Any teacher who has been credited under the rules and regulations of such board of education with an aggregate of twenty-five or more years of teaching experience may be retired by such board of education on account of disability or incapacity, physical or otherwise. Any teacher so retired, provided that at least fifteen years of such accredited teaching experience shall have been in the public schools of said cities, shall be entitled to receive from such retirement fund, during the period of retirement, monthly installments, the annual aggregate of which shall be such percentage of five hundred dollars as the number of years of such accredited teaching experience of the beneficiary shall bear to the term of thirty years. Any teacher so retired may, at the discretion of the board of education, should such teacher’s incapacity or disability be removed, be reinstated as a teacher, and any right to any payments from this fund until such teacher again be retired shall cease with such reinstatement. And shall any teacher be so reinstated, the years of such retirement shall be included in arriving at the term of service when such teacher may again be retired, but no credit for such years of retirement shall be given in arriving at the amount such teacher shall be entitled to receive from the retirement fund.