commercial bank vs mutual savings bank

commercial bank

noun
  • A bank whose chief business is accepting demand deposits and making short-term loans. 

mutual savings bank

noun
  • A financial institution chartered by a central or regional government, without capital stock, that is nominally owned by its members, who subscribe to a common fund. 

How often have the words commercial bank and mutual savings bank occurred in a corpus of books? (source: Google Ngram Viewer )