Section 172. Money received by a county treasurer under the preceding sections relating to dogs, and not paid out for damages, license blanks or books, record books, anti-rabic vaccine or other purposes as required under said sections, shall, in January, be paid back to the treasurers of the towns in proportion to the amounts received from such towns, and the money so refunded shall be expended for the support of public libraries or schools. In Suffolk county, money so received by the town treasurer and not so paid out shall be expended by the school committee for the support of public schools.