§ 4. Assumption of risks; contributory negligence, when a question of fact. An employee by entering upon or continuing in the service of the employer shall be presumed to have assented to the necessary risks of the occupation or employment and no others. The necessary risks of the occupation or employment shall, in all cases arising after the first day of September, nineteen hundred and ten, be considered as including those risks, and those only, inherent in the nature of the business which remain after the employer has exercised due care in providing for the safety of his employees, and has complied with the laws affecting or regulating such business or occupation for the greater safety of such employees. In an action brought to recover damages for personal injuries or for death resulting therefrom received after the first day of September, nineteen hundred and ten, owing to any cause, including open and visible defects, for which the employer would be liable but for the hitherto available defense of assumption of risks by the employee, the fact that the employee continued in the service of the employer in the same place and course of employment after the discovery by such employee, or after he had been informed of the danger of personal injury therefrom, shall not be, as matter of fact or as matter of law, an assumption of the risk of injury therefrom, but an employee, or his legal representative, shall not be entitled under this article to any right of compensation or remedy against the employer in any case where such employee knew of the defect or negligence which caused the injury and failed, within a reasonable time, to give, or cause to be given, information thereof to the employer, or to some person superior to himself in the service of the employer, or who had intrusted to him some superintendence, unless it shall appear on the trial that such defect or negligence was known to such employer, or superior person, prior to such injuries to the employee; or unless such defect could have been discovered by such employer by reasonable and proper care, tests or inspection.