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  Established by Edward L. Youmans

              APPLETONS'
           POPULAR SCIENCE
               MONTHLY

              EDITED BY
         WILLIAM JAY YOUMANS

              VOL. LV

        MAY TO OCTOBER, 1899

              NEW YORK
       D. APPLETON AND COMPANY
                1899




          COPYRIGHT, 1899,
     BY D. APPLETON AND COMPANY.




[Illustration: EDUARD OSCAR SCHMIDT.]




APPLETONS' POPULAR SCIENCE MONTHLY.

SEPTEMBER, 1899.




ARE WE IN DANGER FROM THE PLAGUE?

BY VICTOR C. VAUGHAN,

PROFESSOR OF HYGIENE IN THE UNIVERSITY OF M