In the successive stages of a typical case of variola a marked change in the character of the treatment is demanded both by the peculiarities of the eruption and the accompanying general symptoms. Instead of considering the various types of variola from a therapeutic stand-point, therefore, it would seem more practical to discuss in their natural order those measures which are adapted to the successive stages of the disease, beginning with the *Period of Incubation.*--During this period, which extends from the date of infection to the appearance of the earliest symptoms of the disease, treatment is rarely demanded, since in the great majority of cases the outbreak of the disease is a surprise, and in no case can it be positively known that a patient has smallpox until the initial symptoms appear, and often not until the characteristic eruption has developed. In many instances, however, it is quite certain that an individual has been exposed to the contagion of variola; and when such a one happens to be unvaccinated, or has not been vaccinated in recent years, the assumption is strong that the disease may have been contracted and will manifest itself in due time. The question as to whether vaccination can have any notable effect in modifying the course of variola when performed after a person has been exposed to and has contracted the disease is one concerning which a considerable difference of opinion is expressed by modern writers. While some contend that even if vaccination fails to prevent the development of variola it is quite certain to modify its severity, others claim that it can be of no more advantage than locking the barn after a horse has been stolen. The precise effect which vaccination during the stage of incubation may exert upon the subsequent course of the disease is very difficult to determine in one or even a small number of cases, since it is almost impossible to predict in any given case what the severity of the disease will be. In the opinion of Curschmann it is very doubtful whether vaccination can even render the course of smallpox milder. He states that in many instances where vaccination has been performed after exposure to smallpox infection the pustules of vaccinia and variola have been seen developing side by side, the former having apparently no effect upon the latter. In the opinion of Welsh, on the other hand, vaccination after infection often modifies the disease, and not infrequently prevents it altogether. He believes that when vaccinia has advanced to the stage of the formation of an areola around the vesicle, about the eighth day, it begins to exert its prophylactic power against smallpox; and as the period of incubation in variola is usually twelve days or more, an early vaccination may exert its protective influence in advance of the time when the variolous eruption should appear.