Section 36. The surviving spouse, executor or administrator of a registered pharmacist who has died or the spouse of one who has become incapacitated may continue his business under a registered pharmacist, who may also be considered qualified to receive a certificate of fitness under section thirty of chapter one hundred and thirty-eight authorizing him to exercise upon the premises of said deceased or incapacitated pharmacist the rights conferred by section twenty-nine of said chapter upon holders of said certificates; provided, that the registered pharmacist under whom the business is continued is in charge of the premises and present therein.