In attempting to lessen the incidence and to reduce the severity of infections of the respiratory tract by vaccination, it is essential to consider the wide range of bacterial flora, the relative prevalence of each species, as well as the fluctuations in incidence and severity of these infections with changes in season. The well-defined tendency of bacteria of the same species to localize differently in different epidemics indicates peculiar infecting and antigenic powers. The short duration of immunity to infections following attacks adds greatly to the difficulty. However, owing to the high incidence and high mortality rate from infections of the respiratory tract during the present epidemic, a painstaking effort to raise the resistance of individuals by inoculation with appropriate vaccines appeared to be strongly indicated.
In considering prophylactic inoculations in this epidemic of influenza, we put aside the debated question as to the cause of the initial symptoms and