EXPERIMENTS IN STIMULATION. 59 
identity of natural and artificial staircase action 
may be placed beyond all doubt by an experiment 
in which the effects of induction shocks and of 
ganglionic discharges are combined. ‘To accomplish 
this, all the lithocysts save one are removed, and 
a staircase is then built up in the ordinary way by 
successive induction shocks. It will now occasion- 
ally happen that the ganglion originates a discharge 
during the process of constructing the staircase, 
which is being built up by the artificial stimuli ; 
when this happens the resulting contraction takes 
its proper rank in the series, and this at whatever 
point the natural contraction happens to come in. 
Thus, then, to summarize and conclude these 
observations, we have seen that if a single stimula- 
tion, whether of a natural or artificial kind, is 
supplied to the excitable tissues of a jelly-fish, a 
short period, called the period of latency, will 
elapse, and then the jelly-fish will give a single 
weak contraction. If, as soon as the tissue has 
relaxed, the stimulation is again repeated, the 
period of latency will be somewhat shorter, and 
will be followed by a somewhat stronger contrac- 
tion. Similarly, if the stimulation is repeated a 
third time, the period of latency will be still 
shorter, and the ensuing contraction still stronger. 
And so on up to nine or ten times, when the period 
of latency will be reduced to its minimum, while 
the force of the contraction will be raised to its 
maximum ; so that in the jelly-fish, the effect of a 
series of excitations supplied at short intervals from 
one another is that of both arousing the tissue into 
