Appearance of Plague in Porto Rico, New Orleans and Manila.—The developments of 1912, which most concern us, were the appearance of human plague and the discovery of plague-infected rats in Porto Rico, Cuba, and the Philippines, and the discovery of infected rats in New Orleans. Thus the Atlantic cities of the United States were for the first time seriously threatened, and the menace of the pestilence at home loomed up on our horizon with sufficient prominence to excite public concern. Our protectors and guardians of the United States Public Health Service, to whose watchfulness we must credit our prolonged escape from the plague, are carrying out all the protective measures at their command with the utmost activity.
At the present time we find Porto Rico freed from the disease. New Orleans has undergone and is still undergoing treatment which may be expected, most confidently, to clear it of both human and animal plague.
Of Manila and the work there, much will be found in the following pages, but as both rat plague and human plague have been absent for more than a year we may fairly look upon the epidemic as ended. After so long an interval as this any reappearance of plague may fairly be viewed as a new epidemic, although it is not humanly possible to say that rat plague has entirely and permanently disappeared from the city of Manila, as yet.
[CHAPTER II
THE CAUSE AND THE MENACE OF PLAGUE]
The foregoing facts are quite sufficient to make us realize both the possibility and the danger of a world-epidemic; a danger which has existed for some years and which recently has been especially menacing to the United States.
Causation of the Disease.—Plague is an acute infectious epizoötic disease, caused solely by Bacillus pestis, a bacterial organism. The disease is common to man and to a number of the lower animals and fowls.
Prominent among the animals susceptible to the disease is the rat, and from this animal, through the intermediation of the flea, by far the most cases of human plague arise. In California the ground squirrel (Citellus beecheyi), a rodent closely related to the marmots of Asia, plays a similar rôle. Of the Asian marmots, the tarbagan, a large rodent, also commonly suffers from subacute chronic plague, which is transmissible to man as an acute disease by the fleas which the animal harbors.
Its Conveyance.—Although conveyance of plague through rats by contact alone—that is to say without the medium of the flea—is denied by modern experimenters, it is perhaps wiser and safer to consider the disease infectious, inoculable and contagious in the common medical meaning of these terms. While it is usually conveyed to man by the flea, it may be acquired by the inhalation of plague bacilli and, according to some authorities, by ingesting or swallowing the bacilli.