308 ELECTEO-PHYSIOLOGY. 



manner independent of the quantity of electricity. Relying upon a physical 

 fact, of which the law and theory are known, I now add that the development 

 of the inducted currents only takes place when the action commences and when 

 it ceases ; which does not, when all other circumstances are equal, prevent the 

 intensity of the inducted currents from being proportional to the intensity of 

 the inductive currents. 



I arrange the experiment to demonstrate the above proposition by placing a 

 prepared frog in one of the dynamometers, using a very weak battery, and in- 

 troducing into the circuit a long column of pure water. In this way we employ 

 the current reduced to the point at which a greater diminution of it is manifested 

 by a diminution of the physiological effect. Having, then, already introduced 

 into the circuit great resistance, when the current is forced to pass through a 

 second nerve we see from the galvanometer that its intensity remains percep- 

 tibly the same. We have thus the certainty that there now passes in the first 

 nerve half the current which passed in the first experiment, when that nerve 

 alone was engaged. And if the experiment is well conducted, if we use in 

 the dynamometer a single muscle, and operate under the same conditions, we 

 shall see that the muscular force is approximately half as much as at first — that 

 is, that the weight attached to the muscle is no longer raised to more than half 

 the former height. We may therefore add that not only is the galvanoscopic 

 frog, properly employed, the most delicate galvanoscope we have, but it is also 

 a galvanometer. 



The third well-established proposition in electro-physiology is this : *♦ That 

 the electric current does not act, or that its action is at least extremely feeble, 

 when it is transmitted across the nerves, instead of traversing them in the di- 

 rection of their ramifications." 



In our present ignorance of the nature of the nervous agent and of its de- 

 pendence on the structure of the nerve, it is impossible to determine precisely 

 the significance of the relation ; but we will admit a priori that it has its 

 significance, and that it must be important. It would detain us too long to 

 recite here the various experiments upon the strength of which the above prop- 

 osition has, since the days of Galvani, been afiirmed or contradicted. After 

 having been long occupied with this subject, I will present to you that which 

 seems to me most conclusive. 



You see fixed upon this cube of wood two parallel plates, one of zinc and 

 one of copper. I place between them a strip of moistened paper so as to form 

 a battery. In effect, when I touch the two plates at the same time with a me- 

 tallic wire, I am certain that the current circulates in this wire, and that at the 

 same time the strip of paper is traversed by as many threads of the electric 

 current all parallel to one another, of equal intensity, and directed from one plate 

 to the other. We have the means of rendering this propagation of electricity 

 in the liquid stratum evident. It consists in dividing the liquid stratum into 

 two parts with a metallic diaphragm, ■^hich is a lamina of platina, and in using 

 for a liquid that mixture of acetate of lead and of copper with which the 

 celebrated electro-chemical exhibitions of our Nobili are found best to succeed. 

 On causing the current to pass, if electrodes be used which have the same 

 section with the liquid stratum, we shall see in a few moments the interposed 

 lamina become colored equally at all j^oints ; and as this color proceeds from a 

 stratum of matter deposited by an electro-chemical effect, and as its color 

 depends, through a most delicate optical property, on the thickness of the 

 deposited stratum, if the current had not the same intensity at all points, wo 

 should be quickly apprised of it by the difierence of color. As this is not 

 so, the filaments of the current which traverse the liquid from one electrode to 

 the other have the same intensity at all points and are parallel. 



Let us return to the former experiment. I prepare the galvanoscopic frog 

 and dispose the long fibre of its nerve on the moistened papei which is between 



•aper wui 



