two hours to sleep, and when I awoke death, and even firm rigidity, had occurred. I therefore carried out the experiment again on various occasions, and with slight modifications, so as to husband the gas.

Of these experiments, I shall trouble the reader with two only, since they alone conclusively establish the position they were intended to support. In conducting them, as will be seen in the next diagram, a slight difference was introduced; but the principle remained the same.

EXPERIMENT II. Inhalation of Oxygen. I constructed an apparatus consisting of a glass chamber, of smaller dimensions than that used in the preceding experiment. The chamber was capable of holding three hundred cubic inches of gas; it was connected with a large Pepys' gas-holder, charged with oxygen, from which the current passing through it was obtained. By a further arrangement, the current, after leaving the chamber, was made to pass through hydrochloric acid, contained in a potash bulb tube, and was then received into another gasholder, made for a different purpose, as will be described in another place. This third gas-holder secured a reserve fund of oxygen, which had only to be washed freely with lime water, for the removal of carbonic acid, to be rendered fit for retransmission to the first reservoir, and so again through the chamber. The hydrochloric acid was used to absorb any ammonia that might be thrown off into the air of the chamber from the breath or other excretions of the animal.

The subjoined drawing shows the apparatus as in action; the artist, Mr. Aldous, having been present when the experiment was progressing.

The apparatus being ready and the gas-holder

charged with oxygen, made by the decomposition of chlorate of potash, a full-grown healthy guinea pig was placed in the chamber, and a current of the gas

Fig. 4.

A. Gas-holder containing oxygen. B. Chamber containing animal. c. Bulb tube containing hydrochloric acid. D. Reserve gas-holder.

was driven steadily and constantly through the chamber, at the rate of 150 cubic inches per hour. The experiment commenced at half-past one in the afternoon. During the first half-hour the animal breathed with considerable rapidity; then this quickened respiration subsided, and an excited condition followed, the animal frisking about and seeming thirsty, often licking off the moisture on the sides of the chamber. But this condition also subsided; and, after an hour, the creature appeared, for a very long period, to exist in the natural state. For two hours the current of oxygen was kept constantly passing through, a new portion being gene

rated as occasion required. Once or twice in the course of the proceedings, when the oxygen ventilation was for brief intervals suspended, the effects of carbonic acid became markedly symptomatised by difficulty of respiration, lividity of the nose, and restlessness; these symptoms invariably passed off at once when new oxygen was admitted. At the end of eleven hours the animal became exhausted. The exhaustion was quite different from that produced by carbonic acid. There was no insensibility, no spasmodic breathing, no blueness of the feet or nose, but a general feebleness, and constant turning about, with occasional attempts to recline on the side. As soon as these symptoms were fully developed, I stopped the oxygen, and made the animal completely insensible by narcotic vapour. As soon as insensibility was complete, I removed it from the chamber. It was making eight respirations per minute; the heart-beats being irregular, quick, and feeble. I now, with one or two sweeps of the knife, removed the ribs anteriorily, and laid the heart bare; it was seen pulsating quickly. The right auricle was much distended. The cavities were immediately laid open; a watch-glass full of blood, caught from the superior vena cava, coagulated firmly in two minutes, the clot being intensely red. In the right auricle there was a little fluid blood. In the auricula there was a clot of fibrin, distinctly separated, modeled to the part where it was found, and of about the size of a large hemp-seed. The inner surface of the auricle was coated with a fine layer of fibrin, which was easily removable with the point of the scalpel. In the left cavities, fine web-like cords of fibrin were interlaced with the chordæ tendineæ. To the free margins of the aortic valves there were

firmly attached three semi-transparent beads of fibrin, each of the size of a small pin's head. The aortic valves were fringed, on their free margins, with fibrinous. beads, one valve having also a swollen and reddened appearance. In the aorta there lay a thin but long thread of fibrin.

The lungs contained some blood, but were not congested. They were, however, firmer in structure, and less elastic than natural. They floated in water. The vessels of the brain were congested. All the other organs were natural in structure, but unnaturally red in colour.

The operation of laying open the heart extended only over one minute; the organ was opened while yet briskly pulsating; and several attempts at respiration were made by the diaphragm and the chest muscles after the fibrinous deposition had been exposed to view.

EXPERIMENT III. Inhalation of Oxygen. By means of the apparatus described in the last experiment, I subjected a pigeon to the influence of oxygen gas. The experiment commenced at 11 a.m. For six hours after the inhalation but little change was observed in the animal; but at this time, the administration of the gas having been suspended for ten or fifteen minutes while the gasholder was being re-supplied, a severe paroxysm of dyspnoea supervened, but disappeared immediately when a new charge of gas was driven through. At 8 p.m. (nine hours after the commencement of the experiment) the creature became feeble, and each inspiration was attended with a peculiar croupy sound. The respirations were now 28 per minute, and the croupy sound, which was so loud that it could be heard through the walls of the chamber, continued well marked for two

hours. There were the same indications of thirst as were noticed in the guinea-pig. The peculiar noise in the breathing subsided gradually, as a sleep supervened which lasted until half-past eleven, and was remarkably natural. On waking up at the hour named, the creature was less embarrassed in the breathing than it had been before, but it was much exhausted and restless. Its feathers were widely expanded out, and at times it reclined partially on one side. The beak, the eyes, and the feet were intensely red in colour, an appearance which commenced about four hours after the inhalation, and which continued to the end. At 12 o'clock, midnight, (i. e. thirteen hours after the inhalation began) I produced rapid narcotisation. As is usual in birds, the effects of the narcotic were at once developed, and in one minute and a half I removed the animal from the chamber perfectly insensible. The inspirations taken before the body was opened were three in the quarter minute, and deep. The chest was now quickly opened, and the heart laid bare. The muscular action on both sides was rapid. The right auricle, on being opened, was found in great part filled with a firm coagulum, modeled to those parts of the heart-wall against which it had rested. The clot was coloured by red matter. From this coagulum a cord ran downwards into the right ventricle, and, taking the course of the circulation, curved thence upwards for a short distance. But the most remarkable appearance was met with in the left ventricle. Here a firmer coagulum took a bulbous origin at the lower part of the cavity; from this there ran upwards a neck, which, as it approached the auriculo-ventricular valve, divided and ran along the borders of the valve, making a circle or ring from