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ME. G. J. EOMANES ON THE LOCOMOTOR SYSTEM OF MEDUSA. 
posteriori because, after the arrival of every artificially started wave, the time required 
for the ganglion to originate another wave was precisely the same as if it had itself 
originated the previous wave. 
(i d ) In view of these results it occurred to me, as an interesting experiment, to try the 
effect on the natural rhythm of exhausting a ganglion thus situated by throwing in a 
great number of shocks at the other end of the strip. I found that after 500 single 
shocks had been thrown in with a rapidity almost sufficient to tetanize the strip, im- 
mediately after the stimulation ceased, the natural rhythm of the ganglion, which had 
previously been 20 in the minute, fell to 14 for the first minute, 18 for the second, and 
the original rate of 20 for the third. In such experiments the diminution of rate is 
most conspicuous during the first 15 or 30 seconds of the first minute. Sometimes 
there are no contractions at all for the first 15 seconds after cessation of the stimula- 
ting process ; and in such cases the natural rhythm, when it first begins, may be as slow 
as one half or even one quarter its normal rate. All these effects admit of being pro- 
duced equally well, and with less trouble, by faradizing the strip, when it may be even 
better observed how prolonged may be the stimulation without causing any thing 
further than such slight exhaustion of the ganglion as the above results imply*. 
§ 2. Naked-eyed Medusce. — (a) It would be impossible to imagine movements, on the 
part of so simple an organism, more indicative of physiological harmony than are 
the movements of Sarsia. One may watch several hundreds of these animals while they 
are swimming about in the same bell-jar, and never perceive, as in the covered-eyed 
* In this description I have everywhere adopted the current phraseology with regard to ganglionic action — 
a phraseology which embodies the theory of ganglia supplying interrupted stimulation. But although I have 
done this for the sake of clearness, of course it will be seen that the facts harmonize equally well with the 
theory of continuous stimulation which I am engaged in working out, but the publication of which is for the 
present postponed. (See, for an outline of the new theory, the abstract of this paper in the Proc. E. S. vol. xxv.) 
Indeed the fact last mentioned in the text would agree with the new better than with the old theory of gan- 
glionic action ; for my other experiments on the deganglionated tissues of Aurelia prove how difficult these 
tissues are to exhaust. Hence if the natural rhythm in the case of the above-mentioned experiments is due 
to the contractile, as distinguished from the ganglionic, element, we should expect the period of quiescence 
between cessation of the faradaic stimulus and the renewal of spontaneity to be short ; because this interval, 
according to the new theory, is the expression of the time required for the contractile tissue to recover exhaus- 
tion sufficiently to enable the ganglionic stimulation — which had become less than minimal in relation to the 
diminished excitability of the contractile tissue — to become minimal. I may also state that, according to the 
new theory, the reason why a contractile wave is reinforced while passing a lithocyst is probably the same as 
that to which all reflex action is by that theory supposed to be due, viz. the molecular disturbance in an afferent 
nerve being of the nature of a vibration, and the continuous somewhat less than minimal stimulation supplied 
by the ganglion being also of the nature of a vibration, if the wave-rates in these two vibrations are supposed 
synchronous , when the afferent disturbance reaches the ganglion the amplitude of the ganglionic vibrations 
would be somewhat increased. Hence the stimulation, which was previously being continuously supplied by 
the ganglionic vibrations, and which before being augmented by the arrival of the afferent vibrations was 
somewhat less than minimal, would now become minimal or somewhat more than minimal. And, conversely, 
the facts of inhibition are explained by this theory of ganglionic action as due to an interference of vibrations 
the rates of which are not synchronous* 
