It is a general rule of law that since the agent himself is a delegate, he cannot redelegate the authority delegated to him. The maxim is "Delegatus non potest delegare," but the rule is not without exceptions, though resting on good ground. Where the authority granted carries with it duties of a personal nature and trust, the rule cannot be departed from,9 but where the act is a ministerial one, not involving the exercise of judgment, or discretion, or skill, the agent may delegate another to perform the act,10 or in any case when this act apparently was contemplated by the principal. Sometimes the circumstances of the case imply authority to redelegate certain duties, where it is unreasonable to suppose the agent would personally perform them. The express contract governs, if it speaks the parties' intentions plainly. A general custom or usage, will also be read into the contract as a part of it so as to permit a sub-agent to act, in the absence of a term to the contrary.11