Section 85G. Any member of a police or fire department who is hereafter retired under the provisions of sections eighty to eighty-five F, inclusive, and who was appointed a reserve police officer or reserve or call fireman prior to July first, nineteen hundred and thirty-seven, shall, for the purposes of such retirement, be credited with the service actually rendered in any calendar year as such reserve police officer or reserve or call fireman as a part of his continuous service.