1014 
DR W. H. GASKELL ON THE RHYTHM OE THE HEART OE 
tion, at other times some considerable time after the end of tbe stimulation. Thus in 
Plate 68, fig. 14, the ventricle was beating synchronously with every third beat of 
the auricles ; for a definite period after the end of the stimulation of the vagus its 
rhythm was changed so that it beat synchronously with every second instead of with 
every third auricular beat. Similar figures might be given to show how the vagus 
causes the ventricle to beat synchronously with every beat of the auricles instead of 
with every second beat. 
These curves show that stimulation of the vagus increased the excitability of the ven¬ 
tricle sufficiently to enable it either wholly or partially to recover for a time the normal 
sequence of its beats upon those of the auricles, and also that increase of excitability 
took place at the same time as the maximum increase in the force of the contractions. 
In the second place, stimulation of the vagus may cause a primary slowing of such a 
character that a variable number of auricular beats are dropped out from the ventricular 
curve, and then afterwards the ventricle may regain its original rhythm or even become 
synchronous with every beat of the auricles (Plate 69, fig 15). 
Further, this slowing of the ventricle may not only be coincident with an acceleration 
of the auricles, but in fact is more likely to occur when stimulation of the nerve causes 
a marked auricular acceleration. This, at first sight paradoxical, assertion follows neces¬ 
sarily upon the arguments put forward in the first part of this paper, if it be assumed 
that the vagus diminishes the excitability of the muscle at tbe same time that it 
depresses the strength of the contractions; for the greater rapidity of the auricular 
contractions denotes not only quicker but also weaker impulses from the motor ganglia; 
and it is clear that, if the impulses be weakened at the same time that the excitability 
iis lessened, a larger number of impulses will require to be summed up in order to 
produce a contraction, than if the excitability only is diminished. 
Again, if the clamp be placed across the middle of the ventricle, and the contractions 
of the base and apex of the ventricle be registered, the same diminution of excitability 
can be observed. Thus, when the apex is beating synchronously with every second or, 
as in Plate 69, fig. 16, with every fourth beat of the base, then coincident with the 
diminution and acceleration of the contractions of the base, which occur during the 
stimulation of the nerve, the beats of the apex take place at a slower rate than before, 
because each apex contraction corresponds to a larger number, and therefore probably 
to a longer series of base-contractions than before the stimulation. 
Thus in the instance given (Plate 69, fig. 16) I have marked the corresponding contractions on the two 
sides with the same numbers, and it is seen that before the stimulation of the vagus the relation between 
the rhythm of the apex and the base was such that each apex-contraction corresponded to four base- 
contractions. During the stimulation the beats of the base became weaker and more frequent, while 
those of the apex were so much slower that only two beats took place, of which the first corresponded to 
twelve beats of the base and the second to eight beats. Af ter the stimulation the original relation between 
the rhythm of the apex and base was restored, so that each apex-contraction again corresponded to four 
base-contractions. Curves similar to this are those most frequently obtained with the clamp in this 
position. 
