permanent habitat in Europe appears to have been a limited area in the southeastern portion, from which it occasionally spread northward, without, however, extending much beyond the limits of the Balkan peninsula. During the early part of the present century it still occurred to some extent in this region, where it prevailed as an epidemic for the last time in 1841.
Typhus fever, like smallpox, is a disease which is transmitted by personal contagion, and its dissemination depends upon human intercourse. It prevails chiefly in temperate or cold regions, and is unknown in the tropics except at considerable elevations above the sea level. In temperate regions its season of greatest prevalence is the winter and spring. There is no reason to suppose that the specific germ, which has not yet been demonstrated, is able to multiply external to the bodies of infected individuals, and, consequently, conditions relating to soil, moisture, temperature, and organic decomposition are apparently without influence in the development of the disease, except in so far as they affect the predisposition of those exposed to infection. Insanitary surroundings no doubt constitute a predisposing cause by lowering the vital resisting power of those exposed to such influences. But of all the predisposing causes war and famine are shown by the history of past epidemics to have been the most potent.
The earliest reliable accounts of epidemics of this disease date from the eleventh century, but it was not until the sixteenth century that well-recorded accounts of the epidemic prevalence of the disease were made, in the first instance by Italian physicians. The disease prevailed extensively in Italy during the years 1505 to 1530. In the seventeenth century numerous fatal epidemics occurred in various parts of Europe, the disease for the most part following in the track of contending armies, and adding to the scourge of war with its devastations and the resulting scarcity of food the disastrous effects of a deadly pestilence. During the eighteenth century the disease continued to prevail in Europe, and three notable epidemics occurred in Ireland: the first in 1708 to 1710, the second from 1718 to 1721, the third from 1728 to 1731. The last two epidemics, although most destructive of life in the famine-stricken districts of Ireland, also extended to a considerable portion of England and Scotland. In 1734 to 1744 typhus prevailed extensively in eastern and central Europe; it again obtained wide prevalence in 1757 to 1775, a period of wars and famine, and during the last ten years of the eighteenth and the early part of the present century, the period of the Napoleonic wars, it again ravaged the countries over which the contesting armies passed. Ireland appears to be one of the endemic foci of this disease, and when it has invaded
