Where, in an action for negligence,the plaintiff's evidence shows that the injury caused could equallywell have been caused by other causes as by the defendant's negligence,
he has failed to discharge the burden of proof; so that a plaintiff will fail if he can only establish that the bacteria which caused him gastric disorderwere as likely to have been on the bottle containing the product complained of, or on the plaintiff~s own hands, as in the product manufactured by the defendant which the plaintiff consumed