No party shall be compelled, in testifying or giving a deposition, to disclose the names of the witnesses by whom nor the manner in which he proposes to prove his case, nor, in giving a deposition, to produce any writing which is material to his case or defense, unless the deposition is taken in his own behalf.
RSA 516:23
1858, 2090:1. GS 209:14. GL 228:14. PS 224:14. PL 336 :25. RL 392:23.