there was some separation in time of the negligent acts. For example, we cited the analysis in Butzow v. Wausau Memorial Hosp. 51 Wis. 2d 281, 288-289, 187 N.W.2d 349 (1971)(original tortfeasor and physician jointly and severally liable only for aggravation of damages), and Restatement (Second) of Torts § 879 (1979)(discussing situations where the tortfeasors can be jointly liable only for the aggravation of initial injuries; in other situations, the tortfeasors can be jointly liable for the entire harm). The Farrell court also cited Sumnicht v. Toyota Motor Sales, U.S.A., 121 Wis. 2d 338, 359, 360 N.W.2d 2 (1984) (if more than one tortfeasor contributed to the injury, the law of joint and several liability applies); and Arbet v. Gussarson, 66 Wis. 2d 551, 557, 225 N.W.2d 431 (1975) (<HOLDING>). See Farrell, 151 Wis. 2d at 60 n.3. In
holding that district court did not abuse its discretion in refusing to permit a design defect products liability expert to submit an untimely addendum stating a new claim of failure to warn after defense expert refuted the basis of original design defect opinion holding that it was not important that the automobiles design defect did not actually cause the initial accident as long as it was a substantial factor in causing burn injury after gas tank erupted holding that notice of a defect could not be imputed to a defendant inasmuch as it created the defect holding that it is not holding that complaint alleging design defect likely to cause damage failed to state a claim