164 
MR, G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSiE. 
(c.) As the fact of this wonderfully rhythmic response to faradaic irritation was 
quite unexpected by me, and as it seemed to be a fact of great significance, I was led 
to investigate it in as many of its bearings as time permitted. First, I tried the effect 
on the rhythm of progressively intensifying the strength of the faradaic current. I 
found that with each increment of the current the rate of the rhythm was increased; 
and this up to the point at which the rhythm began to pass into tetanus due to sum¬ 
mation of the successive contractions. But between the slowest rhythm obtainable by 
minimal stimulation and the most rapid rhythm obtainable before the appearance of 
tetanus, there were numerous degrees of rate to be observed. I here append another 
tracing to show the effect on the rate of the rhythm of alterations in the strength of 
the current (fig. 2). 
Fig. 2. 
It will also be observed from this tracing that, in consequence of the current having 
been strengthened slightly beyond the limit within which strictly rhythmic response 
was attainable, the curves in the middle part of the tracing, where the current was 
strengthened, are slightly irregular. This irregularity is of course due to the first 
appearance of tumultuous tetanus. If the faradaic stimulation had in this case been 
progressively made still stronger, the irregularity would have become still more pro¬ 
nounced up to a certain point, when it would gradually have begun to pass into 
more persistent tetanus. But as in this case, instead of strengthening the current 
still further, I again weakened it to its original intensity, the rhythm immediately 
returned to its original rate and regularity. 
(d.) The next point I investigated was the persistency of any given rate of rhythm 
under faradaic stimulation of constant intensity. I found this persistency to vary 
with the vigour of the specimens experimented on, as well as with other conditions 
which I need not wait to specify ; but in all cases the persistency was much greater 
than I had expected. For the sake of brevity I shall confine myself in this connexion 
to giving the particulars of one experiment. A detached quadrant of Aurelia, whose 
normal rate of rhythm was 18 per minute, had its lithocysts removed, and then formed 
the subject of the experiment. The faradaic stimulation supplied to it was of slightly 
more than minimal intensity, and the resulting rhythm was perfectly regular at the 
rate of 38 per minute. This absolutely perfect rhythm continued, without once 
faltering or changing its rate, for an hour and a quarter (tracing, fig. 1). At the end 
of this time single omissions in the series of contractions began to occur at long 
intervals— i,e after every one or two hundred rhythmic contractions, a short pause 
