gination of the superficial as well as of the more sober observer has always sought in electricity a clue to most, if not all, of the functions of the body. Some, indeed, have gone the dangerous length of regarding electricity as the principle of life itself, and have dared to place it on a level with the divine essence, which, emanating from the Creator, constitutes what, for want of a better name, we call vitality. These pretensions have been given to this agent from its effects when made to traverse the muscles of recently killed animals, but more particularly when conveyed along the spinal nerves of a recently executed malefactor. This, in the hands of Dr. Ure, in his celebrated experiment upon the murderer Clydesdale, worked on the dead but yet warm corpse a horrible caricature of life; by calling into violent contractions the muscles of the face, all the expressions of rage, hatred, despair, and horror, were depicted upon the features, producing so revolting a scene that many spectators fainted at the sight. But this experiment on the recently executed murderer, striking as it was, merely afforded an additional proof of the susceptibility of the muscles to the stimulus of the electric current; and, when divested of the dramatic interest investing it, becomes not more remarkable than the first experiment of Galvani on the leg of a frog.

E

Secretion and nervous agency have always been the favourite phenomena which electricity has been called in to explain, and with some considerable appearance of probability. Dr. Wollaston, thirty-six years ago, first suggested from the resolution of salts into their elements under the influence of feeble currents, that secretion depended essentially upon the electric state of the secreting glands; he thus regarded the kidneys as constituting the positive, and the liver the negative, electrodes of the electric apparatus of the body. A curious anecdote is related of Napoleon, who is said by Chaptal to have remarked, on seeing the voltaic battery of the French Academy in action, "Voilà, l'image de la vie: la colonne vertébral est le pile, la vessie le pole positif, et le foie le pole négatif." We must admit that a great hiatus exists in every argument which assumes that nervous force and electricity are identical, from the fact that, delicate as are our tests for this agent, it has never been actually detected traversing the nerves. It has indeed been stated that on connecting needles plunged in the nerves of a rabbit with the galvanometer, and exciting the muscles of the limb to contract, currents have been detected. Others observers of high repute have stated that a steel needle plunged in a nerve becomes magnetic during the contraction of the muscle it supplies. Both these statements have

been rigidly tested, and have been found utterly unsupported by the results of careful experiment. These failures must not, however, be admitted as quite conclusive against the existence of electricity in the nerves, although their structures are by no means such good conductors as some other of the animal tissues; for it has been well remarked by Dr. Todd and Mr. Bowman, in their elegant and elaborate work on physiological anatomy, that the insertion of needles into the nerves is not a sufficiently delicate means for collecting electricity, if such exists, for they can scarcely be expected to pierce the nerve-tubes, but would sink in between them and the central axis, from which they would be separated by the insulating matter of Schwann. I shall, however, have again occasion to return to this question.

I dare not occupy your time by an allusion to all the hypothetical notions which have been promulgated regarding the part played by electricity in the animal economy; still there are two or three which, as well from their ingenuity as from the talent of their authors, well deserve a passing notice. Among these, the supposed action of electricity, as the agent which, by traversing the nerves, induces the contraction of muscle, a theory announced by Prevost and Dumas, stands foremost. It was assumed by these philosophers that the nervous fibrillæ traversed a muscle in a direc

tion perpendicular to the arrangement of its fibres, forming a series of loops, either by uniting with each other or with a neighbouring nerve. On the influence of the will being directed towards the limb, a current of electricity was supposed to be transmitted along the nervous parallel loops, which would consequently attract each other, and of course, on their approximating, cause contraction of the muscle: this view is evidently founded on the well known fact of currents moving in the same direction attracting each other, which a single experiment will easily demonstrate.

I have here a loose helical coil of thin copper wire, suspended from a metallic support. The free end dipping into a cup of mercury. On allowing an electric current to descend the coil, the convolutions mutually attract each other, and raise the end of the wire from the mercury.

B

Fig. 12.

It is hardly necessary to allude to the objections which may be opposed to this most ingenious

Fig. 12. A, a loose helix of thin copper wire suspended from a support, the free end dipping into a cup of mercury, and communicating by the wire, B, with one plate of a voltaic battery; whilst, by means of the wire, C, the upper end of the helix is in connection with the other plate.

theory; among the most serious is the fact that more recent researches of physiologists have shown that the views of its talented authors are not consistent with a correct knowledge of the organisation of muscular tissue.

The influence of electricity as an agent in exciting the function of digestion, and, indeed, enabling us in some degree to replace the vis nervosa, transmitted by the pneumogastric nerves, by a weak current, has been especially insisted upon by Dr. Wilson Philip. This very indefatigable observer made numerous observations on this matter, and he succeeded in proving that when in a rabbit that had just partaken of a hearty meal, the par vagum was divided on both sides, the food remained in the stomach unaltered, whilst on allowing an electric current to traverse the course of the nerves to the stomach, digestion was effected. This is just what might, from what is now known of the nature of digestion, have been expected, and a very much less energetic current than that employed by Dr. Philip would have been sufficient. For it is now pretty distinctly made out that the function of digestion in the stomach is an action allied to simple solution, of which water a proper temperature, and a free acid, the hydrocloric, phosphoric, or both, are the active agents. The feeble current from a single pair of zinc and silver plates is powerful enough to fur