Members of such association shall be required to pay yearly in advance cash premiums and in addition thereto an amount in negotiable notes or cash sufficient to maintain a reserve equal to that required of other companies doing the same class of business. Notes shall be payable in whole or in part on the vote of the directors of the association as such payments may be required to meet estimated losses or expenses in excess of the current cost and to meet claims covering losses not payable within the same fiscal year within which the claim originated. The directors may fix rates of interest on either notes or balances.