digestive system vs small intestine

digestive system

noun
  • A system of organs for the purpose of digesting food. 

small intestine

noun
  • The upper part of the intestine, between the stomach and the large intestine, divided into the duodenum, the jejunum and the ileum. 

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