How have courts interpreted the law of insanity in the context of a jury trial?

"The latter portion of [the challenged] instruction, beginning with the conjunction 'or,' does not strictly follow the beaten paths established by this [36 Cal.App.4th 1272] court in declaring what constitutes insanity, and beaten paths are always safer than new and untried ones; and while, owing to the peculiar wording of the instruction, it is not probable that it in any degree enlightened the jury as to the law of the case, yet upon a fair construction, we think it comes within the law of insanity as legally applicable to the present case, and vaguely states in a different form the same principle found in the former portion of the instruction. If a man commits a homicide under an insane impulse, and at the time does not possess sufficient reason to understand the nature of the act, he certainly is in such a condition of mind that he is incapable of weighing the moral qualities of the act, and determining therefrom whether it is right or wrong; and we think this to be its legitimate construction. The instruction surely bears no relationship to the theory of irresistible impulse, frowned upon and rejected in People v. Hoin [ (1882) 62 Cal. 120], and does not, either in letter or spirit, countenance the doctrine, which is there cast out, as having no place in the law of insanity in this state. In addition to this instruction, the court fully and correctly stated to the jury the law of insanity in numerous other portions of its charge, and we are satisfied that no material injury resulted to defendant from the charge we have just considered." (Marceau v. Travellers' Ins. Co., supra, 101 Cal. at p. 346, 36 P. 813.)