OP THE ELECTRICAL ORGAN OF TORPEDO MARMORATA. 
513 
It is possible that the weaker induction current excites only the nerves upon the 
surface of the trunk ; as the strength of the stimulus increases, more nerve fibres are 
traversed by currents of sufficient intensky to excite them. That this is not, however, 
all may be inferred from the existence of similar phenomena in the case of small 
newly-born Torpedoes, when the nerve bundles are small. Thus the minimal response 
of the organ to the excitation of the second nerve by the induction shock caused by 
the break of 4 Groves in the primary circuit occurred when the secondary coil stood 
at 24 centims., and the effect amounted to -j- 220 scale (Galv. without shunt) ; 
whereas the fullest response was only obtained when the secondary coil stood at 
10 centims., and amounted to + GO scale, G. y^. 
As in the case of muscle, so here we find that the magnitude of the response affects 
the period of delay. Thus in a small Torpedo the nerve was excited 10 millims. 
from the organ. The rheotome was used as in the temperature experiment, the 
galvanometer “ window” {i.e., interval between Ko and K 3 ) being moved along so as 
to catch the commencement of the response. 
Galvanometer closure. 
•016"--018" 
■018"-'02" 
•02"--022" 
■022"- 025" 
Position of secondary coil, 20 centims. (150) 
„ „ 17-5 „ (320) . . 
12-5 „ (2000) . . 
„ „ 10 „ (4500) . . 
5 „ (9500) . . 
+ 5 
+ 5 
0 
0 
+ 15 
+ 200 
0 
+ 110 
+ 00 
+ 10 
The period of delay is here increased by •004" when the response is minimal. 
(3.) Influence of vigour and size of animal .—The influence of the state of the fish 
is an obvious one: the organ responds more quickly, the more active and vigorous the 
fish used. It is needless to illustrate this, but a more interesting rider to the above 
is the influence of the size of the fish. In contrasting the results obtained from 
different fish, all in an equally good state, but of different size, it was found that the 
period of delay was always shorter, the larger the fish. Thus in four selected fish, all 
of which were kept at 12° C. for some days, all active and vigorous, giving sensible 
shocks to the hand, and in all of which the organ, as is shown below, responded very 
fully to nerve excitation, the following results were obtained. 
a. Nerve-organ preparation from large Torpedo, 42 cm. X 29 cm. Total response 
to nerve excitation with Galv. yyo = + 650. The response commenced '007" to 
‘008" after excitation of the nerve. The nerve was excited 20 millims. from or^an, 
and, deducting ‘003" for transmission time, the period of delay is , 004". 
b. Nerve-organ preparation of medium-sized Torpedo, 26 cm. X 17 cm. Total 
response with Galv. yyy = 400. The response commenced •OOS" to ’009" after 
excitation of nerve. The nerve was excited 13 millims. from organ, and, deducting 
‘002" for transmission time, the period of delay is ’006". 
MDOCCLXXXVJI.—B. 3 IT 
