private int numPatients() {
    int count = 0 ;
    for (Mobile m : inside()) if (m instanceof Actor) {
      final Actor actor = (Actor) m ;
      if (! actor.health.conscious()) count++ ;
      else if (actor.health.injuryLevel() > 0) count++ ;
      else if (actor.isDoing(SickLeave.class, null)) count++ ;
    }
    return count ;
  }