Agent's Delegation of Powers

An agent, unless specially forbidden by his principal to do so, can delegate his powers to another person in any of the following cases, and in no others: 1. When the act to be done is purely mechanical; 2. When it is such as the agent cannot himself, and the subagent can lawfully perform; 3. When it is the usage of the place to delegate such powers; or 4. When such delegation is specially authorized by the principal.