Strictly analogous to this, in its principle of choice and in its method of operation, appears the epidemic action--not on persons indeed, but on places. The specific migrating power--whatever its nature, has the faculty of infecting districts in a manner detrimental to life, only when their atmosphere is fraught with certain products susceptible, under its influence, of undergoing poisonous transformation. These products, it is true, are but imperfectly known to us. Under the vague name of putrefaction we include all those thousand-fold possibilities of new combination, to which organic matters are exposed in their gradual declension from life. The birth of one such combination rather than another is the postulate for an epidemic poison. Whether the ferment, which induces this particular change in certain elements of our atmosphere, may ever be some accident of local origin, or must always be the creeping infection from similar atmospheres elsewhere similarly affected; whether the first impulse, here or there, be given by this agency or by that--by heat, by magnetism, by planets or meteors--such questions are widely irrelevant to the purpose for which I have the honour of addressing you. The one great pathological fact, which I have sought to bring into prominence for your knowledge and application, is this:--that the epidemic prevalence of Cholera does not arise in some new cloud of venom, floating above reach and control, high over successive lands, and raining down upon them without difference its prepared distillation of death; but that--so far as scientific analysis can decide, it depends on one occasional phase of an influence which is always about us--on one change of materials which in their other changes give rise to other ills; that these materials, so perilously prone to explode into one or other breath of epidemic pestilence, are the dense exhalations of animal uncleanness which infect, in varying proportion, the entire area of our metropolis; and that, from the nature of the case, it must remain optional with those who witness the dreadful infliction, whether they will indolently acquiesce in their continued and increasing liabilities to a degrading calamity, or will employ the requisite skill, science, and energy, to remove from before their thresholds these filthy sources of misfortune. * * * * * 2. If, gentlemen, I have detained you long in stating conclusions as to the habits of the disease, and as to the significance of its local partialities, it has been in order to render quite obvious to you the intention of those precautionary measures which it is now my duty to recommend. First, I would allude to influences of an exterior and public kind; and here, all that I have to advocate might be included in a single stipulation, that cleanliness--in the widest sense of the word--should be enforced to the full extent of your authority.