68 PRACTICAL PHYSIOLOGY 



stimulate the sympathetic. Use fine electrodes and a strength of 

 current just comfortable to the tongue. 1 



The heart-beats are accelerated and augmented after a long latent 

 period. This effect is prolonged for a considerable time after the 

 excitation has ceased. The after effect is decreased frequency and 

 amplitude. 



Next pass the electrodes under the vago-sympathetic trunk. The 

 heart-beats will* either be arrested (inhibited) after a brief latent period 

 or decreased in frequency and amplitude. There is a short after 

 effect; the heart soon escapes, even if the excitation be continued. 

 The after effect is usually increased frequency and amplitude. The 

 returning beats frequently show the staircase effect. Sometimes the 

 sympathetic effect overpowers the influence of the vagus. To stimulate 



FIG. 69. Excitation of vago-sympathetic. Note the after effect a staircase 

 augmentation of the . heart-beat. The stars indicate the beginning and end of 

 stimulation. The downstroke represents contraction. (See footnote, p. 60.) The 

 time is marked in seconds. (L.H.) 



the pure vagus fibres, the cerebrum is destroyed, the cervical cord 

 divided, and the spinal bulb excited. During the state of complete 

 inhibition the heart may not respond to mechanical excitation. 



There is little evidence in support of the old view that the excitatory 

 state is transmitted through the heart and the contraction regulated in 

 sequence by the nerve ganglia of the heart. The ganglion cells, which 

 wander into the embryonic heart some days after it has started beating, 

 can be removed without disturbing the cardiac rhythm. Extra-cardiac 



J The electrodes may be made of fine covered wires. The ends, for ^ inch, are 

 stuck together by melted paraffin. The paraffin is grooved with a knife, so as to 

 lay bare the wires at a point inch from their end. The wires are passed 

 through slits in a small piece of cork. The cork may then be pinned in any 

 suitable position. 



