Statistical Data.—The statistics relating to child mortality are in an exceptionally well-developed state, and no unprejudiced student of sociology can afford to ignore them. The literature of child mortality contains a number of extremely important and thoroughly trustworthy works; the reason for this may be that, in comparison with other difficult problems of population, the study of questions of child mortality is easier, because various disturbing influences which complicate adult death-rates have no bearing upon child mortality.