Any person interested in said district or in the issue or sale of said bonds in the issue or sale of refunding bonds or in the making of a contract with the United States or any contract referred to in said petition may demur to or answer said petition. The statutes of this state respecting the demurrer, and the answer to a verified complaint, shall be applicable to a demurrer and answer to said petition. The person so demurring to or answering said petition shall be the defendant to said special proceeding, and the board of directors shall be the plaintiff. Every material statement of the petition not specifically controverted by the answer must, for the purposes of said special proceeding, be taken as true, and each person failing to answer the petition shall be deemed to admit as true all the material statements of the petition. The rules of pleading and practice provided by the statutes of this state, which are not inconsistent with the provisions of this chapter, are applicable to the special proceeding herein provided for. A motion for a new trial must be made upon the minutes of the court. The order granting a new trial must specify the issue to be reexamined on such new trial, and the findings of the court upon the other issues shall not be affected by such order granting a new trial.