At the request of the Governor, or with his sanction, the State Department of Public Welfare shall investigate any state eleemosynary institution against which complaint is made, and the Department of Public Welfare shall have the power to summon any person to appear and produce such books and papers as shall be designated in the summons and to take testimony under oath concerning the matter and institution under investigation. The Department shall have the power to administer oaths to such persons as may be summoned and to enforce such powers as are given to notaries public when they are taking depositions. Evidence of persons restrained in prisons or any other places of detention, if deemed necessary or requested by the witness, shall be taken out of the hearing of persons in authority about such institutions and be preserved and kept secret, and be used only by the Department so far as may be by him deemed necessary to correct or remedy any wrong that is or may be disclosed.