Sec. 4. PER CAPITA CONTRIBUTIONS. Commencing with the next calendar month, immediately following the effective date of this Act, per capita contributions of all such members of each such police department as participate in such fund, as aforesaid, shall be made to said fund. Said monthly per capita contribution shall be made as follows: The salary and future salary of each member participating in such fund is hereby reduced Three Dollars ($3) per month, but said Three Dollars ($3) per month shall be paid by such city into the said pension fund. No other money paid into said pension fund, however, shall be counted as a part of salary, under any law or ordinance fixing or pertaining to salaries of members, of any such police department.