In Morris v. Pacific Electric Ry. Co. (1935) 2 Cal.2d 764, the court refused to retroactively apply an amendment of the former Vehicle Act, which eliminated a finding of negligence per se based on speeding. (2 Cal.2d at pp. 768-769.) At the time of trial, the law provided that speeding was unlawful and constituted negligence per se. (Id. at pp. 766-767.) As such, a plaintiff was unable to recover damages suffered in an accident if the plaintiff's speed contributed to the accident. (Id. at p. 767.) However, the trial court refused to instruct the jury on this existing principle of law. In absence of this instruction, the plaintiff prevailed, even though there was evidence that he was speeding immediately before the accident. (Ibid.) On appeal, the plaintiff argued that the refusal to give the negligence per se instruction, even if in error, was not prejudicial in light of an amendment to the law that occurred while the appeal was pending. (Morris, supra, 2 Cal.2d at pp. 767-768.) Thus, during the appeal, the Legislature had changed the law to provide that speeding was no longer negligence per se, and that the opposing party bore the burden of establishing that driving a vehicle at excessive speed constituted negligence. (Id. at p. 768.) The plaintiff sought to apply the amended law to his case, arguing that it was a "mere procedural change--a change in the rule of evidence--which is applicable alike to all actions, including those pending appeal at the time of its enactment ... ." (Ibid.) However, the court rejected the plaintiff's argument on the ground that "at the time of the accident involved herein the defendant had an absolute defense, based upon the finding which the jury could have made in its favor on the evidence. ... To apply the amendment now so as to cut off such a substantial defense would be arbitrary and unjust." (Morris, supra, 2 Cal.2d at pp. 768-769.) In so holding, the court relied on the principle that "the legislature may not, under pretense of regulating procedure or rules of evidence, deprive a party of a substantive right, such as a good cause of action or an absolute or a substantial defense ... ." (Id. at p. 768.)