LECT. XIV. XV. INDUCED CONTRACTIONS. 275 



any other substance, it rarely happens that induced con- 

 tractions are wanting. We are able to say as much of the 

 induced contractions excited by a species of tetanus, which 

 the frog suffers when it has been for a long time submitted 

 to the passage of the inverse current at the time of opening 

 the circuit. 



We must, therefore, confine ourselves to saying that the 

 easiest method of observing the induced contraction is that 

 of exciting the inducteous contraction by the passage of a 

 current in the lumbar plexuses of the frog prepared in the 

 ordinary manner. 



On this ground I have generally made use of the current 

 to excite contractions in my experiments. I have taken 

 every precaution to prevent the galvanoscopic frog, or the 

 thighs of the inducteous frog, from carrying off* a portion 

 of the same current. The most sure method is that which 

 consists in almost completely filling a common plate with 

 turpentine, and placing the frog thereupon. It is needless 

 to add that this substance should be sufficiently thick to 

 prevent the frog from being submerged. Precaution also 

 should be taken in preparing the galvanoscopic frog, to 

 detach from the nerves all the muscular shreds, and to 

 cleanse them thoroughly from blood, by means of blotting 

 paper. 



Whatever be the arrangement of the nerve of the gal- 

 vanoscopic frog, relatively to the muscular fibres of the in- 

 ducteous thighs, the phenomenon of induced contraction is 

 always manifested : thus, in some cases, I have stretched 

 this nerve parallel to the fibres of the muscles ; in others I 

 have arrranged them normally to these same fibres ; or, 

 lastly, I have folded them zig-zag, and yet induced con- 

 tractions have been constantly produced in every case 

 without any perceptible differences. They are also obtained 



