Plague, a term used in the middle ages of all fatal epidemics indiscriminately, but now restricted to a very malignant kind of contagious fever prevailing at certain times and places epidemically, characterised by buboes, or swellings of the lymphatic glands, by carbuncles and petechiæ, and apparently furnishing very imperfect security against its recurrence in the same individual.
The first extensive outbreak of this disease on record took place in the 6th century A.D., and devastated the whole Roman empire. It is supposed to have started from Lower Egypt: but from this time frequent epidemics occurred in Europe, culminating in the Black Death (q.v.) in the 14th century. It continued to ravage the north and west of Europe up till the 17th century. The last outbreak in England in 1663-65 caused the 'Great Plague of London,' and spread almost all over the country (see LONDON, Vol. VI. p. 699). Since the end of the 17th century it has only twice visited western Europe; in 1707-14 it spread from Russia and Hungary as far as Sweden, Denmark, Prussia, and Bavaria; and in 1720-22, being introduced from Syria into Marseilles, it destroyed almost half the population there, and spread through Provence. During all this time its most constant seats, so far as is known, were the countries bordering the Eastern Mediterranean—Lower Egypt, Syria, Asia Minor, and Turkey in Europe. But from all these it has meantime disappeared. The last cases known in Egypt occurred in 1844, and in the others in 1841. It was hoped that the disease had become extinct, but since then it has occurred more than once in Arabia, Tripoli, Persia, and Mesopotamia, and in 1878 it spread to south-east Russia. It has been present in India at least since 1815, sometimes in epidemics (e.g. the 'Páli plague,' 1836-38), but most constantly in districts on the southern slopes of the Himalayas; and it is said to be always found in some parts of China. An outbreak at Hongkong in 1894 was followed by the fearful visitation at Bombay (q.v.) and India in 1896-1901, and reached (in a mild form) even Lisbon and Glasgow in 1900.
It is the most destructive of all known epidemics. Rarely less than 60, sometimes 90 per cent. of those attacked die. 'It often carries off half the population of a town or of a district in which it prevails, and it may completely root out whole families, so that no survivor remains.' The Black Death of 1348-50 is believed to have destroyed not less than a quarter of the population of Europe.
The general symptoms resemble those of other severe fevers: shivering, rise of temperature, aching in head, back, and limbs, sickness, &c. Great weakness succeeds, with mental disturbance leading to coma or delirium. Death often occurs before any characteristic symptoms are developed; but at an early stage dark spots or patches often appear on the skin, produced by subcutaneous hæmorrhages (petechiæ, ecchymoses), and bleeding may also take place from the various mucous membranes. Bleeding from the lungs, though rare in recent epidemics, was regarded as a characteristic symptom of the Black Death in its most virulent form. About the second or third day the most distinctive features of the disease are developed—viz. one or more buboes or glandular swellings, usually in the neck, armpits, or groins: these generally break and lead to prolonged suppuration. In a few cases they are absent altogether. Carbuncles not frequently develop at a later stage of the disease. Good nursing, good nourishment, free stimulation, and early opening of the buboes are helpful. Yersin's inoculation with prepared serum proved useful in the Bombay epidemic of 1896-98. There can be no doubt that it is a highly infectious disease, and that the infection may be conveyed by clothes, bedding, &c., as well as by direct contact with the sick. In all epidemics it has been observed that the unhealthy conditions produced by poverty and filth are extremely favourable to the disease, and that it has been much less prevalent and severe among those in comfortable circumstances and healthy surroundings.
See Hecker's Epidemics of the Middle Ages (published by the Sydenham Society, 1844); Hirsch's Geographical and Historical Pathology (vol. i., New Sydenham Society, 1883); and the articles BLACK DEATH, EPIDEMIC.