The answer to this has been already given.--Let any other cause than contagion or infection be supposed, and the difficulty remains equally great. The probability is in favour of contagion, rather than a general disposition of the atmosphere, because in the latter case the disease would, contrary to experience, begin in a great many places at once; but the plague begins in such a secret manner that we scarce know whence it comes. Like fire, or a ferment in liquors, it diffuses itself far and wide, and lastly, like an immense inundation, the source of which is dried up, it seems to lose its power by extending too far, and dies away altogether. We cannot penetrate into the causes of those things, but, without any speculation at all, we can observe that the disease falls upon people of a certain constitution more than others, and this may be of use in preserving ourselves from it, as shall be explained in the next section. It is still necessary to say something of the infection spreading from one person to another, and being kept off by refraining from communication with the diseased. This indeed naturally follows from its proceeding originally from the cotton: for as all the infected did not touch this cotton, there can be no other cause assigned from its spreading than by communication from one to another; and, therefore, if such communication was cut off, we should naturally think that the disease would not spread. But, in opposition to this, we have already quoted Dr. Moseley giving a long list of convents infected, though they kept themselves strictly shut up. Dr. Russel cites, in favour of prevention by shutting up, two certificates, one by the bishop of Marseilles, the other by the sheriff of the same place. To these he adds the testimony of M. Langeron, who was actively employed throughout the whole time that the plague continued, first as a commodore of the gallies, and afterwards as governor of the town and its dependencies. In opposition to these, however, he takes notice of two passages “in books of acknowledged authority,” which he is at pains to answer; the one is from the Journal already quoted, which says, “and what is unaccountable, those who have shut themselves up most securely in their own houses, and are the most careful to take in nothing without the most exact precautions, are attacked there by the plague, which creeps in no one knows how.” The other passage is taken from the _Relation Historique_, “that, in the height of the pestilence, the infection penetrated into places which had till then remained inaccessible; that monasteries and houses shut up in the most exact manner were no longer places of security.”