I'm following this tutorial:

Act as ferret tutorial

...and i'm using the personalized version of the act_as_ferret method "find_by_contents" made by the article author, named "find_storage_by_contents". The problem is that rails throw an error and it says that it cannot find (undefined method) the method "ferret_index" that is called from inside that author method.
How can it be? I have installed both ferret as a ruby gem and act_as_ferret as a rails plugin.