ELECTRO-PHYSIOLOGY 303 



magnetizpd are drawn towards one another. It is a well-known effect controlled 

 by recognized laws ; the electric current is generated in the battery when there 

 is zinc which is oxidized. In the muscle, also, there is this oxidation — there 

 is carbon which combines with the oxygen and burns, and through this chemi- 

 cal action there is heat, and therefore force, developed. But what are the mus- 

 cular elements corresponding to the magnetic elements 1 By what laws and 

 with what force are these elements moved, in order to produce the contraction 1 

 Herein couyists the mystery; or, rather, let us call it one of the most subtle of 

 problems which physics and chemistry will one day assist physiology to re- 

 solve. 



After these general propositions respecting the mechanism of contraction ex- 

 cited by the passage of the electric current in the nerves, we shall employ our- 

 selves in the next lecture in studying the relations existing between these elec- 

 tro-physiological effects and the direction of the current, its intensity, and its 

 course in traversing the nerves. 



Lectijre III. — Manner of representing the action of the current in contraction. — Experiment 

 of magnetic attraction within a spiral. — Laws of electro-physiology. — Different etiect of 

 the current according to its direction in the nerves. — Errors introduced into experiments of 

 electro-physiology by derived currents. — Periods of Ritter and ol' Nobili. — Experiments of 

 Masianiui. — Galvanoscopic frog and its use. — Electric excitatioh of the nerve reduced to 

 half when a given current is divided between two nerves. — The current does not act by 

 passing in a nerve transversely. 



The whole of my last lecture was occupied — and I hope not uselessly — in 

 presenting some experiments and general considerations which give us an idea 

 of the mechanism by which electricity, acting on nerves and muscles, produces 

 muscular contraction. Unlike what takes place through the chemical, calorific, 

 and magnetic effects of the electro-current, which depend on the quantity of 

 electricity and on the duration of its action, electro-physiological effects are 

 manifested only during those variations of the electrical state which occur at the 

 closing and opening of the circuit ; that is, in that minute interval of time in 

 which any conductor traversed by electricity is passing from the natural state to 

 the state of electro-dynamic equilibrium and vice versa. Independently of the 

 quantity of electricity, the electro-physiological action is proportional to the 

 velocity with which this variable state of the beginning and of the end of the 

 current is produced, and this explains how the least sparks or discharges of the 

 Leyden jar act strongly on the nerves and muscles, and how their action is 

 diminished or extinguished by causing these discharges to pass slowly through 

 conductors very long and imperfect. 



When the quantity of the electricity and the velocity of the discharge com- 

 bine, we have, as in the case of lightning, the most violent electro-physiological 

 effects. It will be remembered also that the electric excitation of the nerve 

 does not determine muscular contraction, except by previously exciting the 

 chemical action of the muscular contraction. 



Our attention should now be turned to the laws of electro-physiology — that 

 is, to the relations which exist between the physiological effects and the direc- 

 tion of the electrical current in the nerves, its intensity, the physiological properties 

 of the nerves, &c. Few are the parts of physics with which experimentalists have 

 occupied themselves so much as with this, and yet too few are the rigorous and 

 general conclusions at which they have arrived. For this reason I shall abstain 

 from detailing to you all that is known or is supposed to be known on this sub- 

 ject, and which may be more or less confirmed, more or less contradicted in 

 general, but shall restrict myself to the few propositions which have been 

 demonstrated by experiment, and regarding which there is no dispute. 



