The plague, in its various visitations, from the time of its prevalence in Athens, as described by Thucydides and Lucretius, down to the period when it last raged in England, viz. in the year 1665, has been observed to be coincident, for the most part, with circumstances proving the existence of vitiated air: and at this day the most mortal diseases prevail, where foul air exists, whether that arises from this or that source. The atmosphere becomes vitiated, when great numbers of men in health are crowded together in apartments too close and confined to admit of a sufficient supply of pure air for the perfect maintenance of respiration. In this case, the vitiation is effected by the abstraction of the oxygen of the atmosphere, the exhalation of carbonic acid gas, and the dissemination of effluvia which arise from the bodies of those who are confined. The immediate effects of confinement to an atmosphere thus vitiated are, oppressed breathing, sense of great anxiety and suffering, fixedness of the eyes, and torpor, which gradually increases to insensibility; and the miserable sufferer dies bereft of sense and motion, from suffocation. When the atmosphere is not so impure as to cause immediate death, disease of a putrid character, for the most part takes place. Typhus fever attacked those persons who survived the memorable struggle in the black hole of Calcutta. A low form of fever used to commit great havoc in jails and other places of confinement, where prisoners were wont to be crowded together in great numbers, from the atmosphere being deprived of its more vital part, and being loaded with unwholesome emanations arising from the filthy persons, and clothes of those confined. This disease is called “Jail Fever,” and manifests a peculiarly malignant character. In hospitals crowded with wounded soldiers, but otherwise in health, where sufficient ventilation cannot be maintained, the same distemper makes its appearance, and is there denominated “Hospital Fever.” In besieged towns and in camps, where the inmates are exposed to the offensive and unwholesome effluvia, commonly experienced in such situations, the same putrid disease prevails, and goes under the name of “Camp Fever.” AIR VITIATED WITH EFFLUVIA FROM BODIES IN A STATE OF DISEASE. Air vitiated with effluvia from bodies in a state of disease, and their excretions, has been variously denominated. By some it has been styled “Contagious Air;” by some “Infectious Air;” and, when it is in connection with fever, “Febrile Miasm or Contagion.” Vitiated air of this kind differs from that referred to above, in this particular, that it arises from bodies in a state of disease. Both forms of vitiated air produce, or assist to produce, disease of the same character; but as the latter form not only goes to produce disease, but arises from disease also, it has been considered to be analogous to the contagious poisons, such as those of small-pox, cow-pox, and the like.