EXPERIMENTS IN STIMULATlOX. 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 lithoc3^sts 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 couie 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, w^hen the period 

 of latency will be reduced to its rninimum, 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 arousinof the tissue into 



