asylum vs mental hospital

asylum

noun
  • A place of safety or refuge. 

  • The protection, physical and legal, afforded by such a place (as, for example, for political refugees). 

mental hospital

noun
  • A hospital facility designed to treat persons with serious mental disorders, as opposed to disorders of the body. 

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