Mass. Gen. Laws ch. 161 § 117
No company may accept sections one hundred and fifteen to one hundred and twenty-eight, inclusive, until it has provided a reserve fund of not less than six, nor more than twelve per cent, of the gross earnings of the preceding year, except as otherwise provided in this section. Such reserve fund may be provided by the issue of either bonds or stock or preferred stock issued under the laws regulating such issues. The reserve fund shall at all times be kept separate and distinct and shall be used only for the purpose of making up a deficiency of income where the income of the company is insufficient to pay the cost of service as provided in the preceding section. Until so used, the reserve fund may be invested in bonds of the United States, or of this commonwealth or any city or town thereof. The reserve fund shall be fully subscribed for upon acceptance of said sections by the company, but shall be paid in, over a period not exceeding two years, at such times and in such amounts as shall be directed by the department. Any company may furnish a larger reserve fund or increase it with the approval of the department. The reserve fund as originally provided for or as later increased shall be considered the normal reserve fund.
Mass. Gen. Laws ch. 161, § 117