The sources of the work have been the ordinary first-hand sources of English history in general. In the medieval period these include the monastic histories, chronicles, lives, or the like (partly in the editions of Gale, Savile, Twysden, and Hearne, and of the English Historical Society, but chiefly in the great series edited for the Master of the Rolls), the older printed collections of State documents, and, for the Black Death, the recently published researches upon the rolls of manor courts and upon other records. From near the beginning of the Tudor period, the Calendars of State Papers (Domestic, Foreign, and Colonial), become an invaluable source of information for the epidemiologist just as for other historians. Also the Reports of the Historical Manuscripts Commission, together with its Calendars of private collections of papers, have yielded a good many facts. Many exact data, relating more particularly to local outbreaks of plague, have been found in the county, borough, and parish histories, which are of very unequal value for the purpose and are often sadly to seek in the matter of an index. The miscellaneous sources drawn upon have been very numerous, perhaps more numerous, from the nature of the subject, than in most other branches of history. Medical books proper are hardly available for a history of English epidemics until the Elizabethan period, and they do not begin to be really important for the purpose until shortly before the date at which the present history ends. These have been carefully sought for, most of the known books having been met with and examined closely for illustrative facts. In the latter part of the seventeenth century the best English writers on medicine occupied themselves largely with the epidemics of their own time, and the British school of epidemiology, which took a distinguished start with Willis, Sydenham and Morton, was worthily continued by many writers throughout the eighteenth century; so that the history subsequent to the period here treated of becomes more and more dependent upon medical sources, and of more special interest to the profession itself. Reference has been made not unfrequently to manuscripts; of which the more important that have been used (for the first time) are a treatise on the Sweating Sickness of 1485 by a contemporary physician in London, two original London plague-bills of the reign of Henry VIII., and a valuable set of tables of the weekly burials and christenings in London for five years (almost complete) from 1578 to 1583, among the Cecil papers--these last by kind permission of the Marquis of Salisbury.