code: def _send(self, msg):
          
          uuid = self.m2req.sender
          conn_id = self.m2req.conn_id
  
          header = "%s %d:%s," % (uuid, len(str(conn_id)), str(conn_id))
          zmq_message = header + ' ' + msg
          self.stream.send(zmq_message)
docs: Raw send to the given connection ID at the given uuid, mostly used 
          internally.