began to run more strongly against restrictive patent practices. Case law Origins and development In 1917, the Supreme Court reversed the four-year-old Henry v. A.B. Dick Co. decision and established patent misuse as an affirmative defense to copyright infringement. In Motion Picture Patents Co. v. Universal Film Mfg. Co., the Supreme Court held that requiring a patented film projector only be used for screening films authorized by the patent holder was unenforceable and constituted patent misuse. The Court concluded that the patentee's attempt to extend its monopoly power beyond the rights that the patent statute conferred on it was inequitable, and because of the patentee's "unclean hands," the court, as a court of equity, would not grant it relief. In explaining its ruling, the Court said: [W]e are convinced that the exclusive right granted in every patent must be limited to the invention described in the claims of the patent, and that it is not competent for the owner of a patent, by notice attached to its machine, to in effect extend the scope of its patent monopoly by restricting the use of it to materials necessary in its operation, but which are no part of the patented invention, or to send its machines forth into the channels of trade of the country subject to conditions as to use or royalty to be paid, to be imposed thereafter at the discretion of such patent owner. The patent law furnishes no warrant for such a practice, and the cost, inconvenience, and annoyance to the public which the opposite conclusion would occasion forbid it. Carbice Corp. v. American Patents Development Corp., clarified that requiring patent licensees to buy other products as a condition of a patent license ("product tying") was misuse. American Patents Development Corp. held a patent for a dry ice transport enclosure. It required its customers only use their enclosure to transport dry ice from their exclusive distributor. The Supreme Court held that using patents to control an enclosure purchaser's other product purchases was patent misuse. (In a separate case a few months later, the Supreme Court held that Carbice's patent was invalid.) The Supreme Court held that patent misuse made the patent unenforceable regarding monetary relief in Morton Salt Co. v. G.S. Suppiger Co. Suppiger Co. owned a patent on salt-tablet dispensing machines that it manufactured. The sales agreement for the machines required customers to purchase salt tablets exclusively