496 PROFESSOR MATTEUCCl’S ELECTRO-PHYSIOLOGICAL RESEARCHES. 
and that more or less rapidly, according- to the intensity of the current, when it cir- 
culates through the nerve from the centre to the periphery (direct current). The 
excitability, on the contrary, is preserved and increased by the passage of the same 
current in a contrary direction, that is to say, from the periphery towards the centre 
(inverse current). 
2. These variations in the excitability of the nerve, produced by the passage of the 
current, tend to disappear more or less rapidly on the current ceasing. If the nerve 
is taken from a living animal, or from one in which life is but just extinct, so that its 
excitability is very great, these variations only last as long as the current continues 
to pass ; while they survive the cessation of the current by from one second to ten 
seconds or fifteen seconds, if the nerve has already lost some of its excitability. 
3. If the same current be made to act upon a mixed nerve, the contraction which 
occurs on the first moment of its introduction is very different, according to its di- 
rection : the direct current always occasions a stronger contraction than that which 
is due to the inverse current. 
In another memoir, which will be a continuation of the present, I propose to in- 
vestigate, as far as is possible, the cause of this diversity of action of the current ac- 
cording to its direction in a nerve. The conclusions drawn above will, I hope, suffice 
for the present to form a much ’simpler theory of the physiological action of the elec- 
tric current than that we have at present, if it be true that we have any at all. 
All are aware that a spark is emitted on the instant the circuit of a pile is closed, 
and again on breaking the circuit. It is also well known that the spark emitted on 
breaking the circuit increases if the circuit is composed of an electro-magnetic spiral 
with its cylinder of iron. Let it be remembered that there is no sign of the current 
passing when the circuit continues closed ; to produce contraction the circuit must 
be broken or closed anew. The simplest idea then which we can admit, and which 
is demonstrated by experiment, is that muscular contraction is excited in every 
case by the electric spark. That which might perhaps have appeared to be in oppo- 
sition to the admission of this idea, is the fact of the frog contracting from very 
feeble currents. It is very easy to overthrow this difficulty. In fact, I may dis- 
pense with any further repetition of experiments by recalling Volta’s opinion in 
support. Immediately after Galvani’s first discovery, Volta applied himself to the 
study of the action of the discharge of the jar upon the nerves of frogs and other 
animals ; and in his very first memoir upon Animal Electricity, he declares that the 
prepared frog is without comparison the most sensitive electrometer we possess. In 
one of his experiments he found that a charge at all times sufficient to excite con- 
tractions could not be estimated at the -^jth of a degree of his straw ’electrometer. 
Indeed it is very easy to verify these assertions of Volta. My plan is as follows: — I 
take a small Leyden jar having about thirty square centimetres of coating, and after 
having charged it to saturation, I discharge it four tjmes successively with a metallic 
rod, so as at last to produce no perceptible spark. In the same manner, at this 
