There seems to us to be no reasonable doubt that the plague is con tagious—in other words, that it can be communicated directly from one person to another—provided there be circumstances favourable to its transmission. A quarantine for men may therefore be expedient for countries where the spread of the plague, supposing it to be, intro duced, is not improbable. The duration of this quarantine ought to depend upon the time during which the diseak may be latent in a person who has taken it by contagion or otherwise.
Since the plague is a peculiarly malignant and destructive fever, and runs its course with a rapidity far greater than typhus, there seems a fair ground for concluding that its poison would not be long latent in the human body. The answers of the protomedico of Malta respecting the plague in Malta of 1313, state that "the periods at which the disease made its appearance in different individuals after communica tion were various. It was generally from the third to the sixth day ; sometimes longer, even to the fourteenth day, but .not later." (Dr. Maclean, On Epidemic and Pestilential Diseases,' vol. ii. p. 29.) M. Segur Dupeyron, the secretary of the Council of Health in France, states, in his Report on Quarantine to the Minister of Commerce (May, 1834), that " the physicians who have made a close study of the plague are pretty generally of opinion that its poison cannot be latent in the human body more than fifteen days ; and the cases of plague intro duced into the lazarettoes confirm this opinion " (p. 48). We believe that the cases of plague which have in recent times occurred in the lazarettoes of Valletta, Marseille, and Leghorn have broken out either at sea or shortly after the ship's arrival. When the line of French steamers was first established, in 1837, between Marseille and the Levant, it was arranged that the steamers coming from the Levant should perform their quarantine at Marseille. But in consequence of several cases of plague having broken out on board the steamers before they could reach Marseille, the French government decided that they should perform their quarantine at the nearest practicable station, namely, Malta.
It is commonly assumed that actual or nearly actual contact is necessary in order to communicate the plague. "All measures against the plague (says M. de S6gur Dupeyron) are founded on the opinion that, except within a very small distance from the body, contact alone can give the disease. Consequently goods taken from ships with different bills of health are often placed in the same warehouse ; and physicians who have visited plague patients, without having touched them, are not put in quarantine, and are permitted to go about imme diately after their visit " (p. 76). We believe the idea that actual con
tact is necessary for the communication of the plague to be utterly erroneous ; and we entertain no doubt that under circumstances favourable to its communication, such as filth, crowding, and want of ventilation, the poison of the plague might be introduced into the human body by inspiration through the lungs. We account for the escape of the physicians, guardians, and others, who come within a short distance of the plague-patients in lazarettoes, by the supposition that in the isolation, cleanliness, and good ventilation of a well-managed lazaretto, the contagion of the plague is exceedingly feeble.
With respect to the quarantine of animals, it may be remarked that, according to the belief commonly received iu the Mediterranean, all living animals are capable of communicating the plague. Accordingly horses, asses, cattle, and sheep are placed in quarantine upon their importation. There is, we believe, an idea among the Franks resident in the plague countries, that the horse cannot communicate the poison of the plague, but that it is frequently communicated by other animals, especially by cats. (See Maclean, vol. i. p. 202) We suspect that there is no foundation for the notion that plague can be communicated by means of animals.
Goods carried in ships or by land are subject to quarantine, accord ing as they belong to the class of susceptible or non-susceptible goods.
Goods which are supposed to be capable of containing and transmitting the poison of the plague are called susceptible. Goods which are sup posed to be incapable of containing and transmitting the poison of the plague are called non-susceptible. All animal substances, such as wool, silk, and leather, and many vegetable substances, such as cotton, linen, and paper, are deemed susceptible. On the other hand, wood, metals, and fruits arc deemed non-susceptible. In Venice an intermediate class, subject to a half quarantine, is introduced between susceptible and non-susceptible goods (Segur Dupeyron, p. 70); but this classifi cation appears to be peculiar to the Austrian dominions. All susceptible goods are unladen lu the lazaretto, and are there exposed to the air, in order to undergo a process of supposed depuration.