The contributions of contributors shall, subject to section 35A, be deducted from their salaries at each payment of salaries, and shall be paid, without deduction for postage, forwarding, or exchange, to the Board:
Provided that where a contributor is on leave of absence through illness, either without pay or at less than full pay, the Board may, upon his application, permit the contributions falling due during his absence to be paid by him in such smaller sums, and at such periods, as the Board approves.