If any thing could be supposed established by evidence, it is the contagious nature of the plague. It has been traced to the contact of infected persons, and to infected goods ; it is propagated from hand to hand, and preserved dor mant in proper substances for an indefinite length of time; while it is completely prevented by any precautions that are effectual enough to prevent this kind of communica tion. By shutting themselves up in their houses, the Eu ropean consuls and merchants escape it annually in Smyr na, Tripoli, Algiers, and elsewhere ; while the inhabitants, who neglect these precautions, are dying all around them. It has also been propagated by inoculation, as in the case of Dr. White.
It has been argued, on the other hand, against the con tagious nature of the plague, that, if this were the case, its ravages should never cease in those countries like Tur key, where no measures of precaution are taken against it. But this argument applies alike to all contagious dis eases, which exhaust themselves, and are again renewed on favourable occasions, owing to circumstances which we have never vet ascertained. But in truth it never entire ly ceases in Turkey; it slumbers but to break out again, and under favourable circumstances is re-excited, as other contagions are, without 'fresh importation from what we have considered its native scat. Were it not that the mea sures resorted to in Christian countries exterminate it, the case would be the same in these; and that it admits of be ing so exterminated is proof enough of its contagious na ture.
The efficacy of the quarantine laws is an argument of the same kind, since these have always been found effec tual in preventing the importation, except when acciden tally infringed ; and there can be no doubt that all these means, duly enforced, would produce the same effects in all the Turkish states as they have been known to do in Tripoli. Occasional exemptions from the plague form no arguments against its contagious nature, because this hap pens equally in every disease of that kind.
It is next important to remark, that, although the dis order is thus contagious by communication, it is not pro pagated generally through the atmosphere. Were this the case, all the usual precautions would be useless, nor could they have the effects which have been shown to fol.. low them., Thousands of persons in Turkey, daily, and in those cases where it has been imported into Christian countries, have breathed the atmosphere of an infected city, or even of an infected house, without injury. It is a serious mistake to suppose that a single person, or even many infected persons, can contaminate the air of a city.
It is farther an important mistake to imagine, that the propagation of the plague depends entirely on the season, whatever may be the fact respecting Egypt as we formerly stated it. It is proved by much and sad experience, that
neither extremes of heat nor cold have succeeded in check ing its progress in the countries into which it has been im ported, whether in Europe, or Africa, or Asia. The mor tality from this disease has been experienced in every season of the year. In Malta and the Ionian islands, this was sufficiently remarkable, as it has been in other cases of European importation. In Egypt and Turkey, it has, for these last twenty years at least, been found throughout the year at many periods ; and it is not very long since the mortality in Constantinople amounted to 2000 daily, when the streets were covered with snow.
Nevertheless, instances do occur which justify this opi nion to a certain extent. We have already seen what hap pens in Egypt on the occurrence of the north winds in summer. It is also remarkable, that, although a great commerce by caravans is carried on between Palestine, Syria, Arabia, and the East Indies, from' infected places, and that the crews of ships navigating the Persian Gulf have been known to die of the disease ; the plague has very rarely been received at Guzzerat, Surat, or Bombay.
The establishment of these opinions is a matter of the highest importance. It is always when the plague has been mistaken for other diseases, or when its first steps have been overlooked, that its progress has been most se cure, and, ultimately, most fatal. These errors have been frequent and destructive. It is when the disease has ma nifested itself in an unquestionable manner, so as to excite a salutary terror and a conviction of its contagious nature, that it has been counteracted and checked. The great mortality at Marseilles arose from the obstinate disbelief in its contagious nature ; those in London, from its hav ing crept in unperceived till it had spread itself over the whole town, and from the consequent difficulty of adopt ing the necessary regulations. In both, it was at length checked, though late, by the same means as those which we have already described. In these cases it was suffi ciently proved that the air was not infected ; since, in the former city, the Monastery of the Visitation, which was situated between the Plague Hospital and the burying ground, escaped, as did another convent, which lay in the way of that hospital, and past which the sick and suspect ed were carried every day. In Cambridge, the colleges remained uninfected by keeping apart from the town's people ; and, in a plague at Rome, in 1656, the monaste ries were similarly exempt.