PHYSIOLOGY OF THE NERVOUS SYSTEM. 



720R 



the nerve of the leg is to be laid upon the mus- 

 cles of either thigh, and if these muscles be 

 excited to contraction by mechanically stimula- 

 ting the lumbar nerves, or the spinal cord, or by 

 passing a galvanic current through the nerves 

 or the cord, the muscles of the galvanoscopic 

 leg will be simultaneously contracted. If a 

 second and a third galvanoscopic leg be pre- 

 pared, and the nerve of the second be laid on 

 the muscles of the first, and that of the third be 

 1 lid upon the muscles of the second, contrac- 

 tions will take place in all three whenever the 

 muscles of the prepared thighs are thrown into 

 contraction. Matteucci, to whom we owe the 

 discovery of this important fact (which he 

 terms induced contraction*) has failed to cause 

 a fourth leg to be thus affected. 



If the galvanoscopic nerve be laid on the 

 muscles of a frog's thigh in which tetanoid con- 

 vulsions have been produced by the cessation 

 of a long continued inverse current, the in- 

 duced contractions will be likewise tetanic.f 



The annexed woodcuts (Jigs. 3986 &; 398f) 

 will serve to show the manner in which these 

 experiments may be performed. 



It is plain, then, that during the contraction 

 of muscles, whatever be the means used to sti- 

 mulate them, a force is evolved capable of ex- 

 citing a nerve laid upon the exterior of the con- 

 tracting muscle to such a degree as to cause 

 contraction of the muscles it supplies. What 

 is this force ? The readiness with which it 

 excites the nerve of the galvanoscopic leg re- 

 sembles the action of electricity, and this view 

 of its nature is favoured by the known fact that 

 during muscular contraction heat is evolved, and 

 in some of the marine animals, light also, ac- 

 cording to the observations of Quatrefages. If 

 heat and light be produced during muscular 



contraction, it is not unreasonable to expect 

 that electricity should be evolved likewise. 

 Matteucci's experiments, however, throw some 

 difficulty in the way of viewing it as such. He 

 finds that this force will freely permeate very 

 imperfect conductors of electricity, whilst it will 

 not traverse substances which are known to con- 

 duct electricity. If gold leaf be placed upon 

 the muscle between it and the nerve, the con- 



Fig. 3986. 



The limbs of a frog prepared according to Gal- 

 vani's method, the nerve of the galvanoscopic leg 

 being laid across the muscles of one thigh. When 

 these muscles are thrown into contraction by any 

 means, mechanical or galvanic, those of the leg con- 

 tract at the same moment. 



Fig. 393c 



The limbs of a frog prepared after Galvani's fashion. In another frog the galvanoscopic leg is 

 prepared, but the sciatic nerve is left in connection with the lumbar plexus and the spinal cord. If this 

 nerve be laid across the thighs of the frog and the limbs be made to contract, contractions will be 

 simultaneously excited in the galvanoscopic leg and also in the other one. It is plain that while the 

 contractions in the galvanoscopic leg are excited by the direct stimulation of the sciatic nerve, those in 

 the other leg are excited through the excitation of the spinal cord by the sensitive fibres of the same 

 sciatic nerve. 



* Phil. Trans. 1845, p. 303. t Id. 1846, p. 487. 



