514 CIRCULATION OF BLOOD AND LYMPH. 



especially in the terrapin, the inhibitory fibers are found exclusively 

 or mainly in the right vagus, and several observers have asserted 

 that in the mammals also the right vagus, as tested by direct 

 stimulation, shows a stronger inhibitory action than the left vagus. 

 Analysis of the Action of the Inhibitory Fibers. The prom- 

 inent effect of the action of the inhibitory fibers is the slowing 



Fig. 213. To show the inhibition of the heart from stimulation of the vagus. Record 

 B is the blood-pressure tracing. The vagus was stimulated twice. The marks x, x, indi- 

 cate the beginning and end of the stimulus. The first stimulation was weak; it will be 

 noted that the heart escaped and began beating before the stimulus was withdrawn. The 

 second stimulus was stronger; the inhibition lasted some time after removal of the stimulus. 

 The upper curve (K) is a plethysmographic (oncometer) tracing of the volume of the kid- 

 ney. It will be noted that when the heart stops and blood-pressure falls the kidney, like 

 the other organs, diminishes in volume. (Dawson.) 



of the rate of the heart beat. Numerous observers have called 

 attention to the fact that the vagus fibers may also cause a weaken- 

 ing in the force of the beat as well as a slowing in the rate, or, 

 indeed, the two effects may be obtained separately. This fact has 

 been shown especially for the auricles.* In the heart of the terrapin 

 * See Bayliss and Starling, "Journal of Physiology," 13, 410, 1892. 



