376 INNERYATION. [CHAP. XI. 



current pass from the nerve to the leg ; but if it pass from the leg to the 

 nerve, contraction will take place on opening the circuit.* 



1. Matteucci's experiments upon the relative conducting power of animal 

 substances were founded, upon a law of derived currents. When a liquid, or 

 any other body, is traversed by an electric current, and the plates of the galvano- 

 meter are plunged into it, there are immediate indications of a derived current, 

 so directed in the galvanometer that the point at which it enters the coil of 

 the galvanometer corresponds to the positive pole of the current which tra- 

 verses the liquid. The derived current is always greater, as the plates of the 

 galvanometer, plunged in the liquid, are more distant from each other. If a cur- 

 rent be made to traverse different substances, which correspond as nearly as 

 possible as regards shape, bulk, etc., the derived current from each will be 

 exactly in the inverse ratio of the conducting power of the substance traversed. 



Pieces of nerve, brain, and muscle, from a rabbit just killed, were selected 

 for the comparative experiments : these were cut so as to correspond as nearly 

 us possible in point of size and shape, and disposed as a chain on an insulating 

 plane. Platinum wires, fixed by sealing-wax to two pieces of cork, which were 

 held apart at a certain distance by a rod of glass which transfixed each of 

 them, were soldered to the wires of the galvanometer, the platinum wires 

 having been previously varnished to within a very short distance of their ex- 

 tremities. A current from twelve cells of a constant battery was now passed 

 through the chain of animal substances. The platinum wires, held always at 

 the same distance from each other, were successively brought into contact 

 with brain, nerve, and muscle, and the deviation of the needle resulting from 

 the derived current in each case was carefully noted. The derived current 

 from nervous matter was always greater than that from muscle ; that from 

 brain greater than that from nerve, denoting a less conducting power in ner- 

 vous matter than in muscle in brain than in nerve. By increasing the dis- 

 tance between the platinum wires, a derived current may be obtained from 

 muscle equal to that obtained from brain ; and Matteucci, from this latter 

 experiment, infers that the conducting power of muscle may be taken as four 

 times greater than that of brain or nerve. 



Another interesting experiment confirmed the results obtained from those 

 just detailed. The current was made to traverse the whole length of a rabbit 

 just killed and flayed ; and the platinum wires, held at a constant distance, 

 were applied successively to different parts, muscles, nerves, etc. : the current 

 was found to traverse all parts, with such difference as was due to the dif- 

 ferent power of conduction of the different substances ; that is, so as to yield 

 a derived current of less intensity from muscle than from nerve, or from 

 nerve than from brain. 



2. To demonstrate the existence of an electric current in the muscles of 

 animals recently killed or living, the following experiments have been 

 adopted by Matteucci. 



If a deep wound be made in a muscle of any living animal, and the nerve 

 of the galvanoscopic frog be introduced into it, so that the nerve shall touch 

 the cut surface at one point, and the outer surface of the muscle at the other, 

 contractions instantly take place on completing the circuit. It is evident that 



* Those who propose to employ the galvanometer in physiological experi- 

 ments should carefully observe the precautions assigned by Matteucci, in the 

 third chapter of his book, to guard against erroneous inferences. 



