Mass. Gen. Laws ch. 161 § 115
Any company, except the Boston Elevated Railway Company and the Eastern Massachusetts Street Railway Company, and the successors of either of the said companies, which accepts sections one hundred and fifteen to one hundred and twenty-eight, inclusive, as provided in section one hundred and twenty-six, or has accepted corresponding provisions of earlier laws, shall thereafter furnish service to the public at cost, and shall be subject to said sections, inclusive, with reference to the matters specified therein, but in all other respects shall be subject to the general laws relating to street railway companies. The words "the company" as used in said sections, inclusive, shall mean any street railway company which has accepted said sections or corresponding provisions of earlier laws.
Mass. Gen. Laws ch. 161, § 115