Electromotive Properties of Electrical Organ of Malapterurus. 39 



(7) The peripheral organ rhythm (multiple response) varies from 

 about 100 per second at 5 C. to about 280 per second at 35 C. 



(8) One causative factor in the production of the peripheral 

 rhythm is the susceptibility of the excitable tissue to respond to the 

 current set up by its own activity (self excitation). 



(9) In the uninjured fish mechanical or electrical excitation of the 

 surface of the skin beyond the limits of the organ evokes a reflex 

 response with a long delay (0'03" to 0'3") ; this reflex response con- 

 sists of groups of shocks, each group showing the peripheral organ 

 rhythm, but separated from its neighbour by a considerable interval 

 of time (reflex or central rhythm). 



(10) In the uninjured fish electrical excitation of the skin over 

 the organ evokes a response which may consist of a direct peripheral 

 organ effect followed by such a reflex effect. 



(11) The minimal total reflex delay at 20 C. is 0'023", giving a 

 central excitatory time of about O'Ol". 



(12) The reflex or central rhythm in our specimens showed a 

 maximum rate of 12 per second and an average rate of from 3 to 

 4 per second. 



(13) The number of separate groups in the reflex response recurring 

 at the intervals mentioned in the preceding paragraph was in our fish 

 limited to from 2 to 5. 



(14) The E.M.F. of each single change in the organ response 

 depends upon the number of effective plates with their nerves, and in 

 10 cm. of excited organ cannot possibly be less than 75 volts, 

 and is probably much nearer 150 volts. As in our specimens the 

 number of plates in series in 1 cm. of organ was 180, this gives a 

 minimal possible E.M.F. of 0'04 volt, and a probable E.M.F. of 

 0*07 volt for each plate. 



The authors further conclude that, since each lateral half of 

 the organ is innervated by the axis cylinder branches of one efferent 

 nerve cell, and has no independent excitability, the specific characters 

 of the reflex response of the organ express far more closely than 

 those of muscle the changes in central nerve activity, and are pre- 

 sumably those of the activity of a single efferent nerve cell. 



The single efferent nerve cell, the activity of which is thus for the 

 first time ascertained, shows 



(a.) A minimum period of delay of O'OOS" to O'Ol". 



(6.) A maximum rate of discharge of 12 per second. 



(c.) An average rate of discharge of 3 to 4 per second. 



(d.) A susceptibility to fatigue showing itself in the discharge 

 failing after it had recurred from two to five times at the above 

 rates. 



