180 JELLY-FISH, STAR-FISH, AND SEA-UllCHINS. 



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 rhj^thm 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 maximiimii 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 degaiiglionated 

 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 curi-ent 

 lemained unchancfed, 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 



