688 
ME. G. J. EOMANES ON THE LOCOMOTOE SYSTEM OF MEDUSAE. 
staircase effect is lost in that of tetanus), progressive shortening of the intervals between 
successive stimuli has the effect of progressively diminishing the number of steps in a 
staircase, and this by increasing the difference between the heights of the successive steps. 
Again, if a staircase has been built up by shocks thrown in at seconds’ intervals, and the 
rate of stimulation be now suddenly changed to six seconds’ intervals, the maximum level 
of the tracing that was obtained by the more rapidly succeeding shocks may be observed 
slightly to sink. This greater tolerance of the medusoid than of the cardiac tissue 
towards rapidity in the succession of stimuli is doubtless connected with the same 
differences in their constitution that leads to what I have called the shorter memory of 
the one than of the other. In this connexion it may also be stated that a staircase 
has more steps in it if caused by a weak than if caused by a strong current (compare 
tigs. 1 & 4), and that if the strength of the current be suddenly increased after the 
Fig. 4. 
maximum level of a staircase has been attained by a feeble current, this level admits of 
being slightly raised (see fig. 4). 
Lastly, the cases of the heart and of Aurelia appear not quite to coincide in one 
other particular ; for I find that in Aurelia the staircase action is so pronounced, that 
a stimulus which at the bottom of a staircase is of less than minimal intensity, is able, 
at the top of a staircase, to give rise to a contraction of very nearly maximum intensity. 
That is to say, by employing an induction stimulus of slightly less than minimal inten- 
sity in relation to the original irritability of the tissue, no response is given to the first 
two or three shocks of a series ; but at the third or fourth shock a slight response is 
given, and from that point onward the staircase is built up as usual. This was the 
case in the experiment of which fig. 1 is a record, no response having been given to the 
first two shocks. Now, as Dr. Bowditch does not state that a staircase may thus be 
built up by means of stimuli which at the beginning of the process are of less than 
minimal intensity, I infer that in the case of the heart this peculiarity is not observable. 
With regard to this interesting staircase action, two questions naturally present 
themselves. In the first place, we are anxious to kiiow whether the arousing effect 
which is so conspicuous in a staircase series is due to the occurrence of the previous 
stimulations , or to that of the previous contractions', and, in the next place, we 
should like to know whether, during the natural rhythm of the tissue, each con- 
