In Ybarra v. Spangard (1944) 25 Cal.2d 486, a case involving injuries allegedly inflicted during surgery. The defendant doctors argued that the plaintiff had not shown which of the several instrumentalities that he came in contact with while in the hospital caused his injury, and thus he had not established that any one defendant had exclusive control. The Supreme Court recognized that "in a modern hospital a patient is quite likely to come under the care of a number of persons in different types of contractual and other relationships with each other. . . . But we do not believe that either the number or relationship of the defendants alone determines whether the doctrine of res ipsa loquitur applies. Every defendant in whose custody the plaintiff was placed for any period was bound to exercise ordinary care to see that no unnecessary harm came to him and each would be liable for failure in this regard." (25 Cal. 2d at pp. 491-492.) "The control, at one time or another, of one or more of the various agencies or instrumentalities which might have harmed the plaintiff was in the hands of every defendant or of his employees or temporary servants. This, we think, places upon them the burden of initial explanation. Plaintiff was rendered unconscious for the purpose of undergoing surgical treatment by the defendants; it is manifestly unreasonable for them to insist that he identify any one of them as the person who did the alleged negligent act." (Id. at p. 492.)