codex vs travel book

codex

noun
  • An early manuscript book. 

  • An official list of medicines and medicinal ingredients. 

  • A book bound in the modern manner, by joining pages, as opposed to a rolled scroll. 

travel book

noun
  • A book about travelling to a certain region, such as a memoir or guide book. 

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