Under the present hygienic conditions, tetanus is not easily contracted. Even in the presence of a closed, anaerobic wound where the tetanus bacillus may grow, the body can be made to develop active immunity by timely injection of tetanus toxoid, and even if tetanus infection occurs, it will not cause severe tetanus symptoms. The root cause of tetanus is the massive growth and reproduction of tetanus bacillus in the wound, followed by the release of toxin, causing clinical symptoms. Tetanus bacillus is an anaerobic clostridial bacillus, so massive growth and multiplication of tetanus bacillus is only possible in closed, anaerobic wounds, or wounds that have not been adequately debrided.