I have observed the manner in which the breathing and circulation ceased in a great number of instances, with the stethoscope applied to the chest of the animal, when the quantity of chloroform contained in the air it breathed was known, and have notes of the result. The animals were chiefly cats, which would otherwise have been killed by prussic acid, or in some other way. In every instance in which the quantity of vapour in the air breathed by the animals was from three to six per cent., the respiration ceased whilst the sounds of the heart were still very distinct, as in Experiment 23, related above; in many instances the heart continued to beat from two to three minutes after the breathing had ceased, and, in a great number of instances, there were one or more gasping inspirations just at the moment when the sounds of the heart ceased. In many cases these gasping inspirations caused the action of the heart to return, as in Experiment 23, if the animal had been withdrawn from the chloroform; but this was not always the case; and if the chloroform was still breathed during these gasping efforts, all signs of life immediately ceased in every instance. When, on the other hand, the air breathed by the animals contained eight or ten per cent., or upwards, of vapour of chloroform, the action of the heart was always seriously affected and rendered extremely feeble, if it did not actually cease, at the time the breathing was arrested. In several instances, indeed, the sounds of the heart entirely ceased before the breathing, as in Experiment 25; and although the chloroform was withdrawn, in this and many other experiments, the moment the heart ceased to beat, and fresh air was drawn in by inspiratory efforts, it very rarely had the effect of restoring the heart’s action, although this happened so frequently when that organ had gradually ceased to act on account of suspension of the breathing, by the effect of more diluted vapour. In order to see more precisely the action of the vapour of chloroform on the heart, when not sufficiently diluted, the chest and pericardium were opened on four occasions, in cats and a rabbit, and chloroform was exhibited by artificial respiration. I was assisted by Mr. Peter Marshall in these experiments, and the following is the account of one of them.[60]