322 ELECTRO-PHYSIOLOGY, 



practicable to unite several muscular elements in series, forming of tliera one 

 battery, a galvanometer of two or three thou?and coils may suffice, though in 

 more delicate experiments, such as those made on a single muscle and those 

 pertaining to the variation of the muscular electro-motor power under contrac- 

 tion, and the electro-motor power of the nerves, it will be necessary to have 

 recourse to a galvanometer of from twenty to thirty thousand coils. 



In every experiment of animal electricity with the galvanometer there are 

 encountered even to this day causes of error, introduced by the lamince or strips 

 with which the extremities of the galvanometer terminate. In effect the im- 

 provement of this instrument by Nobili led immediately to the multiplication of 

 experiments in electro-physiology, but from want of proper attention to the errors 

 introduced by the use of the lamina just spoken of, the recurrence of erroneous 

 results arrested the progress of this part of physics. The more delicate the 

 galvanometer, so much the more necessary was it to resort to a method which 

 should be guarded against the influence of the extraneous currents attributable 

 to the extremities of the galvanometer and the chemical action of the liquids 

 placed in contact with those extremities. It is not necessary that I should here 

 speak of the experiments of electro-physiology made by using, as extremities of 

 the galvanometer, laminai of iron, silver, or copper, placed directly in contact 

 with the muscles, the brain, or the spinal marrow of a living animal. Perhaps 

 in some of these experiments the effects obtained by the galvanometer should be 

 attributed to the electro-motor power of those parts, but most frequently the un- 

 certainty of the direction and the variable inten^ty of the currents obtained 

 under equal circumstances depend either on the secondary polarity or the liete- 

 rogeneity of the laminre, or on the different action of the animal liquids in contact 

 with them. These uncertainties aud irregularities are nut to be effectually ex- 

 cluded, except Avhen with the muscular batteries we have increased the intensity 

 of the currents, or, better still, when we shall have succeeded in entirely elimi- 

 nating the secondary polarity of the laminae of the galvanometer. 



It is easy to understand the method of the muscular batteries. For the present 

 the muscular element which we are considering is the frog prepared after the 

 method of Galvani, and used in the experiments of Nobili. We will suppose 

 that we have a certain number of these frogs possessing about the same degree 

 of vivacity and similarly prepared. We stretch them on an isolating surface, 

 arranging them in battery — that is, placing the legs of one frog in contact with 

 the legs of the succeeding frog. The extremities of the galvanometer used at 

 first were two equal lamina? of platina soldered to copper wires ; each of which 

 laminse has an isolating handle of ivory or gutta-percha, and is covered with a 

 coating of sealing-wax, leaving exposed only a small and equally extended por- 

 tion of their surfaces. The two laminse must have been first cleansed with 

 potassa, then plunged in a diluted acid, then several times in distilled water, and 

 finally left immersed for a considerable time in this liquid, or in a solution of 

 marine salt. In this way we succeed in rendering the laminse homogeneous, and 

 in divesting them of currents ; if agitated too much, or unequally immersed in 

 the liquid, currents again make their appearance. 



The frogs being arranged, as already shown, in battery, their two extremi- 

 ties — that is, the nerves on the one hand and the legs on the other, are immersed 

 in little cavities filled with distilled or salted water. Having succeeded in ob- 

 taining homogeneity in the platina laminaj of the galvanometer, we close the 

 circuit of the muscular battery by immersing them in the extreme cavities of 

 this battery. We have thus a current which, by employing eight or ten elements 

 and a galvanometer of but two thousand coils, is sufficiently strong to make the 

 needle deviate a full quadrant. It may be thus demonstrated that the deviation 

 increases with the number of the elements, and that the direction of the current 

 obtained by this battery is independent of the nature of the liquid in which are 

 plunged the extremities of the battery, These results have, for the first time, 



