No poisonous medicine decoction or substance shall be held for sale or sold, except for a lawful purpose and with proper motives and by persons competent to give the proper directions and precautions as to the use of the same; nor shall any bottle, box, parcel or receptacles thereof be delivered to any person unless the same is plainly marked on the outside "Poison," nor to any person whom the person delivering the same to has reason to think intends it for any illegal or improper use or purpose.
('68 Code, § 38.05) Penalty, see § 116.999