In Putensen v. Clay Adams, Inc. (1970) 12 Cal.App.3d 1062, the court upheld a nonsuit in favor of defendant, a manufacturer of surgical tubing, where there was evidence that it had been tampered with and weakened by someone at the hospital. The court said: "Adverting to the second condition exclusive control we observe that in dealing with the question whether it is more probable than not that the defendant's negligence caused the accident, it must be shown that the defendant had the management or control of the agency or instrumentality which caused the accident in order to eliminate the possibility that the accident was caused by someone other than the defendant. " (At p. 1075.)