An agent also owes duties to his principal and to third parties. He must use the utmost care in protecting his principal's interests. He must not make any secret profits himself and any contracts he may make must be accounted for to his principal. He must strictly obey the lawful instructions that his principal may give him, and is liable to the principal for any loss to the latter that the agent's negligence and lack of care may cause. He must use reasonable prudence in carrying out the affairs of his principal that have been intrusted to him. Generally speaking, an agent must act in person and cannot delegate his authority to some one else. That is, if A authorizes B to act as his agent, B cannot turn over this agency to C, for A has a right to say whom he wishes to act as his agent. An agent must also, whenever demanded, give complete reports to his principal. An agent is liable to third parties if he exceeds his authority in such a way that his principal is not bound, and thus is liable for any fraud committed by him while on the principal's business. Suppose A makes a contract with B, telling B that he is acting for X. As a matter of fact X does not exist. Then A is liable to B. If an agent makes a contract with third parties in such a way that his principal is not bound, then the agent is liable himself. "We, as Directors of the A. B. Corporation, promise to pay to X's order five hundred dollars. C, D, E, Directors of the A. B. Corporation;" in this case the A. B. Corporation is liable, for it is the corporation's promise. Suppose the note had read "We promise to pay, etc.," and had been signed by C, D and E; here the corporation would not be liable, but C, D and E would be liable individually. Suppose an agent does not disclose the name of his principal. When the third party finds out who the principal is, then he may hold either the agent or the principal (but not both).