Section 6. No action for the recovery of damages for injury under section one of this chapter or for death under section two B or six C of chapter two hundred and twenty-nine shall be maintained unless notice of the time, place and cause of the injury is given to the employer within sixty days, and the action is commenced within two years, after the accident which causes the injury or death. Such notice shall be in writing, signed by the person injured or by a person in his behalf. If the person injured dies within the time required for giving the notice, his executor or administrator may give such notice within sixty days after his appointment; and in such case the action may be begun within one year after the appointment of such executor or administrator. If from physical or mental incapacity it is impossible for the person injured to give the notice within the time provided in this section, he may give it within ten days after such incapacity has been removed, and if he dies within said ten days his executor or administrator may give such notice within sixty days after his appointment. If the employer dies without such notice having been given and before the time for giving such notice has elapsed, the notice may be given to his executor or administrator, and the time within which the notice may be given as herein provided shall run from the appointment of the executor or administrator. A notice given under this section shall not be held invalid or insufficient solely by reason of an inaccuracy in stating the time, place or cause of the injury if it is shown that there was no intention to mislead, and that the employer was not in fact misled thereby. If the employer dies without such action having been brought and before the time for bringing the action has elapsed, the action may be begun against his executor or administrator not less than six months and not more than one year after the executor or administrator has given bond for the performance of his trust. Any form of written communication signed by the person so injured, or by some person in his behalf, or by his executor or administrator, or by some person in behalf of such executor or administrator, containing the information that the person was so injured, giving the time, place and cause of the injury or death, shall be considered a sufficient notice. Want of notice as required by this section shall not bar proceedings if it is shown that the employer, or any agent of the employer exercising superintendence, had knowledge of the injury, or if it is found as a fact that the employer was not prejudiced by such want of notice.