Section 53. The school committee shall appoint one or more school physicians and registered nurses, shall assign them to the public schools within its jurisdiction, shall provide them with all proper facilities for the performance of their duties and shall assign one or more physicians to the examination of children who apply for health certificates required by section eighty-seven of chapter one hundred and forty-nine, but in cities where the medical inspection hereinafter prescribed is substantially provided by the board of health, said board shall appoint and assign the school physicians and registered nurses. The department may exempt towns having a valuation of less than one million dollars from so much of this section as relates to school nurses.