Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

voltaic battery, Ave see the astatic needle deflected to a certain degree by the passing current. If we now lengthen the con- ductors by interposing copper or even silver wire of a given length, and then again of twice that length, and then again of twice the length of the latter, we shall find from these ex- periments, that the needle of the instrument is less and less deflected, according to the length of the conductors, although of the very best material. The human living body conducts all electric currents ten to twenty times better than pure cold water. This is supposed to be on account of the warm salt water it contains. But I am more and more inclined to believe that this is owing to the arrangement of these different fluids in the different cells and tissues of the living organism, which are separated only by the thinnest membrane, and being provided with nerves, not only have a tendency to electric action, but pos- sessing an actual, perpetual minute action, which, to my mind, serves for the artificial current conduction, much as Professor Morse's registering battery helps the working of the wires; per- haps more, as the aurora borealis helps the conductibility of the telegraph wires. The epidermis is, in this case, probably, the greatest hinder- ance to all currents of electricity ; but this can be greatly coun- terbalanced by ivet electrodes. There is an absolute difference in the conductibility of different persons, and even of the same individual at different times. In a group of persons, a single one may be struck by lightning, while all the others remain untouched. But this is not as yet satisfactorily explained. The human body, then, after all, is not in effect a good conductor of electricity, as can be proved by the galvanometer. To test this, the resistance is first determined of the given entire circuit, of say a bearable, but appreciable battery, such as twenty to thirty Daniell's elements afford, by bringing together the two poles in good contact, including nothing but the galvanometer. The degree of resistance from the connecting wires of the batteries, the conductors, and the instrument together, as marked on the dial, is first noticed, and taken for \mit or zero. Then the limb or individual is interposed between the wet electrodes, which 11*