1022 
DR. W. H. GASKELL OK THE RHYTHM OE THE HEART OF 
which is situated on the opposite side of the clamp. That this will help to explain many of the cases of 
diminished relaxation after yagus stimulation there can he no doubt. Still, I have seen cases in which 
such an explanation does not seem sufficient, especially when the ventricle is beating with alternately 
strong and weak beats. 
Further, such an explanation will not account for the peculiar shape of the diastolic line in the series 
of ventricular beats which occur as a consequence of vagus stimulation when the ventricle has been 
reduced to standstill either by tightening the clamp or heating the auricles and sinus. The series of 
curves given in Plate 69, figs. 17 and 18, show, firstly, that when the ventricle is made to beat with the 
same rhythm as the auricles the relaxation between the beats is very much less than that of the quiescent 
ventricle ; and, secondly, that the muscle relaxes less between consecutive beats near the commencement of 
each group of beats than later on in that group, although as is seen in curve C, fig. 17, the rate of rhythm 
has remained the same throughout the series of beats. This diminution of relaxation at the commence¬ 
ment of each group is clearly not due to any mechanical action of the auricular contractions ; for, as is 
seen in all the figures, and especially in fig. 18, where the maximum contractions of the auricles occurred 
before the ventricle began to beat, those contractions caused no appreciable effect upon the position of 
the ventricular lever. 
I am inclined, therefore, to think that it is possible that the increase of the contraction force caused by 
the action of the vagus nerve may be accompanied by an increase of tonicity, and that the diminution in 
the contraction force is certainly accompanied by a diminution of tonicity. I am the more emboldened to 
consider this a possibility by the fact that Aubert* has already, from observations on the action of the 
Dog’s heart, suggested that cardio-tonic nerves for the heart exist, and by their action cause the greater 
relaxation which exists during the stimulation of the vagus and the diminution of relaxation which he 
noticed after the end of the stimulation of the nerve. 
The effect of atropin , muscarin, and curare upon the action of the vagus. 
Before mentioning the effect of these poisons upon the vagus action, I will endeavour 
to sum up briefly their actions upon the motor ganglia and the muscular tissue 
respectively, as far, at least, as can be judged from these present experiments. 
Atropin applied to the ventricle alone does not alter its rate of rhythm or the force 
of its contraction except after repeated applications. From this we can say that 
atropin does not prevent the muscle from contracting to its full extent or diminish its 
excitability except in extreme doses. 
Muscarin applied to the ventricle alone rapidily diminishes the force of its contrac¬ 
tions without altering the rate of rhythm, and may ultimately make the ventricle beat 
synchronously with every second auricular beat. Muscarin, therefore, prevents the 
full contraction of the muscle and diminishes its excitability. 
Curare applied to the ventricle alone produces at first no alteration in the force of 
its contractions or in its rhythm ; after repeated doses it diminishes the contraction 
force and often causes the ventricle to respond once only to every two auricle contrac¬ 
tions. Curare, therefore, ultimately prevents the full contraction of the muscle and 
lowers its excitability. 
Atropin applied to the sinus and auricles only, slows the rhythm both of auricles 
and ventricle. With this slowing it causes the ventricle to beat synchronously with 
* Pluger’s Arcbiv, Bd. v., S. 621. 
