While there are such pitfalls for the historian in identifying the several species of fevers in former times, there are other difficulties of interpretation which concern the varieties of a continued fever, or its changes of type from generation to generation. Is change of type a reality or a fiction? And, if a reality, did it depend at all upon the use or abuse of a certain regimen or treatment, such as blooding and lowering, or heating and corroborating? A pupil of Cullen, who wrote his thesis in 1782 upon the interesting topic of the change in fevers since the time of Sydenham[3], inferred that the great physician of the Restoration could not have had to treat the low, putrid or nervous fevers of the middle and latter part of the 18th century, otherwise he would not have resorted so regularly to blood-letting, a practice which was out of vogue in continued fevers at the time when the thesis was written, as well as for a good many years before and after. Fevers, it was argued, had undergone a radical change since the time of Sydenham, in correspondence with many changes in diet, beverages and creature comforts, such as the greatly increased use of tea, coffee and tobacco, and of potatoes or other vegetables in the diet, changes also in the proportion of urban to rural population, in the use of carriages, and in many other things incident to the progressive softening of manners. In due time the low, putrid, nervous type of typhus fever, which is so much in evidence in the second half of the 18th century, ceased to be recorded, an inflammatory type, or a fever of strong reaction, taking its place; so that Bateman, of London, writing in 1818, said: “The putrid pestilential fevers of the preceding age have been succeeded by the milder forms of infectious fever which we now witness”; while Armstrong, Clutterbuck, and others, who had revived the practice of blood-letting in fevers shortly before the epidemic of 1817-18, claimed the comparatively slight fatality and short duration of the common fever of the time as an effect of the treatment. After 1831, typhus again became low, depressed, spotted, not admitting of the lancet; on which occasion the doctrine of “change of type” was debated in the form that the older generation of practitioners still remember.