Trademark rights can also be lost through genericity. Sometimes, trademarks that are originally distinctive can become generic over time, thereby losing its trademark protectionKellogg Co. v. National Biscuit Co., 305 U.S. 111 (1938). A word will be considered generic when, in the minds of a substantial majority of the public, the word denotes a broad genus or type of product and not a specific source or manufacturer. So, for example, the term "thermos" has become a generic term and is no longer entitled to trademark protection. Although it once denoted a specific manufacturer, the term now stands for the general type of product. Similarly, both "aspirin" and "cellophane" have been held to be generic. Bayer Co. v. United Drug Co., 272 F.505 (S.D.N.Y. 1921). In deciding whether a term is generic, courts will often look to dictionary definitions, the use of the term in newspapers and magazines, and any evidence of attempts by the trademark owner to police its mark.