_Experiments in which the Crural Arteries of Frogs were tied as near to the Trunks of their Bodies, as where the Nerves had been divided in the former Experiments._ EXPERIMENT I. Both crural arteries of a full grown frog having been laid bare, one of them was tied. The leg, in which this was done, became instantly weaker than the other, and rather dragged when the animal was put into water. The frog, however, could still jump about with great agility. Four hours after this operation, it was killed by crushing its brain. It continued to move its legs spontaneously, when touched, during more than two days after this, and contractions were excitable by the application of the metals for two days longer. Sometimes it appeared rather doubtful, which leg contracted most vigorously, but, in general, the leg in which the artery remained free did so, and contractions could be excited in it, more than an hour after every means to excite them in the other leg had failed. EXPERIMENT II. Ligatures were passed round the crural arteries of two other frogs, and one of them was suffered to live thirty six hours afterwards, before its head was crushed: the other four days. In these, the disproportion between the vigour and continuance of the contractions in the compared legs, was so much greater than in the preceding experiment, as to leave no doubt of the effects produced by tying an artery. The leg, whose artery had remained tied four days, never contracted near so strongly as its fellow, and contractions had ceased to be excitable in it, upwards of twenty hours before they had ceased in the leg, whose artery had not been tied. From these experiments, it appears decidedly, that a much greater detriment to that condition of a limb, upon which contraction depends, is induced by interrupting its circulation, than by intercepting its communication with the brain. But still, as the effects arising from the interception of the influence of the brain, and of the circulation, were not compared with each other in the same but in different animals, whose age, relative strength, &c. might possibly differ, I thought proper to repeat the comparison, in the following manner. _Experiments in which the Sciatic Nerve was divided on one side, and the Crural Artery tied on the other._ EXPERIMENT I. I divided the sciatic nerve of one leg, and tied the crural artery of the other, in a large frog. Scarcely any blood was lost in doing either. Two days after this, I strangled it. During the first 24 hours, the leg, in which the nerve had been divided, appeared to contract with most vigour; after this period, the difference between them became more doubtful; but the contractions were at no time stronger in the leg, whose artery was tied, than in that whose nerve was divided. EXPERIMENT II.