potentially large number of defendants. The plaintiff could not identify which particular defendant had manufactured the drug responsible for her injuries. However, her complaint alleged that the defendants were jointly and individually negligent in that they had manufactured, marketed and promoted DES as a safe drug to prevent miscarriage without adequate testing or warning of its dangerous side effects; that they had collaborated in their marketing methods, promotion and testing of the drug; that they had relied on each others' test results; that they had adhered to an industry-wide safety standard; and that they had produced the drug from a common and mutually agreed generic formula. The court distinguished Summers on the basis that in that case all the parties who were or could have been responsible for the harm to the plaintiff were joined as defendants, whereas in Sindell there were approximately 200 drug companies which had made DES, any of which might have manufactured the injury-producing drug. The court held that it would be unfair, in such circumstances, to require each defendant to exonerate itself. Further, it said that there might be a substantial likelihood that none of the five defendants joined in the action had made the DES which caused the injury, and that the offending producer, not named, would escape liability. The court surmounted this problem by adapting the Summers rule so as to apportion liability on the basis of the defendant's market share. See pp 593-595, 602-603, 604-605 and 612-613. A very similar case concerning the same drug arose in the Netherlands in B v Bayer Nederland BV (Hoge Raad, 9 October 1992, NJ 1994, 535) which turned on Article 6.99 BW. That provision is in these terms:
 Where the damage may have resulted from two or more events for each of which a different person is liable, and where it has been determined that the damage has arisen from at least one of these events, the obligation to repair the damage rests upon each of these persons, unless he proves that the damage is not the result of the event for which he himself is liable ... [Article 6.99BW] aims to remove the unfairness arising from the fact that the victim must bear his or her own damage because he or she cannot prove whose action caused his or her harm. The victims in the present case are faced with such an evidentiary difficulty . . . In para 3.7.5 of its judgment the court said:
 
It is sufficient for each DES daughter to establish . . . in relation to each of the pharmaceutical companies:

(i) that the pharmaceutical company in question put DES in circulation during the relevant period and can therefore be found liable because it committed a fault;

(ii) that another or several other producers - regardless of whether they are parties to the proceedings or not - also put DES in circulation during the relevant period and can therefore also be found liable because it (they) committed a fault; and 

(iii) that she suffered injury that resulted from the use of DES, but that it is no longer possible to determine from which producer the DES originated. In principle the burden of proof on these issues rests on the DES daughter 35