180 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
stimulation, remain constant, it is manifest that the 
responses may thus become periodic. 
In order to test the truth of this hypothesis, 
I made the following experiments. Having first 
noted the rate of the rhythm under faradaic stimu- 
lation of minimal intensity, without shifting the 
electrodes or altering the intensity of the current, I 
discarded the faradaic stimulation, and substituted 
for it single induction shocks thrown in with a key. 
I found, as I had hoped, that the maximum num- 
ber of these single shocks which I could thus throw 
in in a given time so as to procure a response to 
every shock, corresponded with the number of con- 
tractions which the tissue had previously given 
during a similar interval of time when under the 
influence of the faradaic current of similar intensity. 
To make this quite clear, I shall describe the whole 
course of one such experiment. The deganglionated 
tissue under the influence of minimal faradaic stimu- 
lation manifested a perfectly regular rhythm of 
thirty contractions per minute, or one contraction 
in every two seconds. While the position of the 
platinum electrodes and the intensity of the current 
remained unchanged, single induction shocks were 
now administered with a key at any intervals which 
might be desired. It was found that if these single 
induction stimuli were administered at regular 
intervals of two seconds or more, the tissue re- 
sponded to every stimulus; while if the stimuli 
were thrown in more rapidly than this, the tissue 
did not respond to every stimulus, but only to those 
that were separated from one another by an interval 
