doxology vs introitus

doxology

noun
  • An expression of praise to God, especially a short hymn sung as part of a Christian worship service. 

introitus

noun
  • A piece of music played before a mass; a musical introduction of any sort. 

  • The entrance to a hollow organ or canal; often specifically the entrance to the vagina. 

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