NERVI ACCELERANTES 63 



from the deep face of the gangUon ; these latter must be cut. The ganghon 

 with the accelerantes branches are thus fully freed. 



To apply electrodes to the latter, lift the ganglion well clear of all tissues 

 by means of one of the ligatures in the left hand and apply the electrodes to 

 the origins of the accelerantes from the ganglion, taking care that the part of 

 the accelerantes stimulated and the electrode points themselves are clear for a 

 distance of several mm. from all contact with the tissues. 



Cover the dissection with a cotton-wool swab wrung out in warm Ringer- 

 Locke fluid. 



y. Return to the right carotid ; establish its connexion by means of 

 cannula with the kymograph tubing (previous exerc. V). Obtain graphic 

 pressure-trace. 



VI. Observation of the accelerantes effect (text-fig. 28). Uncover thoracic 

 wound. Set going the induction coil's primary circuit. Apply electrodes to the 

 accelerantes, as described above. When you are ready your colleague opens 

 the bridge-key of the secondary circuit. Mark abscissa for moment of 

 commencement of stimulation on the arterial pressure- trace. Measure the long 

 latency of the accelerator effect, also the long after-action. Compare duration 

 of latency and of after-effect with those of your vagus inhibition curve 

 (previous exercise). Repeat with various strengths of stimulating current. 

 The length of the after-action is greater with stronger than with weaker 

 currents. 



It sometimes happens that the faradization of the nerve produces inhibition 

 of the heart by escape of the stimulating current to cardiac branches of the 

 vagus ; the accelerantes in their farther course to the heart soon join the cardiac 

 branches of the vagus. This escape is likely to occur if the accelerantes are not 

 well cleared by dissection. When this escape occurs the result as shown by 

 the kymograph record is (1) vagus inhibition, followed, on withdrawal of the 

 stimulus, by (2) the acclerantes effect. This is in accord with observations that 

 prove that when vagus and accelerantes are separately but concurrently 

 faradized the vagus effect predominates during the stimulation but does not 

 prevent the accelerantes effect taking place afterward. A way of avoiding in 

 the present experiment the escape of the stimulation to the vagus, if that 

 occurs, is to stimulate mechanically. This can be done by placing a thickish 

 thread round the body of the ganglion and drawing it tight, crushing the 

 ganglion. A pure accelerantes effect is thus obtained, and with a second 

 ligature farther distal can be repeated. Another way of avoiding vagus 

 complication is to inject atropine (cf. exerc. V, obs. 19). 



