The object of quarantine is to prevent the introduction of epidemic diseases from one country into another, and the agency which it employs for this purpose is the isolation of the sick; the detention of, and the placing under inspection for a given period, persons who come from an infected country or district, though they may not be actually sick; and the purification of articles of commerce presumed to be capable of imbibing and conveying pestilential virus, before such articles are landed and dispersed. It appears that facts and observations place beyond all reasonable doubt the utter inutility of this system. If there be any truth in the preceding representation, that epidemic diseases are universally and inseparably connected with an epidemic atmosphere, the question is at once decided. Quarantine can exercise no more control over this epidemic atmosphere than over the electricity and temperature of the common atmosphere, and the direction and force of the wind. If it be true that epidemic diseases, such, for example, as influenza and cholera, traverse the globe in determinate courses or zones, and often spread from country to country, and through the vast populations of their great cities, in single weeks, and even days, it must be futile to array such a machinery as that of quarantine, that is to say, a vessel placed at the entrance of one or two seaport towns, a line of soldiers guarding a few miles of the frontier, of a particular country against morbific agents, which pursue their course like the blight that destroys the vegetation of a country in a night, and which extend their influence over the greater part of the habitable globe. If it be true that the epidemic influence precedes the actual outbreak of epidemic disease—that that epidemic influence is present in a country, creating a predisposition or susceptibility to disease before the epidemic appears in its true and recognized form,—quarantine must be futile, because, before it takes its precautions or erects its barriers, such as they are, the epidemic is already in the country busy in action, vitiating the blood of the most susceptible of the population, and preparing the way for its general attack. If it be true, as ancient and modern authorities are agreed, that, without the essential preliminary of an epidemic atmosphere on the spot, foreign contagion is inert, and that, unless both concur, no pestilence ensues, quarantine under any circumstances must be useless; for in the absence of an epidemic atmosphere it must be useless, because then no disease will spread beyond the individual affected; and with the presence of an epidemic atmosphere it must be useless, because then the disease will spread wherever the infected atmosphere goes and finds favouring conditions.