doxology vs introit

doxology

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

introit

noun
  • An anthem or psalm sung before a Communion service 

  • A prayer, typically part of a psalm or other portion of the Bible, read or sung at the start of Mass while or immediately after the priest ascends to the altar. 

  • A composition of vocal music sung at the opening of a church service. 

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