An authority expressed in general terms, however broad, does not authorize an agent to act in his own name, unless it is the usual course of business to do so. Source: CivC 1877, § 1361, subdiv 1; CL 1887, § 3984, subdiv 1; RCivC 1903, § 1680, subdiv 1; RC 1919, § 1262 (1); SDC 1939, § 3.0205 (1).