Section 170. Commissioner; deputy

The  commissioner of public welfare may
  appoint one or more deputies, and such  other  subordinates  as  may  be
  prescribed  by  the  board of estimate and apportionment. In case of the
  absence or disability of the commissioner or of a vacancy in the office,
  a deputy shall discharge the duties of the office until the commissioner
  returns,  his  disability  ceases  or  the  vacancy   is   filled.   The
  commissioner, and the deputies before entering upon the discharge of the
  duties of their respective offices, shall each execute and file with the
  city  clerk  an  official  undertaking  in  such  penal  sum  as  may be
  prescribed by the common council.