OF THE ELECTRICAL ORGAN OF TORPEDO MARMORATA. 
533 
into a state of prolonged excitation. Now it is only in cases of very vigorous response 
to nerve excitation that the peculiar prolongation of the response referred to in Part II. 
is seen. There is thus every reason to suppose that this prolonged change is the same, 
whether its precursor be an induction shock or the shock of the nerve-organ response 
itself The fact that in the one case the tissue is quiescent, whilst in the other it is 
in a state of functional activity, does not really affect the matter. The experiments on 
summation to be now referred to show that the tissue is capable of responding to two 
stimuli occurring within , 01" of each other, and that an after-effect may be procured 
even when the tissue is in a state of activity by leading an induction shock through 
the organ '02" after a response has been evoked by excitation of its nerve. To these 
experiments we now turn. 
Summation of effects .—Before proceeding to experiments designed to show the 
summation of after-effects, it was first necessary to obtain satisfactory proof of the 
summation of two successive nerve-organ responses produced by two successive 
excitations of its nerve. It was found that the results were not satisfactory if the 
second stimulus followed the first at a very short interval, and was applied to the 
same portion of the nerve. It appeared that for •03" to '0i" after the passage of the 
exciting induction current the excitability of the nerve at the exciting electrodes was 
lowered, and the second stimulus, if occurring in this interval only, produced a small 
inadequate response of the organ. This difficulty was got over by using two pairs of 
platinum exciting electrodes, and exciting different parts of the same nerve. The 
exciting electrodes may be indicated as X x and. X 3 . Of these, X x was 35 nuns, from 
the organ, X 3 45 mms., the length of the whole nerve being 55 mms. The trans¬ 
mission time along the intervening 1 centime of nerve is probably not more than ‘002". 
The spring myograph was used for the production of the induction shocks, being 
placed in the primary circuit of the induction apparatus connected with X l5 and K 3 in 
that connected with X 3 . The traveller could be made to break K x or K 2 only, or K x 
and Ko successively. Although the induction shocks were made equal as far as the 
galvanometric reading of the deflection caused by their passage through it allowed, 
it will be noticed that excitation at the more centrally situated electrode gave a feebler 
response than that produced by the one situated nearer the middle of the nerve trunk. 
Excitation at X l5 G. . 
Deflection. 
+ 95 
95 
...... . 
+ 60 
59 
X x and X 3 , K x being at 0 and K 2 at *03", G. 
+ 178 
59 
•09" 
99 99 59 5 ) 59 
+ 160 
55 
•01" 
55 5 5 95 5 9 59 
+ 122 
55 
X x only, G. . 
+ 80 
95 
-^•2 tt it .. 
+ 54 
55 
X 2 and X 2 , K x at 0. K 2 at '005", G. T g-y . 
+ 111 
55 
55 55 55 55 ... 
+ 106 
55 
5 5 5 9 ^ 55 0 55 ... 
+ 75 
