During a most severe and mortal visitation of that disease in Tranent and its surrounding country, which lasted from about the end of January to the 20th October 1836, many cases occurred, where brothers and sisters of children suffering under that malady, living in the same apartment, but not sleeping together, remained free of any attack whatever at the time. Had the poison been capable of diffusion in the atmosphere, the air would have become highly contagious, and as persons were constantly inhaling it, and among them some liable to the disease, it would certainly have manifested its peculiar pestiferous influence upon them. But the result was different, and the person exposed at that time remained quite free of it; and in the course of time, varying from weeks to several months after, went through the disease in the ordinary manner. These cases have been carefully noted and preserved. But the Author was anxious to ascertain, by other means, whether that disease was capable of propagation by atmospheric contagion; and opportunities were not wanting. It occurred that the matter of ulcers, in the throat, might possibly contain the contagious poison, and might be made the subject of experiment. The following is a case in which the experiment was made. The patient, a boy eight years old, had been exposed about three months before, constantly, to an atmosphere in which a younger brother, ill of scarlet fever, was breathing. He had the precursory fever, and the tonsils and uvula (the parts at the back of the mouth) were almost covered with ash-coloured spots and suppurating ulcers. A piece of linen, fixed to the extremity of a probe, was rubbed freely over the ulcers. The linen impregnated with matter and the secretions, was, within an hour or two of its being taken, exposed to the free action of the air of a small apartment, where it remained for ten days, without producing any effect, upon several persons, a good deal in the room; and among them, two children, one aged two, and the other fourteen years, who had not had scarlet fever. They respired the air occasionally and for a considerable time, on the several days. The temperature was various. During the day being about 60° Fahr., and 40° during the night. The linen readily became dry, but was repeatedly moistened with water. This experiment goes to shew, that the matter of the ulcers of scarlet fever is incapable of propagating the disease, through the medium of the air. But scarcely any better nidus could be formed, for the dissemination of the matter, of the ulcers, through the atmosphere, than the sores themselves, the very place where it is eliminated; and cases have been referred to, where persons have respired an atmosphere thus liable to be acted on, with the most complete impunity. It is not ascertained that the contagious poison is eliminated at the sores in the throat, but such seems probable, seeing that the sores are as essential and constant as the eruption itself.