dirty books vs filth

dirty books

filth

noun
  • Smut; that which sullies or defiles the moral character; corruption; pollution. 

  • The police. 

  • Dirt; foul matter; that which soils or defiles. 

  • A vile or disgusting person. 

How often have the words dirty books and filth occurred in a corpus of books? (source: Google Ngram Viewer )