ELECTRO-PHYSIOLOGY. 321 



larity. The circuit being left closed, the deviation after some time amounts to 

 nothing, or very little. A frog is then rapidly prepared, the wick is removed, 

 and the frog is substituted by immersing the lumbar nerves in one vessel and 

 the legs in the other. At that instant the frog contracts, and the needle devi- 

 ates by an arc of twenty-five or thirty or more degrees, and settles at a much 

 less angle, which continues eventually to decrease. If the experiment is re- 

 peated on another frog, inverting at the same time its position with respect to 

 the extremities of the galvanometer-, the deviat'on occurs in the opposite direc- 

 tion. Kobili also ascertained, by operating upon two or three frogs similarly 

 prepared and imited in form of a battery — that is, by placing in contact the 

 muscles of one with the nerves of another, that the deviation of the needle in- 

 creased in proportion to the number of the frogs. It results from these experi- 

 ments that, by uniting through a homogeneous arc the nerves and muscles of a 

 prepared frog, there is established in this arc a direct electrical current, so that 

 the muscles represent the zinc, and the nerves the carbon or jilatina of a voltaic 

 pair, by which the current is directed in the animal from the muscles to the 

 nerves, or from the feet to the head of the frog, as it is customary to say. This 

 current was, according to all analogy, the cause of the contraction observed in 

 the experiment of Galvani. 



Nobib did not sufficiently vary his experiments to be enabled to arrive at an 

 exact interpretation of the fact which he had discovered, and, led by a false 

 analogy, he overlooked the true origin of the electricity of which, however, ho 

 had rigorously demonstrated the existence in animals. lie imagined that the 

 nerves and the muscles, by their different structure and composition, were bodies 

 which parted unequally with the water by evaporation, whence they must have, 

 as he reasoned, since they are exposed to the air, a different temperature, from 

 which he inferred that the current discovered in the frog was a therm )-electric 

 current between the nerve and muscle, and, therefore, independent of the living 

 organism. A slight consitleration, however, of the conditions under Avhicli his 

 experiment was made, will satisfy us how dissimilar and even opposite they are 

 to the conditions in which thermo-electric currents are produced ; and, more- 

 over, wo shall presently see that the true electro motor in the experiments of 

 Nobili, as in those of Galvani, (which do not differ except through the addition 

 of the circuit of the galvanometer and the electricity of the frog being proved 

 not only by the contraction, but also by the deviation of the magnetized needle,) 

 is not formed by the union of the nerves and muscles, but by the various parts 

 of the muscle alone. 



I shall endeavor to show the laws of the muscular electro-motor by simple 

 and exact experiments, and must, therefore, premise a description of the instru- 

 ments and methods used in these experiments. 



You are already acquainted with the preparation of the galvanoscopic frog 

 and its use. The leg of a frog rapidly prepared, and with which a long nervous 

 filament remains united, is placed upon a slip of gutta-percha ; the nerve is to bo 

 slightly dried by placing it upon a sheet of felt paper, and then the piece of 

 muscle of which we would ascertain the electrical state is touched with two 

 points of this nerve. By repeating this experiment several times, changing the 

 points at which the muscle is touched by the nerve, and observing the instant 

 at Avhich tlie contraction occurs, we may determine with some certainty the di- 

 rection of the current. In such an experiment we may also use the whole frog 

 divided in half, after the manner described in former lectures, and with this, if 

 the current is sufficiently intense, it is still more easy to discover the direction 

 of the current, because commonly one of the members, that, namely, which is 

 traversed by the direct current, contracts when the circuit is closed, and the 

 other at the opening. 



The galvanometer of very fine and long wire, with a good magnetic system, 

 is the essential instrument for the researches of electro-physiology. Since it is 

 21 s 



