Having laid bare, and separated from surrounding parts and from each other, the crural artery, and nerve, in the thigh of a full grown frog, I cut out the whole of the nerve between the pelvis and the knee. I then insinuated beneath the artery a thin plate of sealing wax, spread upon paper, and broad enough to keep a large portion of the artery completely apart from the rest of the thigh. The blood still continued to flow, through the whole course of the artery, in an undiminished stream. The artery, thus partially insulated, was touched with silver and zinc, which were then brought into contact with each other; but no contraction whatever was produced, in any muscle of the limb. This experiment was frequently repeated upon several different frogs, both in whom the nerve was, and in whom it was not, divided. The result was uniformly the same. But vivid contractions were produced in the whole limb, when an electrical spark, or even a full stream of the aura, was passed into the artery. It, however, by no means follows from this experiment, that the sanguiferous system of animals bears no relation whatever to the influence discovered by Galvani. I have already shewn, that the heart may be affected by it, and have given reason to believe, that the smallest arteries of the body are not exempted from its action. Should it ever be proved to be an exclusive property of animals, it is not impossible but that even its origin may be traced to their sanguiferous system. ----- Footnote 11: I have not been at the pains to inform myself, who first was the author of this doctrine; but its adoption by Caldani, by Haller, and by Fontana, and by all upon the faith of experiment, was certainly sufficient to give it currency, in opposition to that of Willis, Lower, Kaau, Boerhaave, Laghi, and even of the ingenious Whytt. Footnote 12: Mem. Med. Soc. Lond. vol. iii. ------------------------------------------------------------------------ SECTION IV. _An attempt to investigate the Source from which the respective Powers of Nerves, and of Muscles, are derived._ As yet, the question whence the nerves and muscles of animals derive their respective properties, remains in a state of doubt. By many, the brain has been considered as the source not only of the several energies exerted by nerves, whether appropriated to sensation, to the excitement of muscles subservient to the will, or distributed to organs exempted from its influence; but likewise of that unascertained power, by which muscles contract on the application of a stimulus.