func: function __targetExchangeAndSpendCallback(address _to, uint _amount) public whenConfigured onlyExchange returns (bool success) {
          balances[_to] = balances[_to].add(_amount);
          exchangesReceived[_to] = exchangesReceived[_to].add(_amount);
          emit ExchangeSpent(tx.origin, this, _to, _amount);
          return true;
      }