XIV. Those who attempt to determine the velocity of the nervous fluid in a given time, undertake a matter of great difficulty, respecting which nothing certain can be known. Haller rejected the suppositions of those who, comparing the tenuity of the nervous tubes of the heart with the large branch of the aorta, were of opinion, that the velocity of the nervous fluid must be two thousand eight hundred and eighty times greater than that of the blood. This celebrated physician, distrusting hypothesis, had recourse to experiment, and found that the velocity of the nervous fluid would be no less than nine thousand feet in the first minute. But in this determination of the velocity of the nervous fluid there seems to be some difficulty, which perhaps ought to be ascribed rather to the period when that celebrated man lived, than to his want of sagacity or accuracy. Had Haller possessed the means of conveying the nervous fluid with his own hands to different parts at pleasure, he would no doubt have given us some more certain ideas respecting its rapid motion. I resolved, therefore, not to neglect those advantages with which the modern philosophy has been enriched, and to employ very long metallic arcs, by which I could direct the animal electricity as I pleased. A staircase which reached from the top to the bottom of the house, with many windings, presented me with an iron plate, exceedingly convenient for the transmission of animal electricity. A metal wire, brought down from the top of the staircase, was connected with the iron plate, and by these means I obtained an arc, the length of which was above one hundred and fifty feet. When this arrangement was made, the two extremities of this very long arc were applied to the armed nerves and muscles of a frog; and the animal electricity being thus excited, instantly proceeded with so much velocity from the one extremity of the arc to the other, that no difference could be perceived between the time when the frog touched the arc, and that when it began to be agitated. But to show that this result was not owing entirely to the metallic conductor, I employed long ropes dipped in salt water, and always with the same effect. This circumstance seems to prove, in a striking manner, a great similarity between the nervous fluid and common electricity, and to overturn the opinion of Haller, who, according to his calculations, makes the nervous fluid require a second for passing over the space of 150 feet.