A power of attorney; a written instrument by which one person constitutes another his true and lawful attorney, in order that the latter may dc lor the former, and in his place and stead, some lawful act. People v. Smith, 112 Mich. 192, 70 N. W. 400, 07 Am. St. Rep. 392; Civ. Code La. 1900, art. 2985.