58 DUBLIN UNIVERSITY 



3rd. In order to set aside the supposition that these muscular con- 

 tractions might be the result of chemical or mechanical irritation ap- 

 plied to the extremities of the nerves, it became necessary to devise a 

 modification of the foregoing experiments : for although many irritants 

 — such as turpentine, croton-oil, ammonia, friction with a nettle-leaf, 

 &c. &c. — were applied to the nerves without producing any effect like 

 that obtained from the Actinia, it seemed still possible that the contrac- 

 tions might be due to some other agent than electricity. 



The following experiment seems to remove all doubt : — A piece of 

 copper wire, a few inches long, was coated with sealing-wax, except 

 about half an inch at each end. The ends were rubbed clean with sand- 

 paper : one of them was thrust into the lower part of the spinal canal 

 of a frog, prepared as in the last experiment ; while the other, which 

 was to be offered to an Actinia, was passed into a portion of the frog's 

 intestine, put on like a glove, — for the Actinia does not seize vigorously 

 metallic substances. 



The limbs of the frog, with the nerves and vertebrae attached, are 

 laid on a piece of board, while the copper wire, which is curved, arches 

 over the edge of it, so that the end covered with frog's intestine can be 

 readily brought within reach of the Actinia. Having waited for a few 

 moments until the muscular contractions excited by thrusting the wire 

 into the spinal-canal have ceased (and they are in general very tran- 

 sient), the board is placed floating on the water, and the frog's intestine 

 offered to an Actinia. Muscular contractions ensue, perhaps not so 

 promptly, certainly not so vigorously, as in the former experiments ; 

 but, nevertheless, easily to be recognised, and unmistakable. They com- 

 mence in the thighs, and, as in the former case, extend to the calves, 

 and then the toes move actively. This last experiment has been modi- 

 fied in a variety of ways; but the same result has been generally obtained. 

 Perhaps the best modification of it is, to use a piece of copper wire, having 

 one end coiled so as to form a disk, which is covered with chamois 

 leather ; while the other is sharp-pointed to enter the spinal canal of 

 the frog. The whole, except the surface of the disk, which is to be 

 given to the Actinia, and the point for the spinal canal, are covered with 

 sealing- wax, and the frog's limbs extended upon a thin piece of board. 

 With this arrangement, precisely the same effects were produced as al- 

 ready described. 



It is a remarkable fact, and deserves especial notice, that in all these 



