They, whose hearts are open to the appeal of the forlorn slave, must be gratified to hear that they may perform the offices of humanity to their sick relatives and friends, without, as has hitherto been thought, subjecting themselves to the almost certain invasion of disease; that they may watch the last moments of an expiring friend, minister to his latest wants, and have the melancholy gratification of standing by him, when about to make the last and most awful change that can overtake him. It is expected that it will be shewn, that the sick-room is at all times free of the poison with which it has been believed to be contaminated, and that the atmosphere there, if attention is paid to ventilation, &c. is almost as wholesome as that out of doors. The air which the sick respire does become impure, but not on ordinary occasions in a manner different, or with a greater virulence, than is observed in the case of air in a small and close apartment, respired by many persons closely huddled together. The history of sick chambers presents no instance more dreadful than that of the Black Hole of Calcutta, where so many perished of corrupted or vitiated air. The subject of infectious air touches directly upon the most important interests of mankind, concerns intimately their safety, the duties of man to man, and even the very affections of the heart. As the subject at present stands, the public is awkwardly situated; believing that they must either endanger their health, even their lives, or allow their friends and relatives to perish unassisted. The author thinks he is under no obligation to apologize for attempting to shew, that the public may at once perform all the charities of life to the sick, and avoid the action of a virulent poison. There can be none necessary, and he even hopes that his inquiry may tend to obtain for many, who are yet to be the victims of pestilence, that succour from hands they love, which, alas! has been withheld from thousands. It has not been usual to write speculative medical opinions in a popular style, but the author is of opinion that an inquiry bearing on matters so important, should be made known to those whom it most concerns, certainly, the people; and he is convinced, that in a simple case of evidence such as this, that they are qualified to decide, provided there is a full and impartial leading of facts on both sides, and there be absence of all technical terms and purely professional phrases. The discussion will be conducted on plain and obvious principles, so that the merits of the question may be appreciated, at once, by them and the profession. The public is already informed of much that relates to the animal economy in health, through the assistance of many admirable works which have been published within the last few years, and it is not unfair to suppose that they may be interested in hearing, and likewise capable of understanding, a case relative to disease.