ELECTRO-PHYSIOLOGY. 297 



It is not so with the electro-physiological action. If the circuit of a hattery 

 be closed with wet hands, or if the current be made to pass into a prepared frog, 

 whether in the muscles or nerves alone, or in both muscles and nerves of the 

 frog or of any animal living or lately dea(], it will always be found that the con- 

 traction and the pain are produced at the first moment when the electricity begins 

 to pass, and that none is any longer felt or observed while the circuit remains 

 Closed. It is not, then, the quantity of electricity, not, as we might say, the 

 passage of the current in the nerves and muscles, which occasions those effects. 

 If, instead of keeping the circuit in which the frog is included closed, the pas- 

 sage of electricity is after a certain time interrupted, the signs of pain and the 

 contraction are then manifested anew. And if, to effect these closures and open- 

 ings of the circuit, a wheel of interruption be employed, the frog will be seen to 

 contract and its muscles to be relaxed in succession at each passage and each 

 interruption of the current. If these alternations be very rapid the frog is seized 

 with tetanic contractions, which shortly destroy the nervous power'and kill the 

 animal. In this way it is possible with certain kinds of apparatus of induction 

 to give even with a very weak current a series of repeated shocks which shall 

 kill large and strong animals. This effect, therefore, is not owing to the quantity 

 of electricity, but rather to the variation of the electric condition which arises in 

 the nerves and muscles of a living animal at the moment of opening and closing 

 a voltaic circuit. This variable state of the electric tension of a voltaic con- 

 ductor which was heretofore admitted by physicists as a consequence of the 

 well known theory of Ohm respecting the battery, is now placed beyond doubt 

 by experiments made on the long wires of telegraphs. When the circuit of a 

 battery is closed by touching its poles with a conducting arc, we know that the 

 electric state, and hence the flow of electricity, does not attain at all points and 

 at the same instant that permanent degree at which it arrives after a certain 

 time, though a very minute one, but which has yet been measured by operating 

 upon long telegraphic circuits. We now know that in a circuit of iron wire 500 

 or 600 kilometres in length, between the moment in which the circuit is closed, 

 and that in which the intensity of the electric current is perceptibly constant at 

 all points, there is an interval of time which has been found to be 15 to 18 

 thousandths of a second. This is the duration of the so-called variable state, 

 which, according to the nature of the circuits and the apparatus which give the 

 electric discharge, continues for a greater or less time. The electro-physiolo- 

 gical action seems to depend on the velocity with which the permanent electric 

 state is established in the nerves and muscles of the living animal : the less the 

 duration of this variable state, so much the greater is the electro-physiological 

 effect. We know that in the discharges of the Leyden jar or in the sparks of 

 the electric machine, the quantity of electricity is extremely small. By com- 

 paring the heat developed in a wire of platina by a discharge of the Leyden jar, 

 which lasts for a very minute space of time, less perhaps than 2T000' ^'^^^ ^^^ 

 heat obtained by a small battery which with the same wire lasts for several 

 minutes, the conclusion has bees* arrived at, if not with absolute rigor, certainly 

 with great probability, that the quantity of electricity developed by the battery, 

 in proportion to the very small quantity of zinc oxidized, is many times greater 

 than that which constitutes the lightning of a heavy storm. 



It is in our power at present, if not to measure the smallest duration of the 

 electric spark, at least to determine the limit — that is, a quantity still less than 

 that which represents the actual duration of the spark. Nor must I omit to 

 make mention of that highly ingenious application of the measurement of very 

 small intervals of time for the correction of certain indications which, through 

 the persistence of the images on the retina, assume for us a false appearance. 

 When a body revolves with a certain velocity, instead of seeing it at the suc- 

 cessive points which it occupies, we see it in the form of a continuous ring, 

 because our eye still retains the impression of the body in a certain position for 



