330 



the associated metals. If the silver have been applied to the nerves, 

 and the zinc to the muscles, the irritability of these is increased, in pro- 

 portion to the time they have remained in the chain. By this means, 

 you may revivify, in some sort, frogs' thighs, which will after wards obey 

 an influence that was no longer sufficient to excite them. By allotting 

 the metals differently, applying the zinc to the nerves, and the silver to 

 the muscles, the opposite effect takes place, the muscles which were in- 

 troduced into the chain with the liveliest irritability, seem entirely para- 

 lyzed, if they have remained long in that situation. 



This difference depends, very evidently, on the direction of the galvanic 

 fluid, determined towards the nerves or towards the muscles, according 

 to the arrangement of the metals. It is of importance to be known for 

 the application of galvanism to the treatment of disease. Where the ob- 

 ject is to revive enfeebled irritability, it is better to employ the tranquil 

 and permanent influence of the closed galvanic chain, by distributing the 

 silver and zinc, so that the silver shall be nearest to the origin ot % the 

 nerves, and the zinc upon the muscles of which it is wished to re-excite 

 the torpid or suspended action, than to employ that sudden influence, 

 \vhich in an instant, excites and is gone. Professor Pfafi told me, he had 

 treated successfully a hemiplegia, by placing silver within the mouth, 

 and a plate of zinc on the paralyzed arm; at the end of twenty-four hours 

 of uninterrupted communication, the limb could already exert some slight 

 motions. To diminish, on the other hand, the irritable energy in many 

 spasmodic affections, you must invert the application of the metals, place 

 the zinc as near as possible to the central extremity of the nerves, and 

 the silver on their superficial terminations. 



CLXXIII. Apparatus of Volta, or galvanic pile. Curious to ascertain 

 the relation apprehended by several natural philosophers, between elec- 

 tricity and galvanism, Volta invented the following apparatus, which is 

 described, as well as the effects it produces, in a memoir presented by 

 him to the Royal Society of London. These' effects show the most 

 striking analogy between these two orders of phenomena, as will be seen 

 by a succinct view of them. Raise a pile, by laying successively, one 

 above another, a plate of zinc, a piece of moistened paste-board, a plate 

 of silver; then a second plate of zinc, Sec. till the pile is several feet high; 

 for the effects are stronger the higher it is: then touch at once the two 

 extremities of the pile with the same iron wire: at the instant of contact, 

 a spark is seen at the extremities of the pile, and often, at the same time, 

 luminous points, at different heights, in places where the zinc and silver 

 touch. Tried by the electrometer of Coulomb, the extremity of the pile, 

 which answers to the zinc, appears positively electrified; that which is 

 formed by the silver, gives, on the contrary, indications of negative elec- 

 tricity. 



If, after wetting both hands, by clipping them in water, or still better 

 in a saline solution, you touch the two extremities of the pile, you feel in 

 the joints of your fingers and elbow, a shock followed by an unpleasant 

 pricking. 



This effect may be felt by several persons holding hands, as in the Ley- 

 den experiment; it is the more sensible, the composition of the chain be- 

 ing in other respects the same, as the chain consists of fewer people, and 

 a they are better insulated. 



Notwithstanding this great resemblance of the effects of galvanism to 

 those of electricity, it differs from it essentially in this, that the voltaic 



