1881.] 



On the Rhythm of the Heart of the Frog. 



199 



II. " On the Rhythm of the Heart of the Frog, and on the 

 Nature of the Action of the Vagus Nerve." By W. H. 

 Gaskell, M.D. Cantab. Communicated by Dr. Michael 

 Foster, Sec. R.S. Received December 8, 1881. 



(Abstract.) 



The method of investigation employed by the author is as follows : — 

 The heart with the vagus nerve intact having been removed from the 

 body together with a portion of the oesophagus, a thread is tied to the 

 very apex of the ventricle and another to the loose flap which is dis- 

 closed at the junction of the two auricles when the two aortic trunks 

 are cut away. The piece of the oesophagus removed with the heart 

 is held firmly in a suitable holder and the heart suspended between two 

 horizontal levers by means of the two threads which are attached to the 

 auricles and ventricle. Between the two levers a clamp is placed, the 

 edges of which can be approximated to any degree by means of a fine 

 micrometer screw ; the two limbs of this clamp are placed one on each 

 side of the suspended heart, and by means of the micrometer screw, the 

 tissue between the two edges can be simply held firm or compressed to 

 any extent required. In this way, with the clamp in the auriculo- ven- 

 tricular groove, the beats of both auricles and ventricle are registered 

 simultaneously and separately ; the contractions of the auricles pull 

 the upper lever downwards, those of the ventricle the lower lever 

 upwards. Similarly by varying the position of the clamp the con- 

 tractions of any two adjacent portions of the heart can be studied, as 

 for example, sinus and ^.auricles, base and apex of the ventricle, &c. ; 

 heat, cold, and poisons can be applied to the tissue on the one side of 

 the clamp and not on the other ; and under all these various condi- 

 tions the effects of stimulation of the vagus can be observed. 



The paper is divided into two parts ; Part I, on the rhythm of the 

 heart ; Part II, on the action of the vagus nerve. 



In Part I reasons are given for the view that discrete impulses 

 pass from the motor ganglia to the muscular tissue, that, therefore, 

 the normal rhythm of the heart is dependent upon rhythmical dis- 

 charges from the motor ganglia, and is not due to the production by 

 the cardiac muscle of rhythmical results from, a constant stimulation. 

 This follows from the fact that any influence which, when applied to 

 the auricles and sinus alone, causes an alteration in the rhythm of 

 the auricles, affects the rate of the ventricular beats synchronously; 

 while the same influence applied to the ventricle alone, causes no 

 alteration in the rhythm of the auricles or in the synchronism of the 

 ventricular with the auricular beats. Thus heat applied to the ven- 

 tricle alone does not alter its rhythm although it reduces the force of 



vol. xxxiii. p 



