Page:Proceedings of the Royal Society of London Vol 60.djvu/47

Rh (7) The peripheral organ rh y th m (m ultiple response) varies from about 100 per second at 5° C. to about 280 p er second a t 35° C.

(8) One causative factor in the production of the peripheral rhythm is th e susceptibility of th e excitable tissue to respond to the current set up by its own activity (self excitation).

(9) In the uninjured fish m echanical or electrical excitation of the surface of the skin beyond the lim its of the organ evokes a reflex response with a long delay (0*03" to 0*3") ; th is reflex response consists of groups of shocks, each group showing the peripheral organ rhythm, b u t 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 m ay consist of a direct peripheral organ effect followed by such a reflex effect.

(11) The m inimal total reflex delay at 20° C. is 0-023", giving a central excitatory time of about 0-01".

(12) The reflex or central rh y th m in our specimens showed a m aximum rate of 12 per second and an average ra te of from 3 to 4 per second.

(13) The num ber of separate groups in th e reflex response recurring at the intervals m entioned 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 num ber of effective plates w ith th eir nerves, and in 10 cm. of excited organ cannot possibly be less than 75 volts, and is probably m uch nearer 150 volts. As in our specimens the num ber 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 .l. of 0’07 volt for each plate.

The authors fu rth er conclude th at, 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 presumably 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 0 ‘008" to 0’01". (5.) 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.