THE ACTION OF THE VAGUS 



123 



In the piece before stimulation this is 9 mm., during stimulation it is 

 11 mm., and after stimulation it soon returns to its initial height. A 

 third change to be observed is with regard to an altered rate of trans- 

 mission of the contraction from the auricle to the ventricle. Before 

 stimulation the auricular beat was practically completed before the 

 ventricular began. Under the influence of the stimulation the time 



Fig. 100. — Effects of Tetanising the Vagus with Different Strengths of 

 Stimuli. In Tracing 1 the Secondary Coil was at 19 cms. ; in 2 at 18 cms. ; 

 in 3 at 16 cms. ; in 4 at 15 cms. ; and in 5 at 14 cms. from the Primary 

 Coil. Time Tracing Seconds. 



relation gradually changed and showed that the wave of contraction 

 passed more readily from auricle to ventricular, i.e. that conduction 

 between the two was favoured. 



In tracing 3, with slightly increased strength of stimulus, slowing 

 is more pronounced, from 35 to 25 per minute. The height of each is 



