I CUT one hole in the fore and upper part of the Cranium and Dura Mater of a Frog, and another in the back part of the lowermost Vertebræ, and then injected, from the one hole to the other, a small syringe full of water, in five ounces of which one ounce of Opium had been infused for three days. The infusion, by this means brought into contact with the whole surface of the Encephalon and Spinal Marrow, produced almost instantly universal convulsions; and, in less than two minutes thereafter, the Animal was incapable of moving its body from the place where it was laid. A quarter of an hour thereafter, I found the Heart beating twenty-five times only in the minute; and so feebly, that it could not entirely expel the Blood. When, half an hour thereafter, the Sciatic Nerves were pinched, a light tremor only was excited in the Muscles of the Leg; and Animal Electricity produced but feeble twitchings of the Muscles. THE infusion of Opium, injected in the same manner in Rabbits and in a Pig, produced similar effects. I HAD long ago[1] observed, that an infusion of Opium, poured into the Cavity of the Abdomen of a Frog, after cutting out its Heart, occasioned, in a few minutes, convulsions of its hind Legs. I have since found, that, after cutting off the Head, and cutting out the Heart of a Frog, its hind Legs are considerably weakened by pouring an infusion of Opium into the Cavity of its Abdomen. ALTHOUGH an infusion of Opium poured into the Auricle and Ventricle of the Heart of a Frog, instantly renders that Organ incapable of contraction, and, even after the Aorta has been previously cut, occasions convulsions of the Legs, yet I have not found that by Opium applied to the Brain, the Spinal Marrow, the Heart, or Abdominal Viscera, the Muscles of the Legs were so entirely killed as not to perform some motion when their Nerves were pinched, or when they were acted on by Animal Electricity. AFTER taking out the lower half of the Spinal Marrow, and likewise cutting transversely all the parts at the Pelvis, except the Crural Arteries and Veins and Lymphatics, which probably accompany them, I found that an infusion of Opium, applied to the Skin and Muscles of the Legs, affected the superior parts of the Body[2]: more probably, in my opinion, by absorption, than through any minute remanent branches of the Nerves, especially as I do not find, on laying the Vessels so prepared over a gold probe, and touching with it Zinc laid under the Spine, that convulsions of the Legs can be excited. At the same time, the quantity of Opium absorbed is so small, that I could not distinguish its smell or taste in the Blood; nor did I find these distinguishable, in other Experiments, in which the Frogs were violently convulsed after applying the infusion to the surface of their Skin. ANIMAL Electricity or different metals applied to the Head of a Frog, or to any part of its Spine above its sixth Vertebra, do not occasion convulsions of its hind Legs.