PHYSIOLOGY OF THE NERVOUS SYSTEM. 
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 
laid 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.t 
The annexed woodcuts (figs. 398b & 398c) 
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 
The limbs of a frog prepared after Galvani’s fashion. 
prepared, but the sciatic nerve is left in connection with the lumbar plexus and the spinal cord. 
Fig. 
720R 
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. ° 
398c. 
In another frog the galvanoscopic leg is 
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 
Sviatic nerve. 
* Phil, Trans, 1845, p. 303. 
+ Id. 1846, p. 487. 
