Page:Popular Science Monthly Volume 57.djvu/602

592 judged by its effect, is neither more nor less virulent than its early progenitors. It has often died out in a given locality or country, it has even been forced back to its original ancestral home, but still the same type, the same species has perpetuated itself unchanged. If the plague on its present world-wide journey does not cause such terrible outbreaks as it has in the past, it will be not because the germ has been altered by time, but because man has changed in so far as he has slowly learned and profited by the lessons of previous epidemics.