The Commissioner shall perform or cause to be performed a post-mortem examination in any case where the cause of death cannot otherwise be definitely determined or in cases where there are reasons to believe that death may have been due to a disease the knowledge of which gained by such post-mortem examination would be of importance in guarding the health of the community. No post-mortem examination shall be performed contrary to the wish of the personal representative of the deceased unless there are reasonable grounds to believe that such deceased died as a result of an illegal act or acts or from a quarantinable disease, or from suicide.