All notes, certificates of indebtedness, and other obligations of townships of the second class issued for money borrowed or for work done or materials furnished, where the money was actually loaned or the work done or materials furnished, be and hereby they are ratified, confirmed, and validated, notwithstanding that, at the time of the issue thereof, no tax was levied for the payment of the principal and interest, and that no statement was filed in the court of quarter sessions prior to the issue thereof: Provided, however, That in any suit or action on such notes, certificates, or obligations, the township may defend as to the amount of money loaned or as to the value of the work done or materials furnished, whether such certificates be held by the original holder or an assignee or transferee.