REACTION-TIME OF GONIONEMUS MURBACHII. 85 



an instrument readable to hundredths or thousandths of a second. 

 For this purpose a Hipp chronoscope, readable to thousandths, 

 was placed in circuit with the stimulus electrodes and the reac- 

 tion-key. The electrodes were connected in such a way that the 

 chronoscope circuit was made, and the record thereby started, the 

 instant the stimulus circuit was completed. The motor reaction 

 of the medusa in response to the electric shock served to break 

 the chronoscope circuit, thus stopping the record. The experi- 

 menter was then able to read from the chronoscope dials the 

 time which intervened between stimulus and reaction (reaction- 

 time). Cattell's falling screen served as a regulator for the 

 chronoscope. 1 



The reaction-key used in these measurements of the time of 

 reaction to electric stimuli consisted of a frame for the support 

 of an easily sliding rod, one end of which carried a cork disk and 

 the other a platinum point by which the circuit was completed. 

 The movement of the medusa against the disk when a stimulus was 

 given, caused the rod to slip upward, thus breaking the chrono- 

 scope circuit. 



REACTION-TIME TO ELECTRIC STIMULI. 



Gonionemus reacts to an electric current, indirectly applied, in 

 from one to five seconds, according to the strength of the stimu- 

 lus, and the position of the electrodes. The following averages 

 indicate the facts. Since it was not possible to get more than 

 four or five satisfactory reactions in series with any one animal, 

 the averages, unless otherwise marked, are for five reactions. 



I. Reactions to a 4-Mesco-cell current, with electrodes on 

 opposite sides of the bell, not in contact with the organism. 

 M. 1.023 sec. ; M.V. 0.168 sec. ; R.V. 2 16.0. 



II. Same, with 2-cell current. M. 1.489 sec.; M. V. 0.199 

 sec. ; R. V. 13.4. 



III. Reactions to a 4-cell current, with electrodes 5 mm. apart 

 in contact with the margin of the bell. M. 0.605 sec. ; M. V. 

 0.128 sec. ; R. V. 21. 



Repetition of the 4-cell stimulus at intervals of a minute causes 



1 For fuller description of the chronoscopic method used see Harvard Psycholog- 

 ical Studies, Vol. I., pp. 601-605. 



2 R.V. = (M.V. X I0 ) / M - = Relative Variability. 



