ยง 8401. Computation by clerk. Costs, disbursements and additional allowances shall be taxed by the clerk upon the application of the party entitled thereto. A valuation of property necessary for fixing an additional allowance shall be ascertained by the court, unless it has been fixed by the decision of the court, verdict of the jury, or report of the referee or commissioners, upon which the judgment is entered. The clerk, whether or not objection is made, shall examine the bills presented to him for taxation; shall satisfy himself that all the items allowed by him are correct and allowable; and shall strike out all items of disbursements, other than the prospective charges expressly allowed by law, not supported by affidavit showing that they have been necessarily incurred and are reasonable in amount. The clerk shall insert in the judgment the total of the amount taxed as costs, disbursements and additional allowances.