Section 13. Expenses

All  officers,  clerks,  inspectors,  experts  and
  employees of the commission shall receive the compensation fixed by  the
  chairman  of  the commission within the amounts appropriated therefor by
  the legislature. The commissioners and counsel  to  the  commission  may
  receive,  in  lieu  of  expenses,  twenty-five  dollars  per  day, and a
  proportionate amount thereof for each fraction of a day,  while  engaged
  in  the performance of official duties at a place other than the city to
  which they are regularly assigned,  and  shall  be  reimbursed  for  the
  actual  and  necessary  cost  of  transportation  incurred by them; this
  provision, however, shall  not  be  applicable  to  the  chairman  or  a
  commissioner receiving a definite sum in lieu of traveling expenses. The
  officers,   clerks,   inspectors,  experts  and  employees,  shall  have
  reimbursed to them all actual and necessary traveling and other expenses
  and disbursements incurred or made by them in  the  discharge  of  their
  official duties.