 The second sort of test here is one that adopts general rules of legal causation. Such rules are adopted for various policy reasons also having nothing to do with causation, but such rules differ from the ad hoc test by their eschewal of case-by-case balancing; rather, it is the per se rules of legal causation that are adopted for policy reasons. Thus, at common-law the rule for homicide was that death must occur within a year and a day of the defendant’s harmful action, else he could not be said to have legally caused the death. Analogously, the last wrongdoer rule of both torts and criminal law held that when a single victim is mortally wounded by two or more assailants, acting seriatim over time and not in concert, only the last wrongdoer could be said to be the legal cause of the death. As a third example, tort law for a time observed what was called a “first house rule”, according to which a railroad whose negligently emitted sparks burned an entire town was only liable for the house or houses directly ignited by its sparks, not for other houses ignited by the burning of those first burnt houses (Ryan v. New York Central RR). There is no pretense of making truly causal discriminations by such rules; rather, such rules were adopted for explicit reasons of legal policy. The first house rule, for example, was said to be justified by the policy of subsidizing the then developing railroad industry by protecting it from a liability that was thought to be potentially ruinous in its extent.