OF THE ELECTRICAL ORGAN OF TORPEDO MARMORATA. 
491 
in the passage of the nervous impulse down the nerve to the organ ; the nerve con¬ 
ducting more slowly than Marey had supposed—according to Jolyet, at a rate of 
7 metres in a second. 
Du Bois-Reymond. —The extensive work of du Bois-Reymond ( 18 ) remains to be 
referred to. This deals not so much with the response of the organ to excitation of 
its electrical nerve as with the peculiar behaviour of the organ itself in respect to the 
passage through it of electrical currents. The main facts which are thus brought out 
may be broadly stated as of two kinds. First, those relating to the electromotive pro¬ 
perties of the organ after the passage through it of an electrical current; and, secondly, 
those relating to the influence exerted by the organ upon the traversing current 
itself—in other words, phenomena of polarisation or after-effect, and of conduction. 
In both these respects the behaviour of the tissue varied with the direction of the 
electrical experimental current. It was thus necessary to definitely label the experi¬ 
mental current with regard to its direction through the organ, and with this view a 
current passing through the tissue from the ventral to the dorsal surface was termed 
“ homodromous,” since its direction was similar to that of the response, and a current 
passing in the opposite direction w 7 as termed “ heterodromous.” A strong galvanic 
current of short duration, whether “ homodromous,” or “ heterodromous,” is followed 
by an electromotive change which shows itself galvanometrically as a current 
passing through the organ in the direction of the shock. With weaker galvanic 
currents or currents of long duration after-effects are produced which are opposed 
in direction to the experimental current. 
The influence of the organ upon the experimental current itself is very surprising, 
for it would appear that the organ is a better conductor for “ homodromous ” than it 
is for “ heterodromous ” currents. This remarkable fact is not, according to du Bois- 
Reymond, due to the development of an excitatory change which adds to the amount 
of one current whilst it diminishes that of the one oppositely directed ; it can therefore 
only be called, for want of intelligible physical explanation, a case of “ irreciprocal 
conduction.” 
He states further that both facts are of great teleological importance, since they show 
that the shock of the organ, instead of being weakened by polarisation in the tissue, 
will be strengthened by the production of an after-effect in the same direction as 
itself, and that the organ is of such a character as to distinctly disfavour any short- 
circuiting of the current present in one column by its neighbour. To quote his own 
words, “ the organ is not insulated, but the irreciprocal conduction which we have 
recognised performs, as has been already stated, a function similar to complete 
insulation. Each column conducts its own homodromous current comparatively 
well, but bars the passage to the heterodromous current threads of all the other 
columns ; and, as this is the same for all the columns, the heterodromous current threads 
are forced to take the circuitous route round the edges of the organ, just as if the 
organ consisted of a non-conducting substance” (19). 
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