The treasurer of the county in which the board has its principal place of business and operates, shall act as treasurer of the board ex officio, and he shall receive such compensation for such services as may be fixed from time to time by the board. He shall be liable on his official bond for the safekeeping of board funds, and his bond shall be increased or diminished from time to time as the condition, amount and safety of the funds of the board in his hands may require.