A case of an apparently strong nature is made out in favour of the propagation of disease by atmospheric contagion, when a person labouring under sickness or lately recovered from it, is removed into a house or locality in which the same malady shortly manifests itself. It is often held conclusive; we hold it otherwise. Such a case is known to take place, and we have observed it in our own practice—but that is not entitled to be considered conclusive. It should be shewn, if that inference is at all to be arrived at, that the occurrence is so frequent that the probability is precluded of attributing the phenomena observed to the ordinary causes of disease, that the number who thus suffer is greatly more in proportion than holds among the population generally, and that, in short, those thus visited by the sick are affected in a greater ratio than holds with the general community, as ascertained by an observation of the whole course of the disease or epidemic. We know that the appearance of disease among those visited by the sick, or those lately recovered, does not always happen. We ourselves, scarcely recovered of typhus fever, have visited and lived with a family at a distance, and no such thing as propagation has occurred—and hundreds of other cases are within our knowledge. We have, after making calculations on the subject, considering both those cases, where disease did occur and where it did not, that, generally speaking, those visited by convalescents, or even patients, suffer in a proportion very little greater, if at all greater, than those having no such intercourse—compared of course with the very many cases that are wont to occur in a widely spread epidemic. Yet, though the general proportion may not be much affected, still we are ready to admit that a case does now and then occur, where disease is shortly observed after the admittance of a sick person in a house or locality, and where the effect is so marked, so immediate and so general among those exposed, that we are compelled to admit that there is room for thinking, that the patient is somehow or other, in some degree at least, the occasion of the catastrophe. It is sometimes observed that servant girls, affected with typhus fever, are in that state sent to their homes, and that disease shortly affects their brothers and sisters, but before such cases can be held as proving the existence of atmospheric contagion, there should be a strong assurance that the agencies of a most unwholesome character, known to exist in such cases, are inert, and that they which have on other occasions, without assistance, produced of themselves the distemper observed, have been altogether impotent and inactive.