I totally disagree with Dr. Macmichael, as I believe most people will, that the notion of _contagion_ in many diseases is "far from being natural and obvious to the mind;" for, since the time that contagious properties have been generally allowed to belong to certain diseases, there has been a strong disposition to consider this as the most natural and obvious mode of explaining the spreading of other diseases. A person sees evidence of the transmission, _mediate_ as well as _immediate_, of small-pox, from one person to another; and, in other diseases, the origin of which may be involved in obscurity, he is greatly prone to assign a similar cause which may seem to reconcile things so satisfactorily to his mind. Indeed there seems, in many parts of the world, a degree of _popularity_ as to quarantine regulations, which is well understood and turned to proper account by the initiated in the mysteries of that department:--for what more common than the expression--"we cannot be too careful in our attempts to _keep out_ such or such a disease?" For my part, I admit that I can more easily comprehend the propagation of certain epidemics by contagion, than I can by any other means, _when unaccompanied by sensible atmospheric changes_; and if I reject contagion in cholera, it is because whatever we have in the shape of fair evidence, is quite conclusive as to the non-existence of any such principle. Indeed abundance of evidence now lies before the public, from various sources, in proof of the saying of Fontenelle being fully applicable to the question of cholera--"When a thing is accounted for in two ways, the truth is usually on the side most opposed to _appearances_." How well mistaken opinions as to contagion in cholera are illustrated in a pamphlet which has just appeared from Dr. Zoubkoff of Moscow! This gentleman, it appears, has been a firm believer in contagion, until the experience afforded him during the prevalence of the disease in that city proved the contrary. He tells us (p. 10), that in the hospital (Yakimanka) he saw "_to his great astonishment_, that all the attendants, all the soldiers, handled the sick, supported their heads while they vomited, placed them in the bath, and buried the dead; always without precaution, and always without being attacked by cholera." He saw that even the breath of cholera patients was inhaled by others with impunity; he saw, that throughout the district of which he had charge, the disease did not spread through the crowded buildings, or in families where some had been attacked, and that exposure to exciting causes _determined_ the attack in many instances. He saw all this, gives the public the benefit of the copious notes which he made of details as to persons, places, &c., and now ridicules the idea of contagion in cholera. Grant to the advocates of contagion in cholera but all the data they require, and they will afterwards prove every disease which can be mentioned to be contagious.