1016 DR. W. H. GASKELL ON THE RHYTHM OF THE HEART OF 
heating experiment. Plate 69, fig. 18, shows the corresponding effect when standstill 
is produced by clamping. 
A consideration of these and similar curves shows that when, whether from the 
effect of clamping alone or from the combined effects of heating the motor ganglia 
and clamping, the ventricle is not beating, stimulation of the vagus causes a series of 
ventricular beats which commences as a rule some little time after the end of the 
stimulation. These contractions last for a certain time, and then the ventricle again 
becomes quiescent, until, with a new stimulation of the nerve, a new group of con¬ 
tractions is produced. Again, the contractions in each of these series are synchronous 
with the auricular contractions, and are strong vigorous contractions such as would 
have been produced had the ventricle been beating when the nerve was stimulated. 
This shows that the beats in each of these series, as far as their mere occurrence 
is concerned, are due to motor impulses which pass to the ventricle at the same 
rate as to the auricles, and therefore that during the previous quiescence the motor 
impulses were still passing to the ventricle, but were not able to produce any con¬ 
tractions. Again, these series of contractions do not as a rule take place during 
the stimulation of the nerve, but some time after the stimulation, and the position 
of each series corresponds closely to the position of the maximum contractions seen 
after the end of the stimulation of the nerve in the ordinary curve of vagus stimu¬ 
lation! An explanation, therefore, of this action of the vagus is clearly given by 
the supposition that by the action of the nerve the excitability of the ventricular 
muscle is increased at the same time that the force of the contractions is increased. 
Hence as soon as the excitability is sufficiently raised the motor impulses which have 
been rendered inefficient by the action of the clamp, or by the action of heat upon the 
motor ganglia, are able to cause contractions : and these contractions last until by 
the passing off of the vagus influence the excitability has again sunk too low for 
the impulses to be able to cause a contraction. 
The beats in each series are not necessarily synchronous with every impulse from the beginning to the 
end of the series. As far as I have seen they are usually synchronous in the middle beats of each group, 
but the series may begin and end with one or two beats which are synchronous with every second auricular 
contraction instead of with every one. This latter form of curve simply denotes that the rise and fall of 
the excitability has not been so abrupt as in the first case, as can easily be seen by drawing a diagram to 
represent the curve of excitability in relation to the strength of the impulses. 
Further, it was noticed in the course of the experiment from which Plate 69, fig. 17,-is taken, that 
after a while the same strength of stimulation caused a series of ventricular contractions when the 
auricles and sinus were not heated, and no effect whatever when the nerve was stimulated during 
the time of heating; in other words, when the strength of the impulses was made still weaker by the 
heating, the rise of excitability caused by the vagus stimulation Was not sufficient to make those impulses 
efficient to cause ventricular contractions. 
Also (as is seen in Plate 69, fig. 17, B, C, D) during the course of the experiment each series of 
ventricular contractions lasted on the whole a shorter and shorter time, and commenced later and later 
after the end of the stimulation—a fact which is to be explained by the progressive exhaustion of the 
whole heart. 
