Mitigation of damages.

The owner of such dog shall, however, be entitled to plead and prove in mitigation of damages that he had no knowledge of any circumstances indicating such dog to be or to have been vicious or dangerous or mischievous, and, if he does so, he shall be liable only to the extent of the actual expenses incurred by the person so bitten or injured as a result of the bite or injury.

(Acts 1953, No. 320, p. 379, §2.)