Thus the task of the historian, whose first duty is to ascertain, if he can, the actual matters of fact, or the realities, in their sequence or chronological order, is made especially difficult, in the chapter on continued fevers, by the contemporary influence of theoretical pathology or “a preconceived fancy,” by the ascription of modifying effects to treatment, whether cooling or heating, lowering or supporting, and, most of all, by the absence of that more exact method which distinguishes the records of fever in our own time. Nor can it be said that the work of historical research has been made easier in all respects, by the exact discrimination and perfected diagnosis to which we are accustomed in present-day fevers. In the years between 1840 and 1850, the three grand types of fever then existing in Britain, namely, spotted typhus, enteric, and relapsing fever, were at length so clearly distinguished, defined and described that no one remained in doubt or confusion. Thereupon arose the presumption that these had always been the forms of continued fever in Britain, and that the same fevers, presumably in the same relative proportions to each other, might have been left on record by the physicians of former generations, if they had used the modern exactness and minuteness in observing both clinical history and anatomical state, which were seen at their best in Sir William Jenner. It would simplify history, indeed it would make history superfluous, if that were really the case. There are many reasons for believing that it was not the case. As Sydenham looked forward to his successors having experiences that he never had, so we may credit Sydenham with having really seen things which we never see, not even those of us who saw the last epidemics of relapsing fever and typhus. It is due to him, and to his contemporaries and nearest successors, to reciprocate the spirit in which he concludes the general chapter on epidemics prefatory to his annual constitutions from 1661 to 1676: “I am far from taking upon myself the credit of exhausting my subject in the present observations. It is highly probable that I may fail even in the full enumeration of the epidemics. Still less do I warrant that the diseases which during the years in question have succeeded each other in the sequence about to be exhibited shall remain the same in all future years. One thing most especially do I aim at. It is my wish to state how things have gone lately; how they have been in this country, and how they have been in this the city which we live in. The observations of some years form my ground-work. It is thus that I would add my mite, such as it is, towards the foundation of a work that, in my humble judgment, shall be beneficial to the human race. Posterity will complete it, since to them it shall be given to take the full view of the whole cycle of epidemics in their mutual sequences for years yet to come[4].”