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DR. W. H. GASKELL ON THE RHYTHM OE THE HEART OE 
7. There is a limit to the extent to which a series of inefficient impulses can raise 
the excitability of the muscle so that the ventricle can remain absolutely quiescent, 
even although the impulses still pass to it, when those impulses are sufficiently 
weakened, as will be shown in the second part of this paper. 
The assertion that the rhythm of the heart is normally due to separate impulses 
discharged from the motor ganglia in the venous sinus, each of which causes a contrac¬ 
tion of the cardiac muscle, is not intended to imply that these impulses necessarily 
travel along simple nerve fibres without passing through one or more interpolated 
ganglion cells, but only that whatever the nature of the path of the conduction of the 
nervous impulse may be, separate discharges from the motor ganglia at one end of the 
path reach the muscle as separate impulses at the other end. 
So, too, I have spoken of the motor ganglia in the venous sinus without meaning 
thereby to assert that these ganglia may not extend slightly beyond the sinus into the 
auricular septum as asserted by Lowit* (for as a matter of fact experiments which I 
have made expressly for this purpose have convinced me of the truth of his assertion), 
or that the other groups of ganglion cells found in different parts of the heart may 
not upon occasion perform motor functions. 
The whole question of the action of these different groups of nerve cells deserves 
separate discussion. In this paper I have purposely abstained from that discussion 
because my object is to describe certain definite well established facts rather than to 
enlarge upon all the various topics connected with the theory of the heart's action. 
In this first part of the paper, therefore, I have confined myself to the question of 
the relation of the muscular tissue to the impulses coming to it, and have attempted to 
prove not only that the normal beat of the heart is dependent upon separate impulses 
coming to the cardiac muscle, but that, in addition, the muscular tissue is of such a 
character that if from any cause the impulses discharged from the motor ganglia 
should become too weak to cause a contraction, the rhythmical action of the heart can 
still continue though at a slower rate, because each of these impulses, abortive though 
it is to produce a contraction, increases the excitability of the muscle, and therefore 
the latter responds rhythmically to every two or three of the impulses coming to it. 
This relation between the stimulus and the excitability of the muscle, which in the 
whole heart is to be regarded as a special safeguard for the maintenance of its 
rhythmical action and not the prime cause of that action, is on the other hand the 
chief factor in the causation of the rhythm of the isolated apex of the ventricle. 
The large number of investigations on this subject which have been made of recent 
years may, as far as the rhythm is concerned, be summed up by saying that the 
muscular tissue of the apex contracts rhythmically under the influence of a sufficient 
continually acting stimulus, whether that stimulus be electrical, chemical or mechanical. 
Thus spontaneous rhythmical contractions occur when the constant current or a weak 
tetanizing current is sent through the tissue, and the rapidity of the rhythm varies 
# Pfluger’s Archiv, Bd. xxiii., S. 313. 
