distinctively medical character. As the two first chapters are pervaded by social and economic history, so each of the others will be found to have one or more points of distinctive interest besides the strictly professional. Smallpox is perhaps the most suitable of all the subjects in this volume to be exhibited in a continuous view, from the epidemics of it in London in the first Stuart reigns to the statistics of last year. While it shares with Plague the merit, from a historical point of view, of being always the same definite item in the bills of mortality, it can be shown to have experienced, in the course of two centuries and a half, changes in its incidence upon the classes in the community, upon the several age-periods and upon town and country, as well as a very marked change relatively to measles and scarlatina among the infective scourges of infancy and childhood. For certain reasons Smallpox has been the most favoured infectious disease, having claimed an altogether disproportionate share of interest at one time with Inoculation, at another time with Vaccination. The history of the former practice, which is the precedent for, or source of, a whole new ambitious scheme of prophylaxis in the infectious diseases of men and brutes, has been given minutely. The latter practice, which is a radical innovation inasmuch as it affects to prevent one disease by the inoculation of another, has been assigned as much space in the chapter on Smallpox as it seems to me to deserve. Measles and Whooping-cough are historically interesting, in that they seem to have become relatively more prominent among the infantile causes of death in proportion as the public health has improved. Whooping-cough is now left to head the list of its class by the shrinkage of the others. It is in the statistics of Measles and Whooping-cough that the principle of population comes most into view. The scientific interest of Scarlatina and Diphtheria is mainly that of new, or at least very intermittent, species. Towards the middle of the 18th century there emerges an epidemic sickness new to that age, in which were probably contained the two modern types of Scarlet Fever and Diphtheria more or less clearly differentiated. The subsequent history of each has been remarkable: for a whole generation Scarlatina could prove itself a mild infection causing relatively few deaths, to become in the generation next following the greatest scourge of childhood; for two whole generations Diphtheria had disappeared from the observation of all but a few medical men, to emerge suddenly in its modern form about the years 1856-59.