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.
From the circumstance of this vitiated air arising from persons in disease, and assisting in the propagation of the same malady, it has all along been regarded as a specific contagious animal poison in an atmospheric menstruum; and thus has been created the perplexing and entangled web of confusion and vagueness that has been wove around the principles, viz. contagious poisons, and vitiated air arising from effluvia from persons in disease, and from their excretions.
From this circumstance, these principles, viz. specific contagious poisons, and vitiated air arising from persons in disease, have been erroneously classed together, and a supposed analogy has been created.
But these principles are widely different in their nature, and in the laws by which they are regulated.
The specific contagious poisons produce the same diseases as those with which the bodies, whence they arose, were affected, and them only; and their operation is marked by uniform effects, observing stated and unvarying periods. Vitiated air, of the kind under examination, though it arises from persons in a state of disease, and is sometimes known to operate in the production or propagation of the same distemper, does not always induce disease, does not induce that disease only, whence it sprung, but various others; and, in short, its effects are not uniform, and do not observe stated and unvarying periods.
The specific contagious poisons produce their peculiar diseases, as their proper and only effects, without the cooperation of other influences; but vitiated air, when the same disease extends, whence it arose, cannot be said to be causing its proper, only, and peculiar effects, as the same disease does not invariably follow its action. In general, the effluvia which proceed from a sick person, where they prove hurtful, cause the same distemper as that with which he is affected; for instance, the effluvia arising from a person affected with typhus fever, produce that disease again:—but that is not always the case, and an instance will be presently detailed, where the effluvia which proceeded from a body dead of one disease, produced another of a very different nature.
The reason that the presence of vitiated air is generally attended with the same disease as that with which the body is affected, whence it sprung, is, that there is existing at the time, a disposition to that particular malady: and the vitiated air only gives it form by acting as an ordinary exciting cause upon individuals prepared for its invasion.
It appears probable that vitiated air, unlike the palpable contagious poisons, assists in the production of that disease only which is prevailing, or to which there exists a disposition from the operation of other agencies; and it appears probable that vitiated air, whether it arises from persons affected with this or that disease, will, within certain limits, produce one disease as readily as another, the required particular disposition being present; for instance, that the effluvia from a small-pox patient will induce small-pox or typhus fever, according as there exists a disposition to the one disease or the other, and vice versa.