

 Action of Accelerator Nerve. 



PC, Pressure in the carotid. E, Irritation of the nerve by an induction 

 current. S, Time in seconds. The frequency of the pulse is more than doubled. 



(GLET.) 



and proceed with it to the heart. Hence the name vago-sympathetic 

 nerve in the case of the frog. Irritation of the sympathetic in the 

 frog before it joins the vagus causes the heart to beat quicker and it 

 may not relax completely; the latent period is long and the force of 

 the heart-beat is increased. The conduction of the impulses from the 

 auricle to the ventricle is increased leading to an acceleration in the 

 succession of the beats of the auricle and ventricle. After the stimu- 

 lations end the heart slows. Because the heart-beats are augmented 

 and accelerated at one time and at another independently of each other, 

 it is supposed that there are two kinds of fibers, accelerators and aug- 

 mentors. In the acceleration of the heart by irritation of the 

 accelerators, both the diastole and systole are shortened, the volume of 

 the heart diminishes, the systoles of the auricle and ventricle become 

 more energetic. The increased rate of heart-beat persists a certain 



