Banking corporations which pursuant to the laws of the State in which they are doing business are required to set apart, keep, and maintain in their banks the amount levied and assessed against them by the State authorities as a “Depositors' guaranty fund,” may deduct from their gross income the amount so set apart each year to this fund provided that such fund, when set aside and carried to the credit of the State banking board or duly authorized State officer, ceases to be an asset of the bank and may be withdrawn in whole or in part upon demand by such board or State officer to meet the needs of these officers in reimbursing depositors in insolvent banks, and provided further that no portion of the amount thus set aside and credited is returnable under the laws of the State to the assets of the banking corporation. If, however, such amount is simply set up on the books of the bank as a reserve to meet a contingent liability and remains an asset of the bank, it will not be deductible except as it is actually paid out as required by law and upon demand of the proper State officers.