1885.] of the Heart in Fishes, especially that of the EeL 123 



Effects of Vagal Stimulation on the Properties of the Muscular Tissue 

 of the different Parts of the Heart. 



In the investigation of these effects the cardiac action was regis- 

 tered by means of a simple arrangement of the graphic method. 

 Simultaneous tracings of the auricular and ventricular action were 

 obtained by means of two writing levers suspended in the horizontal 

 position by slender elastic bands ; these levers were brought into con- 

 nexion with the auricle and ventricle respectively by threads. In 

 order to prevent locomotion of the heart it was sometimes necessary 

 to afford a fixed point by holding in a clamp the bands passing into 

 the dorsal aspect of the auricle. 



At times a simultaneous record of the contractions of the auricle 

 and ventricle was obtained by a single writing lever : (1) by attaching 

 the threads from the auricle and ventricle to the same lever, or 

 (2) by connecting the lever by the auricle alone (by means of a 

 thread), and then firmly fixing the apex of the ventricle. The 

 auricular and ventricular beats are then recorded on a single 

 tracing. 



I shall take each part of the heart in succession, and briefly con- 

 sider the effects observed in each. 



(1.) Effects of Vagus Stimulation on the Ventricular Muscle. 



A large number of experiments have clearly shown that the 

 ventricle is not directly affected by stimulation of the vagus nerve. 



As has been already mentioned, the automatic rhythmic power of the 

 ventricle is low, and the ordinary rate of action of this part in the 

 intact heart results not from the spontaneous rhythm of the ventricle 

 itself, but in consequence of the rapid action of the sinus and auricle, 

 from which parts the contraction is propagated to the ventricle. The 

 ventricular contraction is started off by the other parts of the heart ; 

 its inherent rhythmic power remains latent. It is obvious then that 

 an arrest of the action of the other parts of the heart would at once 

 lead to a suspension of the ventricular activity. The ventricle, 

 deprived of the impulses which ordinarily start off its contraction, 

 must necessarily stand still until such time as the starting off impulses 

 come again into play, or until its latent automatic rhythm begins to 

 manifest itself — an event which, in ordinary circumstances, would not 

 occur for a very considerable length of time. So that with regard to the 

 suspension of the ventricular rhythm caused by vagus stimulation, the 

 removal of the normally efficient cause of that rhythm is the reason of 

 the ventricular standstill, i.e., the ventricle stands still because the 

 other parts of the heart have stopped action. 



The excitability of the ventricular muscle during inhibition of the 



