The county commissioners in counties of the second class A shall have the power to levy a tax for institution district purposes and for the payment of the obligations of the predecessor poor districts on real estate, trades, occupations and professions, in the same manner and at the same time as county taxes, annual taxes to pay the current expense of the institution district, none of which shall exceed fifteen mills on the dollar of the last adjusted assessed valuation for county purposes: Provided, That no tax shall be levied and collected on trades, occupations and professions at the same time a per capita tax on individuals is levied and collected.
16 P.S. § 4970.1