1012 
DR. W. H. GASKELL ON THE RHYTHM OF THE HEART OF 
Trom these experiments the conclusion can be drawn that the impairment of the 
nutrition of the heart caused by the removal of the circulation is not of itself sufficient 
to take away from the vagus the power of reducing the force of the contractions to the 
null point; but rather that, in addition, some unknown factor, upon which this diminu¬ 
tion of the beats depends, is more powerful at one time than at another. 
In all that has been said hitherto, no evidence has been given that the vagus is able 
to cause any slowing of the rate at which impulses are discharged from the motor 
ganglia, but, on the contrary, clear evidence that it is able to accelerate that rate, and 
although the large majority of my curves point directly to that conclusion, yet occa¬ 
sionally a curve is obtained in which an undoubted slowing has taken place. In some 
cases it is possible that the slowing may be due to the failure of certain imp uls es to 
produce a contraction as is undoubtedly the case in the slower ventricular beats seen 
in Plate 69, fig. 15, where the stimulation of the vagus caused the ventricle to beat for 
a time synchronously with every second auricular beat. On the other hand, such 
slowing as is seen in Plate 67, fig. 13, where the recovery of the rate of rhythm after 
the end of the stimulation was gradual both in auricles and ventricle, cannot be 
explained, except upon the supposition that the nerve stimulation had slowed the rate 
of the discharges from the motor ganglia. 
Indeed, the fact that the vagus is able to cause a slowing of the heart's rhythm is so 
well established as not to admit of doubt; all I contend for is, that that slowing is not 
always a sufficient explanation of the phenomenon known as vagus inhibition. 
Further, I venture to suggest that the hypothesis that the Aagus contains two sets 
of fibres going to the motor ganglia, of which the one causes upon stimulation accelera¬ 
tion, the other a slowing of the rate of discharge from the motor ganglia, is no more 
necessary than the similar supposition that the nerve contains two sets of fibres sup¬ 
plying the muscular tissue, of which the one causes a diminution, the other an increase 
of the force of the contractions. 
The experiment from which Plate 67, fig. 13, is taken shows clearly the rapid diminution of the power 
of the vagus to produce a slowing of the heart when the heart is removed from the body, and suggests 
that that removal affects the action of the nerve upon the rate of rhythm in the same direction as it 
affects its action upon the force of the muscular contractions. Thus, in Plate 67, fig. 18, the effect of the 
first stimulation of the nerve immediately after the heart was suspended, is given. The second stimulation, 
about a minute after the first, still caused a decided slowing, but very much less marked in extent than 
before. The third stimulation showed that the nerve was no longer able to produce any slowing, although 
the effect upon the force of the contractions was as great as in the previous stimulations. 
On the influence of the vagus nerve upon the excitability of the ventricular muscle . 
Seeing that the vagus acts so powerfully upon the force of the muscular contrac¬ 
tions, it is natural to expect that it also has an influence upon the excitability of the 
muscular tissue. The nature of this influence can be determined by the following 
considerations. 
