§ 3121. Physical or mental examination. (a) Notice of examination. After commencement of an action in which the mental or physical condition or the blood relationship of a party, or of an agent, employee or person in the custody or under the legal control of a party, is in controversy, any party may serve notice on another party to submit to a physical, mental or blood examination by a designated physician, or to produce for such examination his agent, employee or the person in his custody or under his legal control. The notice may require duly executed and acknowledged written authorizations permitting all parties to obtain, and make copies of, the records of specified hospitals relating to such mental or physical condition or blood relationship; where a party obtains a copy of a hospital record as a result of the authorization of another party, he shall deliver a duplicate of the copy to such party. A copy of the notice shall be served on the person to be examined. It shall specify the time, which shall be not less than twenty days after service of the notice, and the conditions and scope of the examination. (b) Copy of report. A copy of a detailed written report of the examining physician setting out his findings and conclusions shall be delivered by the party seeking the examination to any party requesting to exchange therefor a copy of each report in his control of an examination made with respect to the mental or physical condition in controversy.