ELECTRO-PHYSIOLOGY. 309 



the two plates of the battery. If the fibre is disposed transversely, in which 

 direction it is certain there can be no filament of electricity which traverses the 

 nerve parallel to its axis, there will be no contraction seen in the frog when I 

 set the battery in action by touching the two plates with the metaUic wire. And 

 observe that while I thus operate, the whole long nervous fibre is stretched upon 

 the paper and is perpendicularly traversed by the current at all points. 



I now invert the position of the nerve and stretch it, though to a much shorter 

 extent, in such a way that the electric stream traverses it parallel to its length. 

 Immediately contractions ensue, now at the opening, now at the closing of the 

 circuit, provided the current is very weak, or the nerve has already lost a little 

 of its excitability. It is beyond doubt, therefore, that the efiect of the current 

 upon a nerve is null, or at least extremely feeble, when the former traverses the 

 nerve in a direction perpendicular to its length. It is not without importance 

 to remark that whether we conceive the excitation of the nerve by the current 

 to be due to a species of mechanical effect which is propagated towards the 

 muscles or towards the nervous centres, or whether we consider that excitation 

 under the analogy which it may bear to electro-dynamic action in general, we 

 may, to a certain point, comprehend this difference of the action of the electric 

 current according as it is propagated along the axis or perpendicularly to the 

 axis of the nerve. 



Whether we use in making these experiments the discharges of the jar or the 

 inducted currents, when the two electrodes are applied directly on the nerve, 

 now transversely and now along the axis, it may be easily understood how diflS- 

 cult it must be, with this arrangement, to realize the conditions of the experi- 

 ' ment, and how it may happen that the currents should be always very strong, 

 and that there should be always a portion of the electric filaments which traverse 

 the nerve in a direction more or less parallel to the axis. In the mode in which 

 we have operated these causes of error are removed, and therefore this propo- 

 sition may be received as demonstrated by experiment. 



Lecture IV. — Electro-physiological laws. — Effect of the continuous current on the excitability 

 of the nerve. — The inverse current exalts the excitability of the nerve and the direct ex- 

 tinguishes it. — Tetanic contraction produced in a muscle, the nerve of which was traversed 

 by the inverse current at the moment of opening the circuit. — Secondary electro-motive 

 power of the nerves and its application to the phenomena excited by the inverse current at 

 the opening of the circuit. — Action of the current on the roots of the nerves. — Correction 

 of the mode of interpreting the results of Louget and Matteucci with derived currents. — 

 Action of electricity on the ganglionic system. — Medical uses of electricity. — ^Aneurism. — 

 Tetanus. — Cure of paralysis. 



To complete the first part of this course, that, namely, relating to the phe- 

 nomena Avliich the current produces in its passage through the nerves and 

 muscles of an animal either living or recently killed, it remains to consider par- 

 ticularly the action which the current exerts on the properties of the nerve by 

 continuing to pass for a long time through it. On this occasion I shall be en- 

 abled to give an explanation of the electro-physiological phenomena which are 

 manifested at the opening of the circuit; an explanation which, from being 

 founded on known physical laws, constitutes one of the most important ad- 

 vances made in the science of electro-physiology in later times. 



Let us resume the usual preparation of the frog — that is, the frog, after Gal- 

 vani's manner, cleft in the middle and traversed by the electric current from one 

 member to the other. With this arrangement we can have, as was said in the 

 preceding lecture, two nerves derived from the same animal and traversed simul- 

 taneously, one by the direct and the other by the inverse current, and be thus 

 enabled conveniently to compare their state. The experiment may be prepared 

 either by placing the frog astride between two small goblets filled with common 



