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THE CIRCULATION OF THE BLOOD 



slowing. The action of the nerve is more properly termed augmentor. 

 The sympathetic or augmentor differs from the vagus in several particulars. 

 First, the stimulus required to produce any effect must be more powerful 

 than is the case with vagus stimulation. Second, a longer time elapses 

 before the effect is manifest. Third, the augmentation is followed by 

 exhaustion, the beats becoming after a time feeble and less frequent. 



FIG. 183. Diagrammatic Representation of the Origin and Course of the Cardiac 

 Nerves in the Dog, showing the Constituent Neurones. D 1-5, First to fifth dorsal spinal 

 nerves. Inhibitory fibers in blue, accelerators in red. (Modified from Moret.) 



The fibers of the sympathetic system, which influence the heart-beat in 

 the frog, leave the spinal cord by the anterior root of the third spinal 

 nerve. They pass by the ramus communicans to the third sympathetic 

 ganglion, thence to the second ganglion, the annulus or ansa (around the 

 subclavian artery), through the first ganglion, and along the main trunk 

 to the exit of the vagus from the cranium. There the two nerves join 



