▁role ▁for ▁two ▁years . ▁In ▁ 1 8 9 8 , ▁Rosen au ▁left , ▁subsequently ▁serving ▁ ▁as ▁the ▁Director ▁of ▁the ▁National ▁H yg ien ics ▁Labor atory , ▁and ▁as ▁a ▁quar antine ▁officer ▁at ▁the ▁Philipp ine ▁Islands ▁and ▁Santiago . ▁In ▁ 1 9 0 1 , ▁he ▁succeeded ▁ ▁Joseph ▁K iny oun ▁as ▁the ▁director ▁of ▁the ▁H yg ien ic ▁Labor atory ▁at ▁the ▁Angel ▁Island . ▁In ▁this ▁role , ▁Rosen au ▁studied ▁the ▁quality ▁of ▁various ▁v acc ines ▁being ▁sold ▁on ▁the ▁market , ▁and ▁found ▁a ▁significant ▁variation ▁in ▁terms ▁of ▁their ▁pur ity . ▁This ▁led ▁him ▁to ▁publish ▁a ▁▁ ▁report ▁that ▁influenced ▁many ▁phys icians ▁and ▁members ▁of ▁the ▁public ▁to ▁call ▁for ▁more ▁government ▁super vision ▁in ▁the ▁manufact uring ▁of ▁v acc ines . ▁ ▁Mil k ▁ ▁Rosen au ▁has ▁been ▁described ▁as ▁a ▁content ious ▁campaign er ▁to ▁make ▁milk ▁safe ▁in ▁the ▁United ▁States . ▁He ▁aim ed ▁to ▁reduce ▁milk bor ne ▁dise ases ▁and ▁stated ▁that ▁" next ▁to ▁water ▁pur ification , ▁paste ur ization ▁is ▁the ▁most ▁important ▁single ▁prevent ive ▁measure ▁in ▁the ▁field ▁of ▁san itation ." ▁ ▁Rosen au ▁author ed ▁The ▁Mil k ▁Question ▁in ▁ 1 9 1 2 ▁which ▁provided ▁arguments ▁support ive ▁of ▁paste ur ization . ▁He ▁public ized ▁research ▁demonstr ating ▁how ▁the ▁rapid ▁he ating ▁of ▁paste ur ization ▁protect s ▁milk ▁from ▁b acter ia ▁cont am