286 PROFESSOR MATTEUCCI'S ELECTRO-PHYSIOLOGICAL RESEARCHES. 



ployed the receiver commonly in use for the experiments of electricity in vacuo, or 

 in other gases than air. The two platinum wires are fastened to the metallic rod 

 which moves in the tube in the centre of the receiver ; one of the wires, however, is 

 insulated from the rod by a layer of gum-lac which intervenes where the wire encircles 

 the rod. These two wires are twisted into the shape of a pitchfork, and so diverge 

 from one another, that on pushing the rod down the two extremities enter the ex- 

 treme cavities of the muscular pile (fig. 2.). I rapidly exhausted the air in the re- 

 ceiver, and then connected the platinum wires with the galvanometer. I have re- 

 peated the experiment while the air was exhausted, and immediately after admitting 

 the air again into the receiver. The direction of the current has never varied, nor 

 have I perceived any very great difference in the intensity and duration of the cur- 

 rent in the different modes of conducting the experiment. 



It will be readily understood from the description of the apparatus employed for 

 operating in a vacuum, how easy it was to adapt it to experiments in other gases : 

 I have used hydrogen and carbonic acid. 



I think it important to describe minutely the results obtained in these different 

 experiments. I began with a pile composed of twenty muscular elements, or half 

 thighs of frogs, placing it under the receiver, and I filled the cavities of the pile with 

 well-water, after ascertaining that there was no sign of a current on immersing the 

 ends of the wire in the same liquid. In less than five minutes the frogs were killed 

 and the pile prepared. In performing these comparative experiments, I have made 

 use of frogs caught on the same day and in the same pool. In all these experiments 

 the circuit was kept closed, and the duration of the current in the galvanometer ob- 

 served for several hours successively. The following are the numbers obtained in 

 the different experiments. 



Operating in atmospheric air with a pile of twenty elements of frogs, the deflection 

 in my galvanometer was so strong that the needle reached 90°, oscillated, then gra- 

 dually returned towards 0°. At about 30° the needle begins to be stationary, or at 

 least it retrogrades considerably more slowly than at first. Every ten minutes I 

 noted down the deviations, which are the following: 15°, 9°, 5°, 4°, 3^°, 3J°, 3^°, 3j°. 

 At the expiration of two hours the deflection was the same. The circuit was then 

 broken, and the extremities of the wires immersed in pure water, the current pro- 

 duced was 70°, and its direction was contrary to the first when the circuit was closed 

 with the muscular current. This was evidently the secondary current which at the 

 commencement of my researches I showed to be the cause of the rapid decline of the 

 muscular and proper current in those cases where the circuit is kept closed. I have 

 twice repeated this same experiment with the same results. 



I have constructed a third pile similar to the two already described, which I have 

 put under the receiver mentioned above, and have exhausted the air to that degree 

 of rarefaction that the mercurial column showed only one inch of pressure. I could 

 not attain to a more complete degree of rarefaction on account of the aqueous vapour 



