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MR, G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
four observers experimented was the heart-apex of the Frog. This, in being a mus¬ 
cular tissue deprived of its centres of spontaneity, constitutes a very fair physiological 
parallel to the paralyzed bell of a Medusa. In the paper alluded to, the authors 
confine themselves to describing the effects of the constant current in producing 
rhythmic response on the part of the heart-apex ; but in a note previously published 
by Dr. Foster in the same journal (vol. iii., p. 400), it is shown that minimal faradaic 
stimulation also has the effect of throwing the heart-apex into rhythmic action. The 
artificial rhythm is not, indeed, so perfect as that which I obtained in the case of 
Aurelia; but it is nevertheless of an unmistakable character. With regard to it 
Dr. Foster makes the following suggestive remark:—“We may infer that the cardiac 
muscular tissue differs for some reason from ordinary muscular tissue in a disposition 
towards rhythmic rather than continuous contraction; and that the influence of the 
ganglia is probably not rhythmic but continuous, whatever the exact nature of that 
influence may be.” And, as already observed, Dr. Foster and Mr. Dew Smith have 
also obtained rhythmic response to constant stimulation in the case of the Snail’s 
heart. 
The only other observation bearing on this subject with which I have met, is one 
that was published by Dr. Burden Sanderson and Mr. Page in the ‘ Proceedings of 
the Poyal Society.’ The tissue on which these observers experimented was the 
excitable leaf of Dionoea, and they were able to show that slightly less than minimal 
stimulation produces rhythmic response in these tissues. The response in this case 
was estimated, not by the occurrence of a contraction—the stimulation employed being 
too feeble to cause any contraction—but by the occurrence of the electrical disturbance 
which, as these authors have shown, always constitutes the first result of stimulation, 
and therefore takes place even in cases where the stimulus is not strong enough to 
cause contraction. The following are the words in which the fact is stated by its 
observers :—“ When a leaf is excited at regular intervals by single shocks of such 
intensity as to be just beyond the limit of adequacy, so that the slightest diminution 
would render them futile, it is sometimes observed that the effects become rhythmical. 
Thus, in a series of 54 successive excitations, we obtained the following results:— 
Excitations 1, 2, 3, and 4, were effectual; but of the 16 excitations following every 
other was futile, the alternate ones only being followed by excursions (i.e., of the 
electrometer) ; then followed during eight minutes a series of futile excitations, after 
which the leaf was allowed to rest for two minutes. On resuminof, the alternate 
rhythm again appeared for six excitations, then becoming modified, so that an 
excursion followed every fourth instead of every third excitation, a state of things 
which continued for a quarter of an hour.” 
Thus, then, as a final result, we see that, not onty in the case of the lowest 
organisms, and not only in the case of the paralyzed tissues of the Medusae, and of the 
Frog’s tongue, but also in that of the Frog’s heart, the Snail’s heart, and of the 
excitable tissues of the Dionoea, there is observable a tendency to a more or less 
