CHAP. XI.] MATTEUCCl'S PHYSIOLOGICAL RESEARCHES. 381 



parts are placed on an insulating plane. If the muscles of one leg are made to 

 touch the other thigh, contractions ensue ; but not so if the leg of one side 

 touch the leg of the other. Or the same effect may be produced by bringing 

 the different parts of the limbs into connexion by moist paper or cotton ; or, 

 if the galvanometer be employed, signs of a current are afforded, by touching 

 a thigh with one pole, and the opposite leg with the other. 



In these experiments, when the frog is lively, contractions are produced, in 

 touching the muscles of the thigh with those of the leg, as well on opening as 

 on closing the circuit. But when it has become weak, contractions take place 

 in one limb on closing the circuit, and in the other on opening it. 



Matteucci explains the failure in producing contractions by touching corre- 

 sponding parts, on the supposition, that, under such circumstances, the currents 

 of the two limbs circulate with equal intensity, and in a contrary direction. 

 This he proves by the following experiment: If the frogs' legs, prepared as 

 above described, are severed from each other, and the nerve of one leg and the 

 foot of the other are placed in one capsule filled with water, while another cap- 

 sule receives the other nerve and foot ; the moment the circuit is completed, 

 strong contractions in both limbs are produced. But to the galvanometer no 

 sign of an electric current is afforded when its poles are plunged into the cap- 

 sules. " In this case," says Matteucci, " the currents of the two limbs circulate 

 together, passing equally through the limbs; and if even the parts of the 

 current were to take the courso of the galvanometer, it is easy to see that they 

 would circulate in it in opposite directions, and therefore would produce no 

 deviation. If, on the contrary, the disposition of the two limbs be such that 

 the nerves are placed in one vessel, and the feet in the other, it is easy to see 

 that the two portions of the current which do not circulate through the 

 animal arc, enter the extremities of the galvanometer, and circulate in it in 

 the same direction. It is the sum of these two portions which constitutes the 

 proper current of the frog, which sum is measured by the galvanometer. 



If several frogs' legs be arranged with opposed nerves and feet in the two 

 capsules, the effect upon the galvanometer is not increased. 



Comparative experiments as to the difference of the currents in piles formed 

 of both the lower extremities of frogs, as already described, and in piles 

 formed of an equal number of single extremities, shewed no greater effect 

 upon the galvanometer in the one case than the other. 



From these and numerous other experiments, varied with great ingenuity and 

 skill, Matteucci draws these conclusions: 1, that the complete electromotor 

 element in the current of the frog is formed by one of its limbs that is, of 

 one leg, the thigh, its spinal nerve, and a piece of its spine ; 2, that the cur- 

 rent of one limb circulates by the other every time that, leaving the frog in- 

 tact, a communication is established, in any way, between the two legs of the 

 same frog; 3, that in the experiment by which we detect the current of the 

 frog by the galvanometer, there is never in the wire of the instrument any 

 other current save that which results from the sum of the two portions of 

 the currents of the two limbs which are not discharged from limb to limb. 



It is important to notice that there is no necessary connexion between nerves 

 and muscles in the production of the proper current of the frog. Matteucci 

 shews, by several ingenious experiments, that, although in Galvani's and 

 Nobili's observations, the nerve and muscle were brought in contact, or were 

 made to form conspicuous parts of the arrangement employed in the develop- 



