INDUCED MUSCULAR CONTRACTION. 113 



was discovered by Matteucci, in experimenting upon nervous 

 and muscular irritability, which has been called " induced 

 muscular contraction." 1 It was found that if the nerve of a 

 galvanoscopie frog's leg (the leg prepared with the nerve 

 attached in the way already described) be placed in contact 

 with the muscles of another leg prepared in the same way, 

 galvanization of the nerve giving rise to contraction of the 

 muscles with which the nerve of the first leg is in contact 

 will induce contraction in the muscles of both. This ex- 

 periment may be extended, and contractions may thus be in- 

 duced in a series of legs, the nerve of one being in contact 

 with the muscles of another. This illustrates the great deli- 

 cacy of the galvanoscopie frog's leg, as it will indicate a cur- 

 rent due to a single muscular contraction, which does not 

 affect an ordinary galvanometer. It is conclusively proved 

 that the " induced contraction," as just described, is not due 

 to an actual propagation of the galvanic current, but to a 

 stimulus produced by the muscular contraction itself, by the 

 fact that the same phenomena occur when the first muscular 

 contraction is produced by mechanical or chemical excitation 

 of the nerve. 



Galvanic Current from the Exterior to ike Cut Surface 

 of a Nerve. Before we study certain phenomena presented 

 in nerves a portion of which is subjected to the action of a 

 constant galvanic current, it is important to note the fact, 

 discovered many years ago by Du Bois-Reyrnond, that there 

 exists in the nerves, as in the muscles, 8 a galvanic current 

 from the exterior to their cut surface. 3 This fact has been 

 confirmed by all who have investigated the subject of electro- 

 physiology. It has been roughly estimated by Matteucci 

 that the nerve-current has from one-eighth to one-tenth the 



1 MATTEUCCI, Lemons sur les phenomenes physiques des corps vivants, Paris, 

 1847, p. 288. 



* See vol. i., Movements, p. 476. 



8 Du BOIS-REYMOXD, Untersuchungen uber thlerhcke Ekklricitdt, Berlin, 1849, 

 S. 251, ft seq. 



