mammy vs progenitrix

mammy

noun
  • mamma; mother 

  • In the southern United States, a black nanny employed to look after white children; or in the antebellum South, a female slave who was close to the household and looked after the children. 

progenitrix

noun
  • A female progenitor, a foremother, any of a person's direct female ancestors (ancestresses). 

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