INNER VATION OF HEART AND BLOOD-VESSELS 56 L 



systole and diastole. The diminution in force often 

 appears before the diminution in frequency. 



Effect of Vagus Stimulation on the Auriculo-Veu- 

 tricular Contraction Interval. Counterpoise two 

 inverted muscle levers. Place their writing points 

 exactly above the writing point of the. electro- 

 magnetic signal. Pass fine bent pins through 

 the auricle and ventricle, respectively, and con- 

 nect them by silk threads with the muscle levers 

 ("Suspension method"). Let the drum revolve 

 at its fastest speed. When good auricular and 

 ventricular contractions are obtained, stimulate the 

 vagus trunk with a current not quite sufficient to 

 cause arrest. 



Note that the inhibition affects both the auricle 

 and the ventricle. Weak stimuli affect primarily 

 the auricles. The auriculo-ventricular contrac- 

 tion interval is lengthened. 



Irritability of the Inhibited Heart. Arrest the 

 heart by stimulating the vagus trunk. When 

 complete inhibition is secured, touch the ventricle 

 smartly with the point of the seeker. 



The ventricle will respond by a single contrac- 

 tion. 



When the inhibition is profound, the irritabil- 

 ity may be so far reduced that the heart will not 

 contract on direct stimulation. 



In addition to the effects already enumerated, 



36 



