No dividend shall be declared or paid by any bank until a surplus equal to twenty percent (20%) of the paid-in capital stock of such bank has been built up. Thereafter, the board of directors of any bank may declare a dividend of so much of its net profits as it shall deem expedient; but before any such dividend is declared or paid, not less than one-fifth (1/5) of the net profits of the bank for such period as is covered by the dividend shall be carried to the surplus fund until such surplus fund shall amount to fifty percent (50%) of the paid-in common stock. Any loss sustained by any bank in excess of its undivided profits may be charged to its surplus account, provided that its surplus funds shall thereafter be reimbursed from its earnings in the manner above provided. If such surplus fund is reduced below an amount equal to twenty percent (20%) of the common stock, no further dividend shall be declared or paid until such surplus is restored to that amount, and thereafter dividends shall only be declared and paid in the amount and in the manner above provided until such surplus shall be restored to an amount equal to fifty percent (50%) of the common stock.