PEOFESSOE MATTEUCCI’S ELECTEO-PHYSIOLOGICAL EESBAECHES. 
367 
I shall not, as already said, enter here into particular considerations as to the pro- 
duction of secondary polarity in certain bodies more or less analogous to nerves, and which 
physically may be regarded as a solid porous mass the cavities of which are full of a 
conducting liquid. The general conditions required for the development of the secondary 
electromotor power of nerves leave no doubt as to the interpretation of this pheno- 
menon : in the points of a nerve touched by the electrodes of a pile, the products of 
electrolysation are accumulated, and from thence spread through the tissue more or less, 
according to differences of its structure and chemical composition. The direction of the 
secondary current in a nerve is the same as that which is obtained after having sent a 
current through a strip of paper or flannel steeped in a weak saline solution, or, still 
more simply, by wetting two points of this strip, namely that which corresponds 
to the negative pole with an acid, the other, corresponding to the positive pole, with 
an alkaline solution, and then closing the circuit by touching with the extremities of 
the galvanometer either two intermediate points, or two points outside of those traversed 
by the current. 
The object of this memoir is, I repeat, the study of secondary electromotor power in 
nerves, with a 'view to its application to electro-physiology. The principal experiment 
succeeds perfectly on the entire nerve of a living animal. It is easy to lay bare on a 
rabbit or fowl a long piece of the sciatic nerv^e, and to subject this nerve to the passage 
of a current ; when the points of the nerve which have been traversed by the current are 
put in contact with the cushions of the galvanometer, currents owing to secondary 
polarities are immediately obtained. 
By employing the differential method already described, I have also been enabled to 
prove that the secondary electromotor power of nerves is independent of their state 
of vitahty. Thus I have compared two sciatic nerves of fowls, the one taken the 
instant the animal is killed, the other four days after death. These nerves, after being 
cut exactly of the same length, were placed one after another in the same conditions, 
and traversed by the same current for an equal time, after which they were laid on 
the gutta-percha holder and in opposition : no sign of differential currents was obtained. 
I take the sciatic nerve of a sheep, measuring 210 millims., and lay its extremities on 
the electrodes of the pile. It is easy to imagine, without the aid of a flgure, how a com- 
mutator may be employed in this experiment in order to close the circuit upon the nerve, 
either with the pile or with the galvanometer, by a rapid movement of the instrument. 
With the aid of this commutator, in a very small fraction of a second I have sent a current 
of from eight to ten of Grove’s elements through this long nerve, and this has sufficed to 
develope the secondary electromotor power in all points of the nerve. I have frequently 
repeated this experiment, touching successively different points of a long nerve with the 
extremities of the galvanometer kept at an equal distance. I obtained a secondary 
current in aU these points, but as to intensity the results were not constant. 
As far back as the time of my first experiments, I had observed that the secondary 
current obtained between two given points of the nerve differed according to whether 
