THE FROG, AND OH THE ACTION OF THE VAGUS NERVE. 
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rate of rhythm either of ventricle or auricles is produced; the rate of the auricular 
beats continues the same ; the ventricular beat follows upon each auricular with the 
same regularity as before, and, in fact, as far as the rhythm is concerned the ventricle 
might not have been heated (Plate 67, fig. 2). That the heating was effective, however, 
the figure clearly shows, for the force of the ventricular contractions is markedly 
diminished during the time that the muscle was heated: a fact of considerable 
importance, as proving that heat acts upon the muscular tissue of the heart in such a 
way as to diminish the force of its contractions apart altogether from the rapidity of 
the rate of rhythm of those contractions. 
This experiment seems to me positive proof that in the whole heart the rhythm is 
due to discrete impulses proceeding from certain motor ganglia to the muscular tissue, 
each of which impulses causes a contraction of that tissue. Further evidence to the 
same effect is given by a series of results which may be generalized as follows 
Any influence which, 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 initial alteration in 
the rhythm either of ventricle or auricles. 
Thus cold slows both the auricular and ventricular beats when applied to the 
auricles and sinus, while the same amount of cold produces no effect on the rhythm 
when applied to the ventricle alone. Atropin sulphate (1 p.c. solution) dropped on to 
the auricles and sinus slows the rate of beating of the whole heart most markedly 
(Plate 70, fig. 26 B) while the same solution applied to the cut-open ventricle produces 
no initial effect upon the rhythm. So, too, with muscarin sulphate, a marked slowing 
when applied to the auricles and sinus ; no alteration of rhythm, for some time at all 
events, when confined to the ventricle. (See Plate 70, figs. 26 A, 27.) 
Many more instances of the same kind might be given, but enough has been said 
already to permit us to formulate the following proposition :— 
The rhythmical contractions of the heart as a whole are caused by discrete impulses 
which proceed rhythmically from certain motor ganglia to the auricles and ventricle. 
The apparent discrepancy between this assertion and the rhythmical phenomena 
exhibited by the isolated ventricle and apex will be discussed at the end of this part 
of my subject. 
On the want of seguence between the ventricular and auricular contractions. 
If, however, we conclude that separate impulses pass from the motor ganglia to the 
ventricle, the further question arises, What conditions are necessary so that each one 
of these impulses should cause a contraction of the ventricular muscle \ 
In the ventricle or apex alone we know, from the experiments of Kronecker,* that 
# Op. ait. 
