An important artifact in the history of mental pollution is found between pages 90 and 91 of the 1974 paperback edition of Robert Silverberg’s sci-fi novel Time Hoppers. Here, permanently interjected by the publisher into the flow of the story, the unsuspecting reader will stumble upon a double-sided, full colour advertisement hawking Kent brand cigarettes, “with a famous micronite filter.” This relic represents an early bumbling attempt at the commercialization of knowledge through the direct placement of advertising within books. Three decades later, the tricks of the marketers have grown far more sophisticated, and readers are now accustomed to being assaulted by an ad on every digital page.

Google was not the first to dream the sinister fantasy of interrupting thinking itself with advertising, but the corporation's near monopoly on the organization of knowledge ensures that they are the first with the power to pull it off. No longer primarily a search engine, 99 per cent of Google's income comes from advertising, and this has profoundly skewed their corporate priorities. Google's concern now is with how to transform every online text into mere fodder for commercial interjections. Look beyond the advertisements that line the top and right of the search results page. Ignore for a moment that Google’s acquisition of DoubleClick in 2008 for $31 billion has made the corporation the biggest player in the placement of advertisements on other people’s websites. Focus instead on the greatest coup of them all: Google's audacious plan to digitize the storehouse of human wisdom by scanning every book ever published -  advertising itself on every page, branding its logo onto the mind of every future reader.

The race to commercialize knowledge is well underway. Amazon’s new e-book reader has exchanged advertisements for screensavers, portending a future where ads are placed dynamically within e-book, for example. Reversing the tide is only possible within a mental environmentalist framework that recognizes mental carcinogens as no less dangerous than physical pollutants.