If any Company registered under this Act carries on business when the number of its shareholders is less than seven, for a period of six months after the number has been so reduced, then every Director of such Company during the time that it so carries on business after such period of six months, shall be severally liable for the payment of the whole debts of the Company contracted during such time, and may be sued for the same without the joinder in the action or suit of any other person.