lymphatic system vs lymphoid system

lymphatic system

noun
  • In mammals, including humans, a network of lymph vessels and lymph nodes that transport fluid, fats, proteins, and lymphocytes to the bloodstream as lymph, and remove microorganisms and other debris from tissues. 

lymphoid system

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