This terrible serpent is found in the province of Ceara, whence it was brought to Rio Janeiro. This species generally attains a length of from four to five feet but the animal from which the poison was taken for our provings, was three feet long. Its oval-triangular head one half of which is provided with shields, shows a round depression in front of the eyes, which are covered with a large elliptical shield, serving as a lid. The body is big, conical, its movements are sluggish; its upper surface is covered with scales, the dorsal scales being keeled and somewhat lanceolate, the scales of the tail being quadrangular and smaller. The belly is provided with one hundred and seventy large transversal plates; there are twenty-five plates belonging to the tail, the three first of which are divided in shields. The extremity of the tail is furnished with seven or eight capsules of the consistence of parchment which, when agitated, produce a shrill sound. The color of the crotalus is a yellowish-brown, much lighter under the belly, with twenty-four or twenty-six regular long rhomboïdal lines on each side of the back. When irritated and during the excessive heat, the crotalus spreads a very fetid musk-like odor. The molar teeth which are few in number, but long and excessively poisonous, are inserted in exceedingly dilatable jaws. Every body knows that the poison of this reptile acts with a frightful intensity; and it was not without great danger that Doctors Mure and Martins succeeded in obtaining a few drops of it, by compressing from the living animal the gland which secretes it. FIRST EXPERIMENT. 1. First day: Heavy pain in the back part of the orbit, and at the left eyebrow.—Second day: Pain under the right orbit and at the forehead, right side.—Third day: Dry cough with tickling in the throat, at night.—Fourth day: Headache extending over the forehead and then the rest of the head. 5. Fifth day: Smell all day like that of the crotalus, insipid, nauseous, like the odor perceived in a hospital. Sixth day: Lancinations in various parts of the body.—Seventh day: Contraction with pressure at the right eyeball which felt as if drawn out.—Eighth day: Yellowish diarrhœa.—Ninth day: Pain in the middle of the forehead. 10. Tenth day: Rheumatic pain in the right shoulder.—Eleventh day: Rheumatic pain in the left wrist.—Twelfth day: Violent cramps in the heel. SECOND EXPERIMENT. (The drug is taken at 10 o’clock in the evening.)