Section 24. No death benefit certificate as to any child shall be issued unless the society shall simultaneously put in force at least 500 such certificates, on each of which at least one assessment has been paid, and so long as the number of lives presented by such certificates does not fall below 500. A society that has so put in force at least 500 certificates on each of which at least one assessment has been paid may, during the year after first putting in force said number of certificates, continue to issue certificates notwithstanding withdrawals reducing the number of certificates in force to less than 500, if the number of such certificates does not remain below 500 for a period exceeding 90 days. The death benefit contributions to be made upon such certificate shall be based upon the Standard Industrial Mortality Table or the English Life Table Number Six, with a rate of interest not greater than 4 per cent per annum, or upon a higher standard. Contributions may be waived or returns may be made from any surplus held in excess of reserve and other liabilities, as provided in the by-laws, but extra contributions shall be made if the reserves provided for in the following section become impaired. Such society may grant to the holder of such a certificate extended or paid-up protection or such withdrawal equities as its constitution and by-laws may provide, but in no case to exceed in value the reserve held against the individual certificate.