The opinion may be entertained, that the effluvia of sick rooms may fasten to the furniture, &c., and in that situation, even where ventilation is maintained, form centres from whence they may be disengaged, either constantly, for a long period, or only on occasions which are particularly favourable for their redissemination in the atmosphere. It is common to designate these effluvia primarily disseminated in the atmosphere, and the vitiated air which is formed in old fever and plague wards, and to which reference has just been made, Contagion, without any other term to mark the distinction between these principles and those which are legitimately so called. In a previous part of this work, the distinction has been carefully made, and it was shewn that the effluvia under discussion do not form, strictly speaking, a contagious, but only a vitiated atmosphere. As it appears that effluvia which arise from the bodies, and the excretions of the sick, do not only mingle with the atmosphere, but also adhere to furniture, walls, &c., when concentrated and long exhaled, it becomes necessary not only to remove that atmosphere in which they are disseminated, but also to adopt means for the purification of all those bodies to which they may adhere, in order that the atmosphere may not become again and again loaded with them, arising, as they may, from the places to which they are adhering. The means best calculated to obtain that end, are those processes to which reference was made above, viz. rubbing, scouring, washing, and exposing to the free action of the air. But besides these means of purification, there are others, as fumigations, which are calculated to be highly useful, and which should be used on all occasions of severe general disease. Fumigations are vapours of an elastic nature, permanent and non-permanent. They are diffused through the atmosphere, and impart to it their peculiar odours. They are highly useful. In the _first_ place, there is reason to believe that they, especially the more active, may decompose the effluvia which are mingled with the atmosphere, and which are adhering to solid bodies, all of which they can be made to reach and act upon, and even to penetrate where the scrubbing-brush and hot water cannot be applied; in the _second_ place, they insure a change of atmosphere; and, in the _third_ place, they effectually cover or hide the smell of the sick-room, which is at all times highly disagreeable, and which is often regarded with great terror and apprehension, being ever associated with ideas of contagion and disease;—and in this way, fumigations are found of very great value, giving, at the same time confidence to the timid, and affording something different from what contagion is commonly thought to be, on which the organ of smell may be safely exercised.