_a._ A stout and healthy young cat, of four or five months old, was introduced into a large jar of nitrous oxide. For ten or twelve moments he remained perfectly quiet, and then began to make violent motions, throwing himself round the jar in every direction. In two minutes he appeared quite exhausted, and sunk quietly to the bottom of the jar. On applying my hand to the thorax, I found that the heart beat with extreme violence; on feeling about the neck, I could distinctly perceive a strong and quick pulsation of the carotids. In about three minutes the animal revived, and panted very much; but still continued to lie on his side. His inspirations then became longer and deeper, and he sometimes uttered very feeble cries. In four minutes the pulsations of the heart appeared quicker and feebler. His inspirations were at long intervals, and very irregular; in five minutes the pulse was hardly perceptible; he made no motions, and appeared wholly senseless. After five minutes and quarter he was taken out, and exposed to the atmosphere before a warm fire. In a few seconds he began to move, and to take deep inspirations. In five minutes he attempted to rise on his legs; but soon fell again, the extremities being slightly convulsed. In eight or nine minutes he was able to walk, but his motions were staggering and unequal, the right leg being convulsed, whilst the other was apparently stiff and immoveable; in about half an hour he was almost completely recovered. _b._ A healthy kitten, of about six weeks old, was introduced into nitrous oxide. She very soon began to make violent exertions, and in less than a minute fell to the bottom of the receiver, as if apoplectic. At this moment, applying my hand to her side, I felt the heart beating with great violence. She continued gasping, with long inspirations, for three minutes and half; at the end of five minutes and half she was taken out completely dead. _c._ Another kitten of the same breed was introduced into nitrous oxide, the day after. She exhibited the same phænomena, and died in it in about five minutes and half. _d._ A small dog that had accidentally met with a dislocation of the vertebræ of the loins, and was in great pain, as manifested by his moaning and whining, was introduced into a large jar of nitrous oxide. He immediately became quiet, and lay on his side in the jar, breathing very deeply. In four minutes his respiration became noisy, and his eyes sparkled very much. I was not able to apply my hand to the thorax. In five minutes he appeared senseless, and in seven minutes was perfectly dead. _e._ A strong rabbit, of ten or twelve months old, was introduced into nitrous oxide. He immediately began to struggle very much, and in a minute fell down senseless: in two minutes the legs became convulsed, and his inspirations were deep and noisy: in less than five minutes he appeared perfectly dead.