In general, what a person sui juris may do himself, he may delegate authority to another to do for him; yet there are exceptions; thus, although a person may do an unlawful act, it is clear that he can not delegate authority to another person to do it; for it is against the policy of the law to allow any such authority, and therefore the appointment is utterly void; it imports neither duty nor obligation, nor responsibility on either side; although it may involve both in punishment. Story on Ag. Sec. 11; Mechem on Ag. Sees. 18, 19, 20. Compare Sec. 987.