When an employee of an employer suffers an occupational disease and is thereby disabled from performing his work in the last occupation in which he was injuriously exposed to the hazards of such disease, or dies as a result of such disease, and the disease was due to the nature of an occupation or process in which he was employed within the period previous to his disablement as hereinafter limited, the employee, or, in case of his death, his dependents shall be entitled to compensation.