MR, G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSHL 
165 
would occur of a length equal to the time occupied by a single contraction. These 
omissions then gradually became more and more frequent, till finally they gave rise to 
well-marked irregularity (tracing, fig. 3). Shortly afterwards all movements entirely 
Fig. 3. 
ceased, and failed to be aroused even by strengthening the current. This cessation of 
response through exhaustion took place rather more than an hour and a half after the 
first commencement of stimulation. I then allowed the tissue to remain quiescent for 
fifteen minutes, and again stimulated, but no response was given. After the lapse of 
a further fifteen minutes response was given to the faradising current at the moment 
of its closure, but not during its passage. I now gave the tissue another quarter of an 
hour’s rest, and then obtained responses to faradisation of a partly rhythmic nature. 
Lastly, on waiting for another quarter of an hour— i.e., one hour from the time at 
which the persistent stimulation for an hour and a half had ceased—the movements 
in response to faradisation w r ere strictly rhythmic, although for the same strength of 
current the rate of their rhythm was now slower than before—viz. : 28 per minute. 
(But on placing another pair of electrodes on another part of the tissue, the original 
rate of 38 per minute could be obtained.) I now again persistently tetanised for an 
hour, and throughout that time obtained perfectly regular and sustained rhythm of 28 
per minute. Exhaustion had not again supervened when the observation terminated. 
(e.) Such being the facts, the question arises as to their interpretation. At first I 
was naturally inclined to suppose that the artificial rhythm was clue to a periodic 
variation in the strength of the stimulus, caused by some slight breach of contact 
between the terminals and the tissue on each contraction of the latter. This supposi¬ 
tion, of course, would divest the phenomena in question of all physiological meaning, 
and I therefore took pains in the first instance to exclude it. This I did in two ways : 
first, by observing that in many cases (and especially in Cyancea capillcita) the rate of 
the rhythm is so slow that the contractions do not follow one another till a considerable 
interval of total relaxation has intervened; and second, by placing the terminals 
close together so as to include only a small piece of tissue between them, and then 
firmly pinning the tissue all round the electrodes to a piece of wood placed beneath 
the Medusa. In this way the small portion of tissue which served as the seat of 
stimulation was itself prevented from moving, and therefore the rhythmic motions 
