From the fact of the plague prevailing principally among the poor, and rarely attacking the rich, it may be inferred either that the plague is produced ex clusively by the filth, crowding, and bad food to which the poor are subject ; or that if it be contagions, the contagion does not in general take effect upon the in habitants of spacious and well venti lated houses, who are clean in their persons, orderly in their habits, and have a sufficient supply of wholesome food. We see that diseases which ap pear to be contagious under nearly all circumstances, prevail equally among the rich and poor ; and that none of the physical advantages possessed by the latter afford any security against it. Thus, before the introduction of vaccina tion, small-pox was equally destructive to persons of all ranks in society ; and the contagious diseases which attack chil dren, as measles and hooping-cough, make no distinction between the chil dren of the rich and the poor.
There seems to us to he no reasonable doubt that the plague is contagious—in other words, that it can be communicated directly from one person to another—pro vided there be circumstances favourable to its transmission. A quarantine for persons may therefore be expedient for countries where the spread of the plague, supposing it to be introduced, is not im probable. The duration of this quaran tine ought to depend upon the time during which the disease may be latent in a person who has taken it by conta gion 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 to the protomedico of Malta respecting the plague in Malta of 1813, state that "the periods at which the disease made its appearance in differ ent individuals after communication were various. It was generally from the third to the sixth day ; sometimes longer, even to the fourteenth day. but not latter." (Dr. Maclean, On Epidemic and Pestilential Diseases, vol. ii. p. 29.) M. Squr Dupeyron, the secretary of the Council of Health in France, states, in in his Report on Quarantine to the Minis ter 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 introduced into the lazarettoes confirm this opinion" (p. 48). We believe that the cases of
plague which have of late years occurred is the lazarettoes of Valletta, Marseille, and Leghorn have broken out either al sea or shortly after the ship's arrival. When the line of French steamers was first established, in 1837, between Mar seille and the Levant, it was arranged that the steamers coming from the Levant should perform their quarantine at Marseille. But in consequence el several cases of plague having broken out on board the steamers before they could reach Marseille, the French go vernment decided that they should per form 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 Sur 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 immediately after their visit" (p. 76). We believe the idea that actual contact is necessary for the communication of the plague to be utterly erroneous ; and we entertain no doubt that under circum stances 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 physi cians, guardians, and others, who come within a short distance of the plague patients in lazarettoes, by the supposition, that with the isolation, cleanliness, and good ventilation of a well-managed laza retto, the contagion of the plague is ex ceedingly feeble.
With respect to the quarantine of animals, it may be remarked that, ac cording to the belief commonly received in 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 com municated by other animals, especially by cats. (See Maclean, vol, i. p. 202.) We suspect that there is no foundati‘m for the notion that plague can be com municated by means of animals.